THE EFFICACY OF INCORPORATING PARTIAL SQUATS IN MAXIMAL STRENGTH TRAINING CALEB D. BAZYLER,1 KIMITAKE SATO,1 CRAIG A. WASSINGER,2 HUGH S. LAMONT,3 MICHAEL H. STONE1
AND
Departments of 1Exercise and Sport Science, East Tennessee University, Johnson City, Tennessee; 2Physical Therapy, East Tennessee State University, Johnson City, Tennessee; and 3Department of Exercise Science, California Lutheran University, Thousand Oaks, California ABSTRACT Bazyler, CD, Sato, K, Wassinger, CA, Lamont, HS, and Stone, MH. The efficacy of incorporating partial squats in maximal strength training. J Strength Cond Res 28(11): 3024–3032, 2014—The purpose of our study was to examine the effects of 2 different training methods on dynamic and isometric measures of maximal strength. Seventeen recreationally trained men (1 repetition maximum [1RM] squat: 146.9 6 22.4 kg) were assigned to 2 groups: full range of motion (ROM) squat (F) and full ROM with partial ROM squat (FP) for the 7-week training intervention. Repeated measures analysis of variance revealed that there was a statistically significant group-by-time interaction for impulse scaled at 50, 90, and 250 milliseconds at 908 of knee flexion and rate of force development at 200 milliseconds with 1208 of knee flexion (p # 0.05). There was also a statistically significant time effect (p # 0.05) for the 1RM squat, 1RM partial squat, isometric squat peak force allometrically scaled (IPFa) 908, IPFa 1208, and impulse allometrically scaled at 50, 90, 200, and 250 milliseconds at 908 and 1208 of knee flexion. Additionally, the FP group achieved statistically larger relative training intensities (%1RM) during the final 3 weeks of training (p # 0.05). There was a trend for FP to improve over F in 1RM squat (+3.1%, d = 0.53 vs. 0.32), 1RM partial squat (+4.7%, d = 0.95 vs. 0.69), IPFa 1208 (+5.7%, d = 0.52 vs. 0.12), and impulse scaled at 50, 90, 200, and 250 milliseconds at 908 (+6.3 to 13.2%, d = 0.50–1.01 vs. 0.30– 0.57) and 1208 (+3.4 to 16.8%, d = 0.45–1.11 vs. 0.08–0.37). These larger effect sizes in the FP group can likely be explained by their ability to train at larger relative training intensities during the final 3 weeks of training resulting in superior training adaptations. Our findings suggest that partial ROM squats in conjunction with full ROM squats may be an effective training method for improving maximal strength and early force-time curve characteristics in men
Address correspondence to Caleb D. Bazyler, [email protected]. edu. 28(11)/3024–3032 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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with previous strength training experience. Practically, partial squats may be beneficial for strength and power athletes during a strength-speed mesocycle while peaking for competition.
KEY WORDS partial lifts, isometric, impulse, peak force, full range of motion
INTRODUCTION
P
artial lifts are often incorporated into strength and conditioning training programs (8,9,16,32). Proposed benefits include improved strength at the terminal range of motion (ROM) and weak portions of a movement (9,25,37), substitute for full ROM exercise during rehabilitation (2,30), injury prevention (2), enhanced metabolic adaptations (34), increased training volume (8), training variation (27), and enhanced sport performance (9,37). Only a few studies directly examine their efficacy in improving maximal strength and the findings are conflicting (6,11,12,17,24,25,30,35). Previous research has documented the specificity of ROM in strength training that shows adaptations incurred are specific to the ROM trained (6,7,9,11,17). In one of the earliest studies, Graves et al. (11) found that isometric strength gains for the full ROM bilateral knee extension group were similar throughout the entire ROM at all knee angles tested, whereas strength gains for partial ROM groups were greater in the trained than in the untrained joint angles tested. Clark et al. (9) reported similar findings, where the group training at varying ROM on the bench press improved over the full ROM group in isokinetic bench press in the terminal portion of the movement, ½ ROM bench press throw peak force, and full ROM bench press throw displacement. Bloomquest et al. (6) found statistical improvements in front thigh muscle cross-sectional area (CSA) at the most proximal sites for the partial ROM squat group, whereas the full ROM squat group improved at all sites. These results strongly support specificity of ROM in training adaptations. Studies directly examining the efficacy of partial ROM squat training on maximal strength and jump performance (1 repetition maximum [1RM] squat, counter movement jump [CMJ] height, squat jump height) have elucidated
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Journal of Strength and Conditioning Research similar findings. Hartmann et al. (17) found training full ROM back squat attained statistically larger elevations in CMJ height and 1RM squat over the quarter squat group, whereas the quarter squat group improved 1RM quarter squat over full the ROM group. These results were similar to Bloomquest et al. (6) who found training full ROM squat statistically improved 1RM squat more than the partial ROM group, whereas the partial ROM group statistically improved 1RM partial squat more than the full ROM group. A limitation of previous studies is that bar displacement was not included in work estimates (6,17,30,35). Equalizing work using relative % 1RM or volume load (VL) does not take into consideration the large differences in bar displacement between a full and partial ROM lift. Not taking displacement into consideration for work approximations poses a threat to internal validity considering the study questions are related to ROM specific training adaptations and their effect on performance at corresponding joint angles (9). Examining the findings from the aforementioned studies, there is evidence that partial squats augment full ROM 1RM strength in untrained subjects. However, in individuals with previous strength training experience removing full ROM squats may result in a plateau and possible decrease in full ROM 1RM strength (16,28). In previous studies, the groups training partial ROM did not perform full ROM training (6,17,30,35). To fulfill specificity requirements the partial ROM group should continue with full ROM training if the training goal is to improve 1RM in a full ROM. Additionally, some studies used untrained subjects while evidence indicates that partial lifts, if effective, would benefit lifters with previous training experience (9,25,27). Indeed, observations by the authors indicate that many strength-power athletes, including weightlifters and powerlifters, integrate partial movements into their training. Wilson et al. (36) proposed that partial lifts involving supramaximal loads may result in reduced inhibition lending to an increase in maximal force production. The increase in maximal force production with training may also result in increases in rate of force development (RFD) (1,14); however, these are likely through different processes (20). Training with partial lifts may improve peak force, RFD and impulse in that ROM to a greater extent than full ROM training alone (37). The terminal range of motion is loaded more optimally with a partial ROM lift than a full ROM lift because the full ROM lift is limited by the sticking point. Considering that many sports involve countermovements from knee and hip angles similar to those in a partial squat, has lead previous researchers to suggest that partial squats may improve athletic performance by increasing strength and explosiveness in the corresponding joint angles (9,37). However, the effects of training with partial squats on isometric squat kinetic variables at these important joint angles have yet to be examined. The purpose of this study was to examine the effects of 2 different training modalities, full ROM training (F) and full
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ROM plus partial ROM training (FP), using recreationally trained males during a 7-week training intervention. We hypothesized that both groups would improve from pre- to postintervention on all dynamic and isometric variables measured; FP would improve to a greater extent than F at measurements associated with maximum effort at the terminal ROM (1RM partial squat, 1208 isometric squat peak force, RFD, and impulse scaled).
METHODS Experimental Approach to the Problem
Subjects were ranked according to absolute and relative 1RM squat from preintervention testing and randomly assigned to a group. One group performed F, whereas the other performed FP during the 7-week intervention. Training was conducted 2 days per week with a minimum of 48 hours rest between training sessions. Dynamic and isometric strength were measured pre- and postintervention through 1RM and isometric squat, respectively. Table 1 describes the 12-week training program and testing sessions. Subjects
Subjects recruited were 18 recreationally trained college aged males with at least 1 year of resistance training experience on the squat ($1.3 body mass). Preintervention 1RM squat was similar to previous studies: 146.9 6 22.4 kg (16,19,38). Nine subjects in the F group (age: 20.8 6 2.0 years, height: 176.4 6 6.3 cm, body mass: 84.9 6 10.9 kg, 1RM squat/body mass: 1.75 6 0.11) and 8 subjects in the FP group (age: 20.9 6 1.9 years, height: 179.0 6 6.8 cm, body mass: 84.6 6 8.4 kg, 1RM squat/body mass: 1.71 6 0.27) completed the study. One subject from the FP group was an outlier for dynamic testing variables (.2 SD from the mean) and was excluded from the study. Throughout the study, subjects were instructed to cease any supplementation use, refrain from lower-body resistance training outside of the study, and they were instructed not to participate in physical activity 24 hours before testing or training sessions. Subjects also completed a dietary log 24 hours before both preintervention testing sessions and were instructed to replicate the log for postintervention testing. Before participating, all subjects completed a health history questionnaire and signed an informed consent form in accordance with the guidelines set forth by the university’s Institutional Review Board. Training
After eligibility was determined by 1RM squat testing (T0), subjects trained 2 days per week for 3 weeks in a strengthendurance phase to equilibrate the training program for all subjects. During this phase, subjects were familiarized with partial squats and isometric squats to minimize learning effects on testing results and to record bar heights and knee angles for subsequent testing and training. During the intervention, work accomplished (VLd) was estimated using the following equation (13,22): VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Efficacy of Partial ROM Squat
TABLE 1. Strength training program.* Phase
Week
Strength-endurance and familiarization Pretesting Strength phase 1 Deload Strength phase 2 Posttesting
Day 1 438 438 438 Dynamic 3 3 5 or 3 3 5 or 3 3 5 or 3 3 3 or 3 3 3 or 3 3 3 or 3 3 3 or Dynamic
1 2 3 4 5 6 7 8 9 10 11 12
%1RM 75–80 77.5–82.5 80–85
6 6 6 6 7 7 7
3 3 3 3 3 3 3
5† 5 5 3 3z 3 3
85–87 86–88 87–89 75 88–90 89–91 90–92
Day 2 338 338 338 Isometric 3 3 5 or 3 3 5 or 3 3 5 or 3 3 3 or 3 3 3 or 3 3 3 or 3 3 3 or Isometric
% Reduction 10–15 10–15 10–15
6 6 6 6 7 7 6
3 3 3 3 3 3 3
5 5 5 3 3 3 3
10–15 10–15 15–20 15–20 10–15 10–15 15–20
*RM = repetition maximum. †F (full ROM) performed 6 3 5 on squats; FP (full plus partial ROM) performed 3 3 5 on squats and partial squats. zF performed 6–7 3 3 on squats; FP performed 3 3 3 on squats and partial squats.
Estimated Work ðVLdÞ kg$m ¼ Mass of external load kg 3Displacement ðmÞ3Repetitions:
Squat bar displacement was measured manually using a measuring tape. Warm-up sets and working sets were included in the VLd calculation. Test-retest reliability was intraclass correlation coefficients (ICC) = 0.97. Subjects were required to complete .80% of the programmed VLd to be included in the data analysis. Relative training intensity (TI) for each session was calculated by dividing the average load used by the subject’s 1RM for the corresponding lift (%1RM). Groups followed a block-periodized model to control for volume and intensity manipulation (28,33). Subjects trained with heavy and light days to manage fatigue and avoid training to failure. Squat load differed by 10–15% between heavy and light days with light days performed on the second day of the microcycle. Load for squat and partial squat was calculated using percentage of preintervention 1RM. Each training session began with a dynamic warm-up followed by warm-up sets on squat. The F group performed full squats only, whereas the FP group performed full squats followed by partial squats (from 1008 knee angle to lockout position). All training sessions were supervised to ensure correct technique and safety. Testing Procedures
Anthropometrics, 1RM squat, and 1RM partial squat were measured at the beginning of weeks 4 and 12 dynamic testing sessions. Isometric squat peak force, RFD from 0 to 50, 0 to 90, 0 to 200, and 0 to 250 milliseconds and impulse
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scaled from 0 to 50, 0 to 90, 0 to 200, and 0 to 250 milliseconds were assessed during the isometric testing session, which occurred 72–96 hours after dynamic testing. Subjects reported to the laboratory on day 1 of weeks 4 and 12 at predesignated times. Body composition was measured with Lange calipers (Cambridge Scientific Industries, Cambridge, MD) using the sum of 7 skinfolds (3). Dynamic Strength Assessment. Dynamic warm-up followed anthropometric measurements. The 1RM squat was tested first followed by 1RM partial squat at 1008 knee angle (measured in the sagittal plane using the greater trochanter, the lateral condyle of the femur, the head of the fibula, and the lateral malleolus as bony landmarks). The 1RM protocols involved a progressive increase in load and decrease in reps per set (26). Attempts were selected with the goal of reaching their maximum in 3 attempts after warm-up. Four minutes of rest was given between each attempt. Back squat depth was determined as the top of the leg at the hip joint being below the knee (38). Subjects rested at least 5 minutes between 1RM squat and partial squat testing. For partial squats, the bar was set on safety pins at a height corresponding to 1008 of knee flexion, as determined during the familiarization sessions. Subjects performed the concentric portion of the squat to a full lockout position then lowered the bar back down to the safety pins. The same assistant recorded knee angle and bar height for all testing and training sessions.
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Journal of Strength and Conditioning Research Isometric Strength Assessment. Kinetic variables were measured on 0.45 3 0.91 m dual force platforms affixed side by side (Rice Lake Weighing Systems, Rice Lake, WI, USA) sampling at 1,000 Hz. Isometric squat testing at 908 and 1208 was performed to provide an indication of changes in force-time characteristics at 2 important segments of the squat; approximately 908 is considered the sticking point of the squat and approximately 1208 is where peak isometric torque of the knee extensors is produced (5,31). Subjects performed a dynamic warm-up followed by 2 warm-up attempts at 50 and 75% maximal effort at 908. After the 2-minute rest period, 2 maximal efforts were performed with 3 minutes rest in between. The bar was placed across the back in the same position used in training. The same assistant recorded knee angle and bar height for all testing sessions. The tester instructed subjects to push as fast and as hard as possible (20). The tester shouted “push” and participants pushed maximally into the ground until peak force was reached when the tester shouted “stop” to end the test. After completing testing at 908, subjects were given 5 minutes rest, and the same protocol with warm-up attempts was repeated at 1208. Subjects were tested at the same time of the day for both test days (15). The force-time curve data were smoothed using an 11-point moving average (all data points equally weighted) and analyzed with Labview software (ver. 2010, National Instruments, Austin, TX, USA). The average of 2 attempts on the isometric squat at 90 and 1208 were used for analysis.
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Figure 1. Changes in 1RM squat and 1RM partial squat. *p # 0.05, statistical change from pretest. F = full ROM; FP = full plus partial ROM; RM = repetition maximum; ROM = range of motion.
partial ROM training, this study was exploratory and Bonferonni adjustment was not used to decrease the possibility of committing a type II error (23). SPSS software (version 20) was used to perform all statistical analyses (IMB Co., New York, NY, USA).
RESULTS Dynamic Strength Assessment
Statistical Analyses
A Shapiro-Wilks normality test was used to determine whether the data were normally distributed. Levene’s test was used to determine homogeneity of variance. Intraclass correlation coefficients were calculated to determine testretest reliability. Coefficient of variation (CV) was calculated to assess relative measurement error. Preintervention values of both groups were tested for significant differences using a 1-way analysis of variance (ANOVA). A 2 3 2 repeated measures ANOVA was used to assess main effects and interactions for all dependent variables. If a statistical time effect was found, a paired sample t-test was used to determine changes within groups. Effect sizes were calculated as Cohen’s d. A default 90% confidence interval was chosen to make probabilistic magnitude-based inferences about the values of the outcome variables (4). An effect was unclear if chances of the true value being substantially positive and negative were both .5%. The probabilities that the true difference in performance were positive, trivial, or negative are expressed as percentages derived using a published spreadsheet (21). The qualitative terms for corresponding percentages are most unlikely, ,0.5%; very unlikely, 0.5– 5%; unlikely, 5–25%; possibly, 25–75%; likely, 75–95%; very likely, 95–99.5%; and most likely, .99.5%. Pearson’s product-moment correlation was used to assess relationships between dependent variables. For all tests, the alpha level was set at p # 0.05. Because of the paucity of research on
One Repetition Maximum Squat. No group-by-time interaction was found for 1RM squat. A statistical time effect (p , 0.001) was found for 1RM squat. One repetition maximum squat in F increased by 5.1 6 4.5%, d = 0.32, and in FP by 8.2 6 2.1%, d = 0.53 (Figure 1). For both groups, the change in 1RM squat was most likely positive (F: 99.5%
Figure 2. Changes in IPFa at 90 and 1208 of knee flexion. 1808 is full extension. *p # 0.05, statistical change from pretest. F = full ROM; FP = full plus partial ROM; IPFa = isometric squat peak force allometrically scaled; ROM = range of motion.
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Efficacy of Partial ROM Squat
Figure 3. A) Changes in impulse scaled at 908. *p # 0.05, statistical change from pretest. #p # 0.05, statistical group-by-time interaction. B) Changes in impulse scaled at 1208. *p # 0.05, statistical change from pretest. F = full ROM; FP = full plus partial ROM; ROM = range of motion.
positive, 0.4% trivial, 0.1% negative; FP: 100% positive, 0% trivial, 0% negative). One Repetition Maximum Partial Squat. No group-by-time interaction was found for 1RM partial squat. A statistically significant time effect (p , 0.001) was found for 1RM partial squat. One repetition maximum partial squat in F increased by 10.2 6 11.7%, d = 0.69, and in FP by 14.9 6 11.8%, d = 0.95. The change in 1RM partial squat was very likely positive in the F group (F: 97.3% positive, 0.8% trivial, 1.9% negative) and most likely positive in the FP group (FP: 99.7% positive, 0.1% trivial, 0.2% negative). Isometric Strength Assessment
Isometric Squat Peak Force Scaled. No group-by-time interaction was found for isometric squat peak force allometrically
scaled (IPFa) at 90 or 1208 of knee flexion. A statistically significant time effect was found for IPFa 908 and IPFa 1208 (p # 0.05). Paired t-test results indicated that IPFa at 908 increased by 5.3 6 4.5%, d = 0.81 in the F group (p = 0.008) and IPFa at 1208 increased by 8.9 6 8.6%, d = 0.52 in the FP group (p = 0.02) (Figure 2). Changes occurring at 908 for the FP group and 1208 for the F group were not statistically significant. The change in IPFa 908 was very likely positive in the F group (F: 99.4% positive, 0.4% trivial, 0.2% negative) and unclear in the FP group (FP: 68.6% positive, 14.2% trivial, 17.1% negative). The change in IPFa 1208 was unclear in the F group (F: 78.9% positive, 9.4% trivial, 11.7% negative) and very likely positive in the FP group (FP: 98.4% positive, 0.6% trivial, 1.0% negative). Test-retest reliability using ICC for IPFa 908 and 1208 was 0.97 and 0.98, respectively. It is important to note that homogeneity of
Figure 4. A) Microcycle VLd. Depicts estimated work completed by subjects during training intervention microcycles. No statistical difference between groups for VLd at any microcyle. B) Microcycle relative training intensity. Depicts relative training intensity (TI) completed by subjects during training intervention microcyles. Relative TI was statistically greater (*p # 0.05) in the FP group at weeks 9, 10, and 11. FP = full plus partial ROM, ROM = range of motion, F = full ROM; VL = volume load.
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Figure 5. A) Changes in force-time curve with training. Figure displays changes in early force-time curve characteristics for FP, pre- to postintervention. B) Changes in force-time curve with training. Figure displays changes in early force-time curve characteristics for F, pre- to postintervention. F = full ROM, FP = full plus partial ROM, ROM = range of motion.
variance for IPFa 908 was not met (p = 0.02) indicating that although good reliability of the test-retest exists, a large magnitude of variances between groups were present for IPFa 908. Isometric Squat Impulse Scaled. A group-by-time interaction was found for impulse scaled at 908 of knee flexion for 50, 90, and 250 milliseconds, whereas no group-by-time interaction was found for any time point at 1208 of knee flexion. A statistically significant time effect was found at all time points for both knee angles (p # 0.05). Paired t-tests showed a statistical increase from pretraining in FP for all time points with 90 and 1208 (p # 0.05), but for F only at 250 milliseconds with 1208 (p = 0.049) (Figures 3A, B). Effect size for impulse scaled at 50, 90, 200, and 250 milliseconds for 908 was d = 0.30, 0.33, 0.53, and 0.57 in the F group, respectively, and d = 1.01, 0.65, 0.50, and 0.66 in the FP group, respectively. Effect size for impulse scaled at 50, 90, 200, and 250 milliseconds for 1208 was d = 0.08, 0.22, 0.37, and 0.34 in the F group, respectively, and d = 1.11, 0.83, 0.52, and 0.45 in the FP group, respectively. Test-retest reliability was determined to be ICC .0.92 for all time points measured. It is important to note that homogeneity of variance for impulse scaled at 200 and 250 milliseconds with 908 was not met (p = 0.04 and 0.02, respectively) indicating that although reliability of the testretest exists, a large magnitude of variances between groups were present for impulse scaled at 200 and 250 milliseconds at 908 of knee flexion. Isometric Squat Rate of Force Development. There were no statistical changes found for RFD at any time points measured in either group. A statistically significant groupby-time interaction (p = 0.037) was found for RFD at 200 milliseconds with 1208 of knee flexion. However, paired t-test results showed that changes within groups were not statistically significant after postintervention testing (p . 0.05). Effect sizes were ,0.3, and CVs ranged from 19.6 to 48.7% for RFD
results. Test-retest reliability for all time points at 908 showed an ICC ranging from 0.74 to 0.9 and 200 and 250 milliseconds at 1208 ranging from 0.76 to 0.94. Rate of force development at 50 and 90 milliseconds with 1208 were excluded because of low test-retest reliability (ICC ,0.7). Body Composition. There was no statistical difference between groups during pre- and posttesting for any of the anthropometric variables. A time effect was found for body fat percentage (p # 0.05). Body fat percentage decreased statistically by 10.3 6 12.4%, d = 0.27 (p = 0.027) in the F group; however, the decrease did not reach statistical significance in the FP group, 5.3 6 11.1%, d = 0.12 (p = 0.102). Estimated Work and Relative Training Intensity. A 1-way ANOVA showed no difference between groups for total VLd. The mean values for total VLd in F were 30,907 6 5985 kg$m and in FP were 30,584 6 5601 kg$m. VLd accomplished during each microcycle in the training intervention is depicted in Figure 4A. Despite the similarities in VLd accomplished, 1-way ANOVA results showed the FP group trained at a statistically greater overall relative TI during the intervention. The mean values for relative TI in F were 77.63 6 3.43% 1RM and in FP were 81.84 6 4.35% 1RM. Further analysis revealed that FP trained at a statistically larger relative TI at weeks 9, 10, and 11 of the training intervention (Figure 4B). Correlations. A strong statistical correlation was found between 1RM squat and IPFa 908 (r = 0.72, p , 0.001), whereas a moderate statistical correlation was found between 1RM squat and IPFa 1208 (r = 0.45, p = 0.005). A strong statistical correlation was found between the change in 1RM squat pre- to postintervention and overall relative TI (r = 0.64, p = 0.003). A moderate statistical correlation was found between the change in IPFa 908 pre- to postintervention and full ROM squat VLd (r = 0.42, p = 0.048) (Figure 5A). VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Efficacy of Partial ROM Squat DISCUSSION The purpose of this study was to examine the effects of 2 different training exercises, full ROM training, and full ROM plus partial ROM training, on recreationally trained men during 7 weeks of training. Primary findings for dynamic strength were a statistical improvement in 1RM squat and partial squat in both groups with a 3.1 and 4.7% greater improvement in the FP group, respectively. For isometric strength, the F group statistically improved IPFa 908 by 5.3% and the FP group statistically improved IPFa 1208 by 8.9%. Additionally, the larger relative training intensities accomplished by the FP group during the final 3 weeks of training suggests superior adaptations. These findings support previous claims that partial plus full ROM training is an effective strategy for improving maximal strength in subjects with previous strength training experience (9,27,37). Combined mean 1RM increased by 7.0% from T0 to preintervention, 6.7% from pre- to postintervention testing, and a total increase of 14.2% over the 12 weeks. These findings are similar to training studies that have found increases in 1RM squat ranging from 10 to 20% over a 9to 15-week period (16,19,29). Both groups improved 1RM squat at slightly different rates (F by 5.1%, FP by 8.2%); however, there was no statistical difference between groups. These findings are in agreement with Massey et al. (25) who found no difference in 1RM bench press between full ROM and mixed training (full ROM bench press plus partial ROM bench press) 2 days per week for 10 weeks. Similar to the findings for 1RM squat, both groups statistically improved 1RM partial squat from pretraining values with a 4.7% larger rate of gain in the FP group (10.2 vs. 14.9%); however, there was no statistical difference between groups. These findings are comparable to Bloomquest et al. (6) who reported a 20 and 36% increase for partial 1RM squat in the full ROM and partial ROM group, respectively, with the increase in the partial ROM group being statistically greater than the full ROM group after 12 weeks of training 2 days per week. The reason for the smaller increase in our findings is likely because of the difference in training status. Their subjects were untrained men, thus, a larger comparative increase in strength measures is expected and is consistent with previous research (18,33). Another possible explanation is the differences in knee angles used during training. Their subjects in the partial squat group trained at 1208 compared with 1008 in our study; thus, the heavier loads and shorter bar paths may have resulted in larger changes in 1RM partial squat. This study along with corroborative findings suggests that specificity of ROM in training plays a significant role in the adaptation process (6,9,11,16,17). Although there were no statistical differences between groups for VLd, the FP group was able to train at a higher relative TI during the final 3 weeks of the intervention. The strong statistical correlation between change in 1RM squat
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and relative TI along with the slightly larger effect sizes for 1RM squat and partial squat in the FP group suggests superior training adaptations. These findings support previous claims that partial ROM squat with supramaximal loads enhance full ROM maximal strength in lifters with previous training experience (36,37). Alternatively, the lower relative TI in the F group may be explained by the greater number of sets performed through the full ROM, which limited the load they were capable of lifting. Previous research on partial ROM training has not investigated force-time characteristics during isometric contractions of the movement trained with the exception of Clark et al. (9) who measured isometric peak force at quarter ROM bench press. Similar to findings by Blazevich et al. (5), a strong statistical correlation was found between IPFa 908 and 1RM squat, however, the correlation between IPFa 1208 and 1RM squat was statistically significant, but not as strong. This suggests that force produced through the sticking point is more closely related to 1RM squat strength than force produced in the terminal ROM. However, only the F group statistically improved IPFa 908 although FP had a 3.1% greater improvement in 1RM squat. The larger percent increases in 1RM squat and partial squat in the FP group may be alternatively explained by greater improvements in impulse scaled at 3 of the 4 time points measured at 908. Although there were no statistical differences between groups for 1RM squat and IPFa 908, the F group improved IPFa 908 over FP by a 3.8% margin and the FP group improved 1RM squat over F by a 3.1% margin. Considering the strong relationship between 1RM squat and IPFa 908, these results seem conflicting. One possible explanation is that the F group had a greater potential for improvement on IPFa 908 (preintervention mean: 107.51 6 6.96 vs. 114.85 6 13.60, in the F and FP, respectively). Although there was no statistical difference between groups for total VLd, the greater volume of full ROM squats performed by the F group may also explain the difference between groups as evidenced by the moderate correlation between full ROM squat VLd and the change in IPFa 908. Practically speaking, these data suggest that improvements in strength at the sticking point seem to be directly related to the VLd performed through the corresponding joint angles. In contrast to IPFa 908 results, FP improved IPFa 1208 by 5.7% over F, although there was no statistical interaction. Consistent with previous studies, the greater loads used during partial ROM training resulted in the ability to produce higher forces at a knee angle similar to the ROM trained (9,36,37). For applications to strength athletes, this would be advantageous for geared powerlifters who need to produce higher forces at the terminal ROM where they have less support from their gear (10). Full ROM plus partial ROM training statistically improved impulse scaled at all time points measured for both knee angles, whereas F only improved impulse scaled at 250 milliseconds with 1208 (p = 0.049). These findings seem to
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Journal of Strength and Conditioning Research agree with Clark et al. (9) who found greater improvements in isokinetic bench press peak force at 458$s21 in the terminal portion of the movement, ½ bench press throw peak force, and full bench press throw displacement in the group that trained with variable ROM over full ROM alone. As depicted in Figure 5A, the FP group achieved a larger left and upward shift in the earlier time points of the force-time curve, which has significant implications for strength-power athletes. The greater improvements in impulse scaled at earlier time points with 908 knee flexion may explain why FP improved 1RM squat although there was no statistical improvement in IPFa 908. Increased impulse scaled could be beneficial for 1RM strength because it may enhance ability to get through the sticking point. The larger left and upward shift in the force-time curve in the FP group explains the larger percent increase in impulse scaled at earlier time points (Figure 5A) and suggests RFD increased over those time periods, although no statistical difference was found for RFD in either group from pre- to postintervention. Considering the small effect sizes (,0.3) and large CVs (19.6–48.7%) for RFD at all time points, impulse scaled seems to be a better representation of changes during the early stages of isometric squat force production. In summary, partial lifts are often incorporated into resistance training programs aimed at improving maximal strength. The primary finding of our study was a trend for FP to improve over F in 1RM squat (+3.1%, d = 0.53 vs. 0.32), 1RM partial squat (+4.7%, d = 0.95 vs. 0.69), IPFa 1208 (+5.7%, d = 0.52 vs. 0.12), and impulse scaled at 50, 90, 200, and 250 milliseconds at 908 (+6.3 to 13.2%, d = 0.50–1.01 vs. 0.30–0.57) and 1208 (+3.4 to 16.8%, d = 0.45–1.11 vs. 0.08– 0.37). The FP group also trained at an overall greater relative TI, which was strongly correlated with change in 1RM squat, indicating superior adaptations. The larger effect sizes for measures of strength and explosiveness in the FP group can likely be explained the larger relative TI in the final 3 weeks of training. These findings demonstrate that partial plus full ROM training can be an effective training modality for improving maximal strength. However, further research is needed to ascertain whether combined training is more effective than full ROM training alone. Future studies on partial ROM training should include analysis of kinetic and kinematic variables during athletic movements (such as CMJ, 40-m sprint, and agility testing), longer training programs, measures of CSA with total work controlled, and different training exercises (bench press and deadlift).
PRACTICAL APPLICATIONS Partial ROM training has been proposed as an effective training modality for improving strength and power in the terminal ROM (9,36,37). These authors claim that partial ROM training more optimally loads the terminal ROM where joint angles, the force-velocity relationship, and movement patterns are more similar to those in sport.
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Although the subjects in this study were not athletes, their strength level was comparable to previous research on athletes (9,16,19). Findings of this study suggest that combined training may be more effective than full ROM training alone for improving early force-time curve characteristics. The larger effect sizes for IPFa 1208 (0.48) and impulse scaled with 1208 (0.45–1.11) in the FP group have implications for strength-power athletes. For example, the contact time for an elite sprinter is approximately 90 milliseconds, the effect size for impulse scaled at 90 milliseconds at 1208 knee angle was 0.83 vs. 0.22 in FP and F, respectively. For an elite sprinter, producing larger forces in that narrow time window may be the difference between winning vs. losing. This study also supports the use of partial ROM training as an effective means of providing variation in a training program for experienced lifters. As discussed previously, at higher training levels, variation becomes a larger component of the program design. Thus, from a practical standpoint, partial ROM training could be incorporated during a strength-speed mesocycle in preparation for a strengthpower athlete’s upcoming competition.
ACKNOWLEDGMENTS The authors confirm that there is no conflict of interest associated with this publication, and that there has been no financial support for this study that could have influenced its outcome. The authors thank the ETSU sports science students for assisting with the strength training and data collection.
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12. Graves, JE, Pollock, ML, Leggett, SH, Carpenter, DM, Fix, CK, and Fulton, MN. Limited range-of-motion lumbar extension strength training. Med Sci Sports Exerc 24: 128–133, 1992. 13. Haff, GG. Quantifying workloads in resistance training: a brief review. Strength and Cond 10: 31–40, 2010. 14. Ha¨kkinen, K, Komi, PV, and Alen, M. Effect of explosive type strength training on isometric force- and relaxation-time, electromyographic and muscle fibre characteristics of leg extensor muscles. Acta Physiol Scand 125: 587–600, 1985. 15. Ha¨kkinen, K, Pakarinen, A, Alen, M, Kauhanen, H, and Komi, PV. Neuromuscular and hormonal responses in elite athletes to two successive strength training sessions in one day. Eur J Appl Physiol Occup Physiol 57: 133–139, 1988. 16. Harris, G, Stone, M, O’Bryant, H, Proulx, C, and Johnson, R. Short-term performance effects of high power, high force, or combined weight-training methods. J Strength Cond Res 14: 14–21, 2000. 17. Hartmann, H, Wirth, K, Klusemann, M, Dalic, J, Matuschek, C, and Schmidtbleicher, D. Influence of squatting depth on jumping performance. J Strength Cond Res 26: 3243–3261, 2012. 18. Hoffman, J. Physiological Aspects of Sport Training and Performance. Champaign, IL: Human Kinetics, 2002. 19. Hoffman, JR, Ratamess, NA, Lkatt, M, Faigenbaum, AD, Ross, RE, Tranchina, NM, McCurley, RC, Kang, J, and Kraemer, WJ. Comparison between different offseason resistance training programs in Division III American college football players. J Strength Cond Res 23: 11–19, 2009. 20. Holtermann, A, Roeleveld, K, Vereijken, B, and Ettema, G. The effect of rate of force development on maximal force production: acute and training-related aspects. Eur J Appl Physiol 99: 605–613, 2007. 21. Hopkins, W. A spreadsheet for deriving a confidence interval, mechanistic inference and clinical inference from a p value. Sportscience 11: 16–20, 2007. 22. Hornsby, W, Gentles, J, Miller, J, and Stone, M. Volume load and training intensity with and without exercise displacement. In: Proceedings of 41st Annual Congress of the American College of Sports Medicine Southeast Regional Chapter. Greenville, SC: South Carolina, 2013. pp. 39. 23. Huberty, CJ and Morris, JD. Multivariate analysis versus multiple univariate analyses. Psychol Bull 105: 302–308, 1989.
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26. McGuigan, MR, Winchester, JB, and Erickson, T. The importance of isometric maximum strength in college wrestlers. J Sports Sci Med 5: 108–113, 2006. 27. Mookerjee, S and Ratamess, N. Comparison of strength differences and joint action durations between full and partial range-of-motion bench press exercise. J Strength Cond Res 13: 76–81, 1999. 28. Painter, KB, Haff, GG, Ramsey, MW, McBride, J, Triplett, T, Sands, WA, Lamont, HS, Stone, ME, and Stone, MH. Strength gains: block versus daily undulating periodization weight training among track and field athletes. Int J Sports Physiol Perform 7: 161– 169, 2012. 29. Peterson, MD, Dodd, DJ, Alvar, AB, Rhea, MR, and Fave, M. Undulation training for the development of hierarchal fitness and improved firefighter job performance. J Strength Cond Res 22: 1683– 1695, 2008. 30. Pinto, RS, Gomes, N, Radaelli, R, Botton, CE, Brown, LE, and Bottaro, M. Effect of range of motion on muscle strength and thickness. J Strength Cond Res 26: 2140–2145, 2012. 31. Smidt, GL. Biomechanical analysis of knee flexion and extension. J Biomech 6: 79–92, 1973. 32. Stone, MH, Potteiger, JA, and Pierce, KC. Comparison of the effects of three different weight-training programs on the one repetition maximum squat. J Strength Cond Res 14: 332–337, 2000. 33. Stone, M, Stone, M, and Sands, W. Principles and Practice of Resistance Training. Champaign, IL: Human Kinetics, 2007. 34. Sullivan, JJ, Knowlton, RG, Devita, P, and Brown, DD. Cardiovascular response to restricted range of motion resistance exercise. J Strength Cond Res 10: 3–7, 1996. 35. Weiss, LW, Fry, AC, Wood, L, Relyea, GE, and Melton, C. Comparative effects of deep versus shallow squat and leg-press training on vertical jumping ability and related factors. J Strength Cond Res 14: 241–247, 2000. 36. Wilson, G, Murphy, A, and Walshe, A. The specificity of strength training: the effect of posture. Eur J Appl Physiol Occup Physiol 73: 346–352, 1996. 37. Zatsiorsky, V. Science and Practice of Strength Training. Champaign, IL: Human Kinetics, 1995. 38. Zourdos, MC and Kim, JS. Physiological responses to two different models of daily undulating periodization in trained powerlifters. Dissertation, Florida State University, Tallahassee, 2012.
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Departments of 1Exercise and Sport Science, East Tennessee University, Johnson City, Tennessee; 2Physical Therapy, East Tennessee State University, Johnson City, Tennessee; and 3Department of Exercise Science, California Lutheran University, Thousand Oaks, California ABSTRACT Bazyler, CD, Sato, K, Wassinger, CA, Lamont, HS, and Stone, MH. The efficacy of incorporating partial squats in maximal strength training. J Strength Cond Res 28(11): 3024–3032, 2014—The purpose of our study was to examine the effects of 2 different training methods on dynamic and isometric measures of maximal strength. Seventeen recreationally trained men (1 repetition maximum [1RM] squat: 146.9 6 22.4 kg) were assigned to 2 groups: full range of motion (ROM) squat (F) and full ROM with partial ROM squat (FP) for the 7-week training intervention. Repeated measures analysis of variance revealed that there was a statistically significant group-by-time interaction for impulse scaled at 50, 90, and 250 milliseconds at 908 of knee flexion and rate of force development at 200 milliseconds with 1208 of knee flexion (p # 0.05). There was also a statistically significant time effect (p # 0.05) for the 1RM squat, 1RM partial squat, isometric squat peak force allometrically scaled (IPFa) 908, IPFa 1208, and impulse allometrically scaled at 50, 90, 200, and 250 milliseconds at 908 and 1208 of knee flexion. Additionally, the FP group achieved statistically larger relative training intensities (%1RM) during the final 3 weeks of training (p # 0.05). There was a trend for FP to improve over F in 1RM squat (+3.1%, d = 0.53 vs. 0.32), 1RM partial squat (+4.7%, d = 0.95 vs. 0.69), IPFa 1208 (+5.7%, d = 0.52 vs. 0.12), and impulse scaled at 50, 90, 200, and 250 milliseconds at 908 (+6.3 to 13.2%, d = 0.50–1.01 vs. 0.30– 0.57) and 1208 (+3.4 to 16.8%, d = 0.45–1.11 vs. 0.08–0.37). These larger effect sizes in the FP group can likely be explained by their ability to train at larger relative training intensities during the final 3 weeks of training resulting in superior training adaptations. Our findings suggest that partial ROM squats in conjunction with full ROM squats may be an effective training method for improving maximal strength and early force-time curve characteristics in men
Address correspondence to Caleb D. Bazyler, [email protected]. edu. 28(11)/3024–3032 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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with previous strength training experience. Practically, partial squats may be beneficial for strength and power athletes during a strength-speed mesocycle while peaking for competition.
KEY WORDS partial lifts, isometric, impulse, peak force, full range of motion
INTRODUCTION
P
artial lifts are often incorporated into strength and conditioning training programs (8,9,16,32). Proposed benefits include improved strength at the terminal range of motion (ROM) and weak portions of a movement (9,25,37), substitute for full ROM exercise during rehabilitation (2,30), injury prevention (2), enhanced metabolic adaptations (34), increased training volume (8), training variation (27), and enhanced sport performance (9,37). Only a few studies directly examine their efficacy in improving maximal strength and the findings are conflicting (6,11,12,17,24,25,30,35). Previous research has documented the specificity of ROM in strength training that shows adaptations incurred are specific to the ROM trained (6,7,9,11,17). In one of the earliest studies, Graves et al. (11) found that isometric strength gains for the full ROM bilateral knee extension group were similar throughout the entire ROM at all knee angles tested, whereas strength gains for partial ROM groups were greater in the trained than in the untrained joint angles tested. Clark et al. (9) reported similar findings, where the group training at varying ROM on the bench press improved over the full ROM group in isokinetic bench press in the terminal portion of the movement, ½ ROM bench press throw peak force, and full ROM bench press throw displacement. Bloomquest et al. (6) found statistical improvements in front thigh muscle cross-sectional area (CSA) at the most proximal sites for the partial ROM squat group, whereas the full ROM squat group improved at all sites. These results strongly support specificity of ROM in training adaptations. Studies directly examining the efficacy of partial ROM squat training on maximal strength and jump performance (1 repetition maximum [1RM] squat, counter movement jump [CMJ] height, squat jump height) have elucidated
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Journal of Strength and Conditioning Research similar findings. Hartmann et al. (17) found training full ROM back squat attained statistically larger elevations in CMJ height and 1RM squat over the quarter squat group, whereas the quarter squat group improved 1RM quarter squat over full the ROM group. These results were similar to Bloomquest et al. (6) who found training full ROM squat statistically improved 1RM squat more than the partial ROM group, whereas the partial ROM group statistically improved 1RM partial squat more than the full ROM group. A limitation of previous studies is that bar displacement was not included in work estimates (6,17,30,35). Equalizing work using relative % 1RM or volume load (VL) does not take into consideration the large differences in bar displacement between a full and partial ROM lift. Not taking displacement into consideration for work approximations poses a threat to internal validity considering the study questions are related to ROM specific training adaptations and their effect on performance at corresponding joint angles (9). Examining the findings from the aforementioned studies, there is evidence that partial squats augment full ROM 1RM strength in untrained subjects. However, in individuals with previous strength training experience removing full ROM squats may result in a plateau and possible decrease in full ROM 1RM strength (16,28). In previous studies, the groups training partial ROM did not perform full ROM training (6,17,30,35). To fulfill specificity requirements the partial ROM group should continue with full ROM training if the training goal is to improve 1RM in a full ROM. Additionally, some studies used untrained subjects while evidence indicates that partial lifts, if effective, would benefit lifters with previous training experience (9,25,27). Indeed, observations by the authors indicate that many strength-power athletes, including weightlifters and powerlifters, integrate partial movements into their training. Wilson et al. (36) proposed that partial lifts involving supramaximal loads may result in reduced inhibition lending to an increase in maximal force production. The increase in maximal force production with training may also result in increases in rate of force development (RFD) (1,14); however, these are likely through different processes (20). Training with partial lifts may improve peak force, RFD and impulse in that ROM to a greater extent than full ROM training alone (37). The terminal range of motion is loaded more optimally with a partial ROM lift than a full ROM lift because the full ROM lift is limited by the sticking point. Considering that many sports involve countermovements from knee and hip angles similar to those in a partial squat, has lead previous researchers to suggest that partial squats may improve athletic performance by increasing strength and explosiveness in the corresponding joint angles (9,37). However, the effects of training with partial squats on isometric squat kinetic variables at these important joint angles have yet to be examined. The purpose of this study was to examine the effects of 2 different training modalities, full ROM training (F) and full
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ROM plus partial ROM training (FP), using recreationally trained males during a 7-week training intervention. We hypothesized that both groups would improve from pre- to postintervention on all dynamic and isometric variables measured; FP would improve to a greater extent than F at measurements associated with maximum effort at the terminal ROM (1RM partial squat, 1208 isometric squat peak force, RFD, and impulse scaled).
METHODS Experimental Approach to the Problem
Subjects were ranked according to absolute and relative 1RM squat from preintervention testing and randomly assigned to a group. One group performed F, whereas the other performed FP during the 7-week intervention. Training was conducted 2 days per week with a minimum of 48 hours rest between training sessions. Dynamic and isometric strength were measured pre- and postintervention through 1RM and isometric squat, respectively. Table 1 describes the 12-week training program and testing sessions. Subjects
Subjects recruited were 18 recreationally trained college aged males with at least 1 year of resistance training experience on the squat ($1.3 body mass). Preintervention 1RM squat was similar to previous studies: 146.9 6 22.4 kg (16,19,38). Nine subjects in the F group (age: 20.8 6 2.0 years, height: 176.4 6 6.3 cm, body mass: 84.9 6 10.9 kg, 1RM squat/body mass: 1.75 6 0.11) and 8 subjects in the FP group (age: 20.9 6 1.9 years, height: 179.0 6 6.8 cm, body mass: 84.6 6 8.4 kg, 1RM squat/body mass: 1.71 6 0.27) completed the study. One subject from the FP group was an outlier for dynamic testing variables (.2 SD from the mean) and was excluded from the study. Throughout the study, subjects were instructed to cease any supplementation use, refrain from lower-body resistance training outside of the study, and they were instructed not to participate in physical activity 24 hours before testing or training sessions. Subjects also completed a dietary log 24 hours before both preintervention testing sessions and were instructed to replicate the log for postintervention testing. Before participating, all subjects completed a health history questionnaire and signed an informed consent form in accordance with the guidelines set forth by the university’s Institutional Review Board. Training
After eligibility was determined by 1RM squat testing (T0), subjects trained 2 days per week for 3 weeks in a strengthendurance phase to equilibrate the training program for all subjects. During this phase, subjects were familiarized with partial squats and isometric squats to minimize learning effects on testing results and to record bar heights and knee angles for subsequent testing and training. During the intervention, work accomplished (VLd) was estimated using the following equation (13,22): VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Efficacy of Partial ROM Squat
TABLE 1. Strength training program.* Phase
Week
Strength-endurance and familiarization Pretesting Strength phase 1 Deload Strength phase 2 Posttesting
Day 1 438 438 438 Dynamic 3 3 5 or 3 3 5 or 3 3 5 or 3 3 3 or 3 3 3 or 3 3 3 or 3 3 3 or Dynamic
1 2 3 4 5 6 7 8 9 10 11 12
%1RM 75–80 77.5–82.5 80–85
6 6 6 6 7 7 7
3 3 3 3 3 3 3
5† 5 5 3 3z 3 3
85–87 86–88 87–89 75 88–90 89–91 90–92
Day 2 338 338 338 Isometric 3 3 5 or 3 3 5 or 3 3 5 or 3 3 3 or 3 3 3 or 3 3 3 or 3 3 3 or Isometric
% Reduction 10–15 10–15 10–15
6 6 6 6 7 7 6
3 3 3 3 3 3 3
5 5 5 3 3 3 3
10–15 10–15 15–20 15–20 10–15 10–15 15–20
*RM = repetition maximum. †F (full ROM) performed 6 3 5 on squats; FP (full plus partial ROM) performed 3 3 5 on squats and partial squats. zF performed 6–7 3 3 on squats; FP performed 3 3 3 on squats and partial squats.
Estimated Work ðVLdÞ kg$m ¼ Mass of external load kg 3Displacement ðmÞ3Repetitions:
Squat bar displacement was measured manually using a measuring tape. Warm-up sets and working sets were included in the VLd calculation. Test-retest reliability was intraclass correlation coefficients (ICC) = 0.97. Subjects were required to complete .80% of the programmed VLd to be included in the data analysis. Relative training intensity (TI) for each session was calculated by dividing the average load used by the subject’s 1RM for the corresponding lift (%1RM). Groups followed a block-periodized model to control for volume and intensity manipulation (28,33). Subjects trained with heavy and light days to manage fatigue and avoid training to failure. Squat load differed by 10–15% between heavy and light days with light days performed on the second day of the microcycle. Load for squat and partial squat was calculated using percentage of preintervention 1RM. Each training session began with a dynamic warm-up followed by warm-up sets on squat. The F group performed full squats only, whereas the FP group performed full squats followed by partial squats (from 1008 knee angle to lockout position). All training sessions were supervised to ensure correct technique and safety. Testing Procedures
Anthropometrics, 1RM squat, and 1RM partial squat were measured at the beginning of weeks 4 and 12 dynamic testing sessions. Isometric squat peak force, RFD from 0 to 50, 0 to 90, 0 to 200, and 0 to 250 milliseconds and impulse
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scaled from 0 to 50, 0 to 90, 0 to 200, and 0 to 250 milliseconds were assessed during the isometric testing session, which occurred 72–96 hours after dynamic testing. Subjects reported to the laboratory on day 1 of weeks 4 and 12 at predesignated times. Body composition was measured with Lange calipers (Cambridge Scientific Industries, Cambridge, MD) using the sum of 7 skinfolds (3). Dynamic Strength Assessment. Dynamic warm-up followed anthropometric measurements. The 1RM squat was tested first followed by 1RM partial squat at 1008 knee angle (measured in the sagittal plane using the greater trochanter, the lateral condyle of the femur, the head of the fibula, and the lateral malleolus as bony landmarks). The 1RM protocols involved a progressive increase in load and decrease in reps per set (26). Attempts were selected with the goal of reaching their maximum in 3 attempts after warm-up. Four minutes of rest was given between each attempt. Back squat depth was determined as the top of the leg at the hip joint being below the knee (38). Subjects rested at least 5 minutes between 1RM squat and partial squat testing. For partial squats, the bar was set on safety pins at a height corresponding to 1008 of knee flexion, as determined during the familiarization sessions. Subjects performed the concentric portion of the squat to a full lockout position then lowered the bar back down to the safety pins. The same assistant recorded knee angle and bar height for all testing and training sessions.
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Journal of Strength and Conditioning Research Isometric Strength Assessment. Kinetic variables were measured on 0.45 3 0.91 m dual force platforms affixed side by side (Rice Lake Weighing Systems, Rice Lake, WI, USA) sampling at 1,000 Hz. Isometric squat testing at 908 and 1208 was performed to provide an indication of changes in force-time characteristics at 2 important segments of the squat; approximately 908 is considered the sticking point of the squat and approximately 1208 is where peak isometric torque of the knee extensors is produced (5,31). Subjects performed a dynamic warm-up followed by 2 warm-up attempts at 50 and 75% maximal effort at 908. After the 2-minute rest period, 2 maximal efforts were performed with 3 minutes rest in between. The bar was placed across the back in the same position used in training. The same assistant recorded knee angle and bar height for all testing sessions. The tester instructed subjects to push as fast and as hard as possible (20). The tester shouted “push” and participants pushed maximally into the ground until peak force was reached when the tester shouted “stop” to end the test. After completing testing at 908, subjects were given 5 minutes rest, and the same protocol with warm-up attempts was repeated at 1208. Subjects were tested at the same time of the day for both test days (15). The force-time curve data were smoothed using an 11-point moving average (all data points equally weighted) and analyzed with Labview software (ver. 2010, National Instruments, Austin, TX, USA). The average of 2 attempts on the isometric squat at 90 and 1208 were used for analysis.
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Figure 1. Changes in 1RM squat and 1RM partial squat. *p # 0.05, statistical change from pretest. F = full ROM; FP = full plus partial ROM; RM = repetition maximum; ROM = range of motion.
partial ROM training, this study was exploratory and Bonferonni adjustment was not used to decrease the possibility of committing a type II error (23). SPSS software (version 20) was used to perform all statistical analyses (IMB Co., New York, NY, USA).
RESULTS Dynamic Strength Assessment
Statistical Analyses
A Shapiro-Wilks normality test was used to determine whether the data were normally distributed. Levene’s test was used to determine homogeneity of variance. Intraclass correlation coefficients were calculated to determine testretest reliability. Coefficient of variation (CV) was calculated to assess relative measurement error. Preintervention values of both groups were tested for significant differences using a 1-way analysis of variance (ANOVA). A 2 3 2 repeated measures ANOVA was used to assess main effects and interactions for all dependent variables. If a statistical time effect was found, a paired sample t-test was used to determine changes within groups. Effect sizes were calculated as Cohen’s d. A default 90% confidence interval was chosen to make probabilistic magnitude-based inferences about the values of the outcome variables (4). An effect was unclear if chances of the true value being substantially positive and negative were both .5%. The probabilities that the true difference in performance were positive, trivial, or negative are expressed as percentages derived using a published spreadsheet (21). The qualitative terms for corresponding percentages are most unlikely, ,0.5%; very unlikely, 0.5– 5%; unlikely, 5–25%; possibly, 25–75%; likely, 75–95%; very likely, 95–99.5%; and most likely, .99.5%. Pearson’s product-moment correlation was used to assess relationships between dependent variables. For all tests, the alpha level was set at p # 0.05. Because of the paucity of research on
One Repetition Maximum Squat. No group-by-time interaction was found for 1RM squat. A statistical time effect (p , 0.001) was found for 1RM squat. One repetition maximum squat in F increased by 5.1 6 4.5%, d = 0.32, and in FP by 8.2 6 2.1%, d = 0.53 (Figure 1). For both groups, the change in 1RM squat was most likely positive (F: 99.5%
Figure 2. Changes in IPFa at 90 and 1208 of knee flexion. 1808 is full extension. *p # 0.05, statistical change from pretest. F = full ROM; FP = full plus partial ROM; IPFa = isometric squat peak force allometrically scaled; ROM = range of motion.
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Efficacy of Partial ROM Squat
Figure 3. A) Changes in impulse scaled at 908. *p # 0.05, statistical change from pretest. #p # 0.05, statistical group-by-time interaction. B) Changes in impulse scaled at 1208. *p # 0.05, statistical change from pretest. F = full ROM; FP = full plus partial ROM; ROM = range of motion.
positive, 0.4% trivial, 0.1% negative; FP: 100% positive, 0% trivial, 0% negative). One Repetition Maximum Partial Squat. No group-by-time interaction was found for 1RM partial squat. A statistically significant time effect (p , 0.001) was found for 1RM partial squat. One repetition maximum partial squat in F increased by 10.2 6 11.7%, d = 0.69, and in FP by 14.9 6 11.8%, d = 0.95. The change in 1RM partial squat was very likely positive in the F group (F: 97.3% positive, 0.8% trivial, 1.9% negative) and most likely positive in the FP group (FP: 99.7% positive, 0.1% trivial, 0.2% negative). Isometric Strength Assessment
Isometric Squat Peak Force Scaled. No group-by-time interaction was found for isometric squat peak force allometrically
scaled (IPFa) at 90 or 1208 of knee flexion. A statistically significant time effect was found for IPFa 908 and IPFa 1208 (p # 0.05). Paired t-test results indicated that IPFa at 908 increased by 5.3 6 4.5%, d = 0.81 in the F group (p = 0.008) and IPFa at 1208 increased by 8.9 6 8.6%, d = 0.52 in the FP group (p = 0.02) (Figure 2). Changes occurring at 908 for the FP group and 1208 for the F group were not statistically significant. The change in IPFa 908 was very likely positive in the F group (F: 99.4% positive, 0.4% trivial, 0.2% negative) and unclear in the FP group (FP: 68.6% positive, 14.2% trivial, 17.1% negative). The change in IPFa 1208 was unclear in the F group (F: 78.9% positive, 9.4% trivial, 11.7% negative) and very likely positive in the FP group (FP: 98.4% positive, 0.6% trivial, 1.0% negative). Test-retest reliability using ICC for IPFa 908 and 1208 was 0.97 and 0.98, respectively. It is important to note that homogeneity of
Figure 4. A) Microcycle VLd. Depicts estimated work completed by subjects during training intervention microcycles. No statistical difference between groups for VLd at any microcyle. B) Microcycle relative training intensity. Depicts relative training intensity (TI) completed by subjects during training intervention microcyles. Relative TI was statistically greater (*p # 0.05) in the FP group at weeks 9, 10, and 11. FP = full plus partial ROM, ROM = range of motion, F = full ROM; VL = volume load.
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Figure 5. A) Changes in force-time curve with training. Figure displays changes in early force-time curve characteristics for FP, pre- to postintervention. B) Changes in force-time curve with training. Figure displays changes in early force-time curve characteristics for F, pre- to postintervention. F = full ROM, FP = full plus partial ROM, ROM = range of motion.
variance for IPFa 908 was not met (p = 0.02) indicating that although good reliability of the test-retest exists, a large magnitude of variances between groups were present for IPFa 908. Isometric Squat Impulse Scaled. A group-by-time interaction was found for impulse scaled at 908 of knee flexion for 50, 90, and 250 milliseconds, whereas no group-by-time interaction was found for any time point at 1208 of knee flexion. A statistically significant time effect was found at all time points for both knee angles (p # 0.05). Paired t-tests showed a statistical increase from pretraining in FP for all time points with 90 and 1208 (p # 0.05), but for F only at 250 milliseconds with 1208 (p = 0.049) (Figures 3A, B). Effect size for impulse scaled at 50, 90, 200, and 250 milliseconds for 908 was d = 0.30, 0.33, 0.53, and 0.57 in the F group, respectively, and d = 1.01, 0.65, 0.50, and 0.66 in the FP group, respectively. Effect size for impulse scaled at 50, 90, 200, and 250 milliseconds for 1208 was d = 0.08, 0.22, 0.37, and 0.34 in the F group, respectively, and d = 1.11, 0.83, 0.52, and 0.45 in the FP group, respectively. Test-retest reliability was determined to be ICC .0.92 for all time points measured. It is important to note that homogeneity of variance for impulse scaled at 200 and 250 milliseconds with 908 was not met (p = 0.04 and 0.02, respectively) indicating that although reliability of the testretest exists, a large magnitude of variances between groups were present for impulse scaled at 200 and 250 milliseconds at 908 of knee flexion. Isometric Squat Rate of Force Development. There were no statistical changes found for RFD at any time points measured in either group. A statistically significant groupby-time interaction (p = 0.037) was found for RFD at 200 milliseconds with 1208 of knee flexion. However, paired t-test results showed that changes within groups were not statistically significant after postintervention testing (p . 0.05). Effect sizes were ,0.3, and CVs ranged from 19.6 to 48.7% for RFD
results. Test-retest reliability for all time points at 908 showed an ICC ranging from 0.74 to 0.9 and 200 and 250 milliseconds at 1208 ranging from 0.76 to 0.94. Rate of force development at 50 and 90 milliseconds with 1208 were excluded because of low test-retest reliability (ICC ,0.7). Body Composition. There was no statistical difference between groups during pre- and posttesting for any of the anthropometric variables. A time effect was found for body fat percentage (p # 0.05). Body fat percentage decreased statistically by 10.3 6 12.4%, d = 0.27 (p = 0.027) in the F group; however, the decrease did not reach statistical significance in the FP group, 5.3 6 11.1%, d = 0.12 (p = 0.102). Estimated Work and Relative Training Intensity. A 1-way ANOVA showed no difference between groups for total VLd. The mean values for total VLd in F were 30,907 6 5985 kg$m and in FP were 30,584 6 5601 kg$m. VLd accomplished during each microcycle in the training intervention is depicted in Figure 4A. Despite the similarities in VLd accomplished, 1-way ANOVA results showed the FP group trained at a statistically greater overall relative TI during the intervention. The mean values for relative TI in F were 77.63 6 3.43% 1RM and in FP were 81.84 6 4.35% 1RM. Further analysis revealed that FP trained at a statistically larger relative TI at weeks 9, 10, and 11 of the training intervention (Figure 4B). Correlations. A strong statistical correlation was found between 1RM squat and IPFa 908 (r = 0.72, p , 0.001), whereas a moderate statistical correlation was found between 1RM squat and IPFa 1208 (r = 0.45, p = 0.005). A strong statistical correlation was found between the change in 1RM squat pre- to postintervention and overall relative TI (r = 0.64, p = 0.003). A moderate statistical correlation was found between the change in IPFa 908 pre- to postintervention and full ROM squat VLd (r = 0.42, p = 0.048) (Figure 5A). VOLUME 28 | NUMBER 11 | NOVEMBER 2014 |
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Efficacy of Partial ROM Squat DISCUSSION The purpose of this study was to examine the effects of 2 different training exercises, full ROM training, and full ROM plus partial ROM training, on recreationally trained men during 7 weeks of training. Primary findings for dynamic strength were a statistical improvement in 1RM squat and partial squat in both groups with a 3.1 and 4.7% greater improvement in the FP group, respectively. For isometric strength, the F group statistically improved IPFa 908 by 5.3% and the FP group statistically improved IPFa 1208 by 8.9%. Additionally, the larger relative training intensities accomplished by the FP group during the final 3 weeks of training suggests superior adaptations. These findings support previous claims that partial plus full ROM training is an effective strategy for improving maximal strength in subjects with previous strength training experience (9,27,37). Combined mean 1RM increased by 7.0% from T0 to preintervention, 6.7% from pre- to postintervention testing, and a total increase of 14.2% over the 12 weeks. These findings are similar to training studies that have found increases in 1RM squat ranging from 10 to 20% over a 9to 15-week period (16,19,29). Both groups improved 1RM squat at slightly different rates (F by 5.1%, FP by 8.2%); however, there was no statistical difference between groups. These findings are in agreement with Massey et al. (25) who found no difference in 1RM bench press between full ROM and mixed training (full ROM bench press plus partial ROM bench press) 2 days per week for 10 weeks. Similar to the findings for 1RM squat, both groups statistically improved 1RM partial squat from pretraining values with a 4.7% larger rate of gain in the FP group (10.2 vs. 14.9%); however, there was no statistical difference between groups. These findings are comparable to Bloomquest et al. (6) who reported a 20 and 36% increase for partial 1RM squat in the full ROM and partial ROM group, respectively, with the increase in the partial ROM group being statistically greater than the full ROM group after 12 weeks of training 2 days per week. The reason for the smaller increase in our findings is likely because of the difference in training status. Their subjects were untrained men, thus, a larger comparative increase in strength measures is expected and is consistent with previous research (18,33). Another possible explanation is the differences in knee angles used during training. Their subjects in the partial squat group trained at 1208 compared with 1008 in our study; thus, the heavier loads and shorter bar paths may have resulted in larger changes in 1RM partial squat. This study along with corroborative findings suggests that specificity of ROM in training plays a significant role in the adaptation process (6,9,11,16,17). Although there were no statistical differences between groups for VLd, the FP group was able to train at a higher relative TI during the final 3 weeks of the intervention. The strong statistical correlation between change in 1RM squat
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and relative TI along with the slightly larger effect sizes for 1RM squat and partial squat in the FP group suggests superior training adaptations. These findings support previous claims that partial ROM squat with supramaximal loads enhance full ROM maximal strength in lifters with previous training experience (36,37). Alternatively, the lower relative TI in the F group may be explained by the greater number of sets performed through the full ROM, which limited the load they were capable of lifting. Previous research on partial ROM training has not investigated force-time characteristics during isometric contractions of the movement trained with the exception of Clark et al. (9) who measured isometric peak force at quarter ROM bench press. Similar to findings by Blazevich et al. (5), a strong statistical correlation was found between IPFa 908 and 1RM squat, however, the correlation between IPFa 1208 and 1RM squat was statistically significant, but not as strong. This suggests that force produced through the sticking point is more closely related to 1RM squat strength than force produced in the terminal ROM. However, only the F group statistically improved IPFa 908 although FP had a 3.1% greater improvement in 1RM squat. The larger percent increases in 1RM squat and partial squat in the FP group may be alternatively explained by greater improvements in impulse scaled at 3 of the 4 time points measured at 908. Although there were no statistical differences between groups for 1RM squat and IPFa 908, the F group improved IPFa 908 over FP by a 3.8% margin and the FP group improved 1RM squat over F by a 3.1% margin. Considering the strong relationship between 1RM squat and IPFa 908, these results seem conflicting. One possible explanation is that the F group had a greater potential for improvement on IPFa 908 (preintervention mean: 107.51 6 6.96 vs. 114.85 6 13.60, in the F and FP, respectively). Although there was no statistical difference between groups for total VLd, the greater volume of full ROM squats performed by the F group may also explain the difference between groups as evidenced by the moderate correlation between full ROM squat VLd and the change in IPFa 908. Practically speaking, these data suggest that improvements in strength at the sticking point seem to be directly related to the VLd performed through the corresponding joint angles. In contrast to IPFa 908 results, FP improved IPFa 1208 by 5.7% over F, although there was no statistical interaction. Consistent with previous studies, the greater loads used during partial ROM training resulted in the ability to produce higher forces at a knee angle similar to the ROM trained (9,36,37). For applications to strength athletes, this would be advantageous for geared powerlifters who need to produce higher forces at the terminal ROM where they have less support from their gear (10). Full ROM plus partial ROM training statistically improved impulse scaled at all time points measured for both knee angles, whereas F only improved impulse scaled at 250 milliseconds with 1208 (p = 0.049). These findings seem to
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Journal of Strength and Conditioning Research agree with Clark et al. (9) who found greater improvements in isokinetic bench press peak force at 458$s21 in the terminal portion of the movement, ½ bench press throw peak force, and full bench press throw displacement in the group that trained with variable ROM over full ROM alone. As depicted in Figure 5A, the FP group achieved a larger left and upward shift in the earlier time points of the force-time curve, which has significant implications for strength-power athletes. The greater improvements in impulse scaled at earlier time points with 908 knee flexion may explain why FP improved 1RM squat although there was no statistical improvement in IPFa 908. Increased impulse scaled could be beneficial for 1RM strength because it may enhance ability to get through the sticking point. The larger left and upward shift in the force-time curve in the FP group explains the larger percent increase in impulse scaled at earlier time points (Figure 5A) and suggests RFD increased over those time periods, although no statistical difference was found for RFD in either group from pre- to postintervention. Considering the small effect sizes (,0.3) and large CVs (19.6–48.7%) for RFD at all time points, impulse scaled seems to be a better representation of changes during the early stages of isometric squat force production. In summary, partial lifts are often incorporated into resistance training programs aimed at improving maximal strength. The primary finding of our study was a trend for FP to improve over F in 1RM squat (+3.1%, d = 0.53 vs. 0.32), 1RM partial squat (+4.7%, d = 0.95 vs. 0.69), IPFa 1208 (+5.7%, d = 0.52 vs. 0.12), and impulse scaled at 50, 90, 200, and 250 milliseconds at 908 (+6.3 to 13.2%, d = 0.50–1.01 vs. 0.30–0.57) and 1208 (+3.4 to 16.8%, d = 0.45–1.11 vs. 0.08– 0.37). The FP group also trained at an overall greater relative TI, which was strongly correlated with change in 1RM squat, indicating superior adaptations. The larger effect sizes for measures of strength and explosiveness in the FP group can likely be explained the larger relative TI in the final 3 weeks of training. These findings demonstrate that partial plus full ROM training can be an effective training modality for improving maximal strength. However, further research is needed to ascertain whether combined training is more effective than full ROM training alone. Future studies on partial ROM training should include analysis of kinetic and kinematic variables during athletic movements (such as CMJ, 40-m sprint, and agility testing), longer training programs, measures of CSA with total work controlled, and different training exercises (bench press and deadlift).
PRACTICAL APPLICATIONS Partial ROM training has been proposed as an effective training modality for improving strength and power in the terminal ROM (9,36,37). These authors claim that partial ROM training more optimally loads the terminal ROM where joint angles, the force-velocity relationship, and movement patterns are more similar to those in sport.
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Although the subjects in this study were not athletes, their strength level was comparable to previous research on athletes (9,16,19). Findings of this study suggest that combined training may be more effective than full ROM training alone for improving early force-time curve characteristics. The larger effect sizes for IPFa 1208 (0.48) and impulse scaled with 1208 (0.45–1.11) in the FP group have implications for strength-power athletes. For example, the contact time for an elite sprinter is approximately 90 milliseconds, the effect size for impulse scaled at 90 milliseconds at 1208 knee angle was 0.83 vs. 0.22 in FP and F, respectively. For an elite sprinter, producing larger forces in that narrow time window may be the difference between winning vs. losing. This study also supports the use of partial ROM training as an effective means of providing variation in a training program for experienced lifters. As discussed previously, at higher training levels, variation becomes a larger component of the program design. Thus, from a practical standpoint, partial ROM training could be incorporated during a strength-speed mesocycle in preparation for a strengthpower athlete’s upcoming competition.
ACKNOWLEDGMENTS The authors confirm that there is no conflict of interest associated with this publication, and that there has been no financial support for this study that could have influenced its outcome. The authors thank the ETSU sports science students for assisting with the strength training and data collection.
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