SESSION RATINGS OF PERCEIVED EXERTION RESPONSES DURING RESISTANCE TRAINING BOUTS EQUATED FOR TOTAL WORK BUT DIFFERING IN WORK RATE JUSTIN A. KRAFT,1 JAMES M. GREEN,2 1 2
AND
KYLE R. THOMPSON1
Department of Health, Physical Education, and Recreation, Missouri Western State University, St. Joseph, Missouri; and Department of Health, Physical Education and Recreation, University of North Alabama, Florence, Alabama
ABSTRACT Kraft, JA, Green, JM, and Thompson, KR. Session ratings of perceived exertion responses during resistance training bouts equated for total work but differing in work rate. J Strength Cond Res 28(2): 540–545, 2014—Session ratings of perceived exertion (SRPE) during resistance training may be influenced by specific exercise parameters. The purpose of this study was to examine the influence of work rate (total work per unit time) and recording time on SRPE. Participants performed 3 exercise bouts of bench press, lat pulldown, overhead press, upright row, triceps extension, and biceps curl at 60% of predetermined 1 repetition maximum according to these protocols: (a) 3 sets 3 8 repetitions (reps) 3 1.5 minutes of recovery, (b) 3 sets 3 8 reps 3 3 minutes of recovery, and (c) 2 sets 3 12 reps 3 3 minutes of recovery. Session ratings of perceived exertion for the 3 3 8 3 1.5-minute recovery (5.3 6 1.8) and 2 3 12 3 3-minute recovery trials (6.2 6 1.7) were significantly greater vs. 3 3 8 3 3-minute recovery trial (4.2 6 1.8). The difference approached significance between work rate–matched protocols (p = 0.08). No difference was observed between SRPE at 15 minutes (5.1 6 1.8) vs. 30 minutes (5.2 6 1.9) post exercise. Post-set in-task ratings of perceived exertion were higher for the 2 3 12 3 3-minute recovery trial (5.9 6 1.4) vs. 3 3 8 3 1.5-minute recovery trial (4.8 6 1.2) and 3 3 8 3 3-minute recovery trial (4.0 6 1.6). The difference approached significance (p = 0.07) for the 3 3 8 3 3-minute recovery trial vs. 3 3 8 3 1.5-minute recovery trial. Session ratings of perceived exertion responded to changes in work rate with no significant difference at matched work rates, indicating that SRPE is responsive to training load. Results indicated that more proximal monitoring (15 minutes post Address correspondence to Justin A. Kraft, [email protected]. 28(2)/540–545 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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exercise) yielded reliable estimates of SRPE increasing the practical utility of the measure.
KEY WORDS RPE, weight lifting, intensity INTRODUCTION
R
esults indicate that session ratings of perceived exertion (SRPE) is a versatile marker of training load that can provide valid estimates of training loads during activities that are intermittent in nature (6,11,17–19) or that vary in technical difficulty of complex motor skills (17,18). Moreover, SRPE has been demonstrated to be sensitive to changes in intensity (measured by percentage 1 repetition maximum [1RM]) (4,16,23,25) and total work during resistance exercise training to failure (21). The sensitivity that extends to a wide variety of exercise modes is likely because ratings of perceived exertion (RPE) represents gestalt experience, reflecting a subjective estimation incorporating both physiological strain and psychological stress associated with performance of increasingly difficult tasks (2,19). As a measure of global work, SRPE constitutes the integration of multiple perceptual and physiological cues (e.g., metabolic acidosis, variation in muscle volume recruited, muscle load), which may be altered by specific exercise parameters such as intensity, volume (total work), average heart rate (HR), and work rate (25). For instance, changes in recovery period may alter physiological factors, thus altering the perceptual response (25). Green et al. (9) and Sweet et al. (25) indicated that the exercise paradigm and consequent physiological changes may mediate SRPE, yet individual mediating factors are not well understood. Session RPE presents a convenient approach to monitoring athletes. Yet to effectively use SRPE, it is critical to know how multiple factors may have an impact on the measure. Because daily training regimens frequently differ with regard to work rate (total work per unit time), it is important to elucidate how this might alter SRPE. Therefore, the primary purpose of this study was to examine the influence of work
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Journal of Strength and Conditioning Research rate on SRPE. It was hypothesized that SRPE would be sensitive to changes in work rate. Furthermore, initial research suggested 30 minutes post exercise as the appropriate period for estimating SRPE to prevent extraordinarily difficult or easy conditions at the end of exercise from dominating the rating (4,6,7,25). However, recent research has demonstrated that although SRPE recorded in the first 10 minutes after exercise differed significantly from ratings 30 minutes post exercise, values recorded at 15, 20, and 25 minutes post exercise were similar when compared with ratings 30 minutes post exercise (23). However, in that study, it is plausible that repeated reporting of the SRPE (reported every 5 minutes or 6 times in 30 minutes) may provide a confounding factor as respondents may be biased by the relative proximity of each previous measure. As such, a secondary purpose of this study was to compare SRPE estimations at 15 vs. 30 minutes post exercise. Obtaining SRPE at the earliest opportunity providing a valid assessment, which is not disrupted by acute feelings associated with final portions of the bout, has implications for optimizing the timing for recording global subjective ratings. It was hypothesized that 15-minute SRPE estimations would be confirmed as a viable time point for assessment.
METHODS Experimental Approach to the Problem
A repeated measures design was used to examine the influence of work rate (total work per unit time) on SRPE. Work rate was manipulated by equating the load (%1RM) and total volume (resistance 3 total repetitions) lifted while altering the work distribution (number of sets and repetitions per set), total recovery time between sets, and total exercise time to determine its influence on the dependent variable (SRPE). Participants completed 3 experimental trials in which they performed the bench press, lat pull down, overhead press, upright row, triceps extension, and biceps curl according to the following protocols: (a) 3 sets 3 8 repetitions (reps) 3 1.5 minutes of recovery (b) 3 sets 3 8 reps 3 3 minutes of recovery, and (c) 2 sets 3 12 reps 3 3 minutes of recovery. A standard 2-minute recovery period was allowed between exercises in all protocols. One warm-up set of 12 reps with approximately 40% of the predetermined 1RM was performed before the bench press followed by a 2-minute recovery period. No warm-up was performed before other exercises. Exercises were performed in the order listed for all protocols. Resistance was held constant at approximately 60% of the predetermined individualized 1RM, and total work volume was equated across all protocols to isolate the influence of work rate as an independent variable. Participants completed all conditions allowing for direct comparisons among protocols, and experimental trials were counterbalanced to control for ordering. Session ratings of perceived exertion were estimated 15 and 30 minutes post exercise to evaluate the potential influence of the independent variable recovery duration on the dependent variable SRPE.
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The utilization of these 3 resistance protocols allowed an assessment of the influence of work distribution (variation in number of sets and repetitions per set) and work rate (total work per unit time) on SRPE in a paradigm in which total work volume was equated among trials. A load of approximately 60% of 1RM was selected to ensure participants could complete all prescribed sets and repetitions. Literature from the National Strength and Conditioning Association regarding the load to repetition relationship suggests that participants should be able to accomplish 12 reps with a load equivalent to 67% of the 1RM and 15 reps with a load equivalent to 65% of 1RM (1). In the current paradigm, it was essential that all participants were able to complete all repetitions across multiple sets to match work rate (total weight [repetitions 3 load] per unit time). Thus, the current load was selected to allow for individual variations and to ensure all repetitions were completed while still providing a strenuous exercise bout. Subjects
Twelve, recreationally, strength-trained (strength training $2 times per week for a minimum of 6 weeks) male volunteers (age [22.2 6 2.9 years], height [177.4 6 8.4 cm], body mass [83.1 6 11.2 kg], and body fat [12.7 6 3.9%]) were recruited. A period of 6 uninterrupted weeks of training was selected to ensure that all participants met a minimum level of resistance training experience and that differences in RPE would not result from changes in strength resulting from participation in our exercise protocol. All participants received a clear explanation of the study and completed a written informed consent before participation. Procedures were approved a priori by the Missouri Western State University’s Institutional Review Board for the protection of human subjects. All participants were screened before the study for physical problems contraindicating physical activity (Physical Activity Readiness Questionnaire) (26). All subjects were nonsmokers. Volunteers were instructed to continue their normal diet (including dietary vitamins or supplements) through the duration of the study to decrease the likelihood of potential confounders resulting from nutritional changes during participation. Participants were instructed to refrain from strenuous physical activity and particularly resistance exercise and to avoid caffeine for a minimum of 24 hours before testing. Scheduling was not systematically controlled across all participants, but for each participant, an effort was made to schedule all exercise trials for the same general time of day. Procedures
On the initial visit, participants completed a health questionnaire and informed consent and were measured for descriptive data (age [years], height [centimeters], weight [kilograms], and percent body fat using an Omron body fat analyzer), and a 1RM was determined for each of the 6 exercises performed in experimental trials. Participants then returned on separate days and completed the 3 counterbalanced resistance training VOLUME 28 | NUMBER 2 | FEBRUARY 2014 |
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SRPE and Work Rate During Resistance Training protocols described above at approximately 60% of their predetermined 1RM. Heart rate (via Polar HR Monitors; Polar, Inc., Port Washington, NY, USA) and in-task ratings of RPE were measured before (pre set) and after (post set) each set. Session ratings of perceived exertion (global exercise RPE) and recovery HR were recorded 15 and 30 minutes after bout completion. Session ratings of perceived exertion were recorded at the 15- and 30-minute post exercise time interval to confirm the results of previous research (23), which indicated no significant difference in SRPE taken at 5-minute intervals between 15 and 30 minutes. All perceptual ratings were estimated according to the 10-point omni scale for resistance training (22). Pre-set RPE was a measure of perceived vigor (no actual exertion at moment recorded) and was measured by having participants respond to the question “How do you feel?” Sessions ratings of perceived exertion were estimated by asking participants the question, “How was your workout?” (5). This variable provides a subjective estimate of the global difficulty of the entire exercise bout.
(trial) repeated measures ANOVA was used to assess SRPE differences among the 3 exercise protocols. This would reflect potential differences in subjective responses in trials where work rate (but not work volume) was different, directly testing the hypothesis that SRPE would be altered with work rate. Because SRPE estimated at 30 minutes is well accepted in previous literature, these values (rather than SRPE estimations at 15 minutes) were used for that analysis. At points where follow-up tests were required, a Bonferroni’s procedure (14) was used. To determine the appropriateness of estimating SRPE at 15 minutes post exercise (vs. 30 minutes), a paired t-test was used to detect differences in SRPE estimated 15 minutes post exercise vs. 30 minutes post exercise. This analysis tested the hypothesis that 15 minutes is a viable time point for assessment of SRPE after training. A paired t-test was additionally used to analyze differences in recovery HR at 15 and 30 minutes post exercise. Differences were considered significant at the level of p # 0.05 (2-tailed test).
One Repetition Maximum Determination
Pre- and post-set measures are presented in Table 1. Pre-set RPE was significantly lower with extended recovery period when doing the same number of sets and repetitions per set. Post-set RPE was significantly higher for the 2 3 12 3 3-minute recovery trial vs. 3 3 8 3 1.5-minute recovery trial despite matched work rates. Post-set RPE was significantly lower for 3 3 8 3 3-minute recovery trial vs. the 2 3 12 3 3-minute recovery trial and the difference approached significance (p = 0.07) vs. 3 3 8 3 1.5-minute recovery trial. Pre-set HR for the 3 3 8 3 1.5-minute recovery trial was significantly higher than the 3 3 8 3 3-minute recovery trial. No other significant differences in pre-set or post-set HR were observed. Session ratings of perceived exertion for the 3 3 8 3 1.5-minute recovery (5.3 6 1.8) and 2 3 12 3 3-minute recovery trials (6.2 6 1.7) were significantly higher vs. 3 3 8 3 3-minute recovery trial (4.2 6 1.8). The difference approached significance for the 3 3 8 3 1.5-minute recovery vs. the 2 3 12 3 3-minute recovery trial (p = 0.08) despite matched work rates. No significant difference in SRPE was
Exercises were performed in the order listed above. The 1RM was defined as the heaviest weight the participant was able to lift for 1 complete repetition (23). Determination of the 1RM was performed according to the procedure outlined by the National Strength and Conditioning Association (1). Participants performed a light warm-up with a resistance they estimated they could lift 5–10 times. After a 1-minute recovery, the participant performed a second warm-up using a weight they estimated they could lift 3–5 times. A 2-minute recovery was provided. At this time, the participant estimated a nearmaximal load (one they expected to perform 2 or 3 times) and performed the final warm-up followed by a 3-minute recovery. The load was increased to an estimated maximum (added 10–20 lb for upper body), and a 1RM was attempted. If successful, a 3-minute recovery was provided and an additional attempt was made with a new estimated weight. If unsuccessful, a 3-minute recovery was provided and another attempt was made with a reduced load. Loads were adjusted based on participant feedback with the goal of identifying the 1RM within 3–5 attempts. A 3-minute recovery was allowed between exercises.
RESULTS
TABLE 1. Pre and post-set RPE and heart rate by resistance protocol.z
Statistical Analyses
Statistical analysis was completed using PASW Statistics software. A series of 6 (exercise) 3 3 (condition) repeated measures analyses of variance (ANOVAs) were used to detect differences among trials for dependent measures of pre-set RPE, post-set RPE, pre-set HR, and post-set HR. A 1-factor
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Protocol (sets 3 reps 3 min) 3 3 8 3 1.5 rest 3 3 8 3 3 rest 2 3 12 3 3 rest
Pre-set RPE
Post-set RPE
Pre-set HR
Post-set HR
3.1 6 1.6 2.5 6 1.6* 3.6 6 1.6
4.8 6 1.2 4.0 6 1.6**† 5.9 6 1.4*
95 6 10 89 6 10* 91 6 8
128 6 13 126 6 10 134 6 11
zRPE = ratings of perceived exertion; HR = heart rate; rep = repetition. *p , 0.05 vs. 3 sets 3 8 reps 3 1.5 minutes of rest. **p , 0.05 vs. 2 sets 3 12 reps 3 3 minutes of rest. †p = 0.07 for 3 sets 3 8 reps 3 1.5 minutes rest vs. 3 sets 3 8 reps 3 3 minutes of rest.
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Journal of Strength and Conditioning Research observed between mean SRPE estimated 15 minutes post exercise (5.1 6 1.8) vs. 30 minutes post exercise (5.2 6 1.9) (r = 0.986; p , 0.05), although mean recovery HR was significantly higher (81 6 8 b$min21) at 15 minutes post exercise than 30 minutes post exercise (74 6 6 b$min21) (r = 0.798; p , 0.05).
DISCUSSION The current study examined the influence of work rate in a resistance training paradigm while also comparing SRPE estimations at 15 vs. 30 minutes post exercise. Session ratings of perceived exertion were responsive to changes in work rate with higher SRPE exhibited during the work rate–matched (3 3 8 3 1.5-minute recovery and 2 3 12 3 3-minute recovery) protocols vs. the 3 3 8 3 3-minute recovery protocol. No difference was observed when work rate was matched, indicating that SRPE may be linked more tightly with work rate than the number of sets or repetitions per set. However, the difference in SRPE approached significance (p = 0.08) between protocols matched for work rate, indicating an interaction with other potentially mediating effects that warrant further investigation. While providing novel information, current results are in agreement with the consensus that perceptual responses to exercise (whether acute or global) result from multiple factors rather than any single dominant input signal (2,9). To isolate the effects of work rate, resistance was held constant (at 60% of the 1RM) throughout all protocols and total work volume was equated among resistance training trials. The influence of varying resistance on SRPE has been evaluated, and SRPE has been demonstrated to be responsive to changes of intensity and to increase when exercise is performed at increasing percentages of 1RM (4,23,25). It should be noted that exercises were performed to a specified number of repetitions, and total work volume was not equated in these studies. On the other hand, Pritchett et al. (21) found that participants completed a greater total volume of work and reported higher SRPE at lower relative intensities (percentage of 1RM) during resistance training. In the study of Pritchett et al. (21), participants completed trials at 60 and 90% of 1RM but to volitional exhaustion at each resistance. Results led authors to conclude that SRPE depends more on the total work than on relative intensity, which contradicted previous findings (4,25). Still, none of the aforementioned studies controlled work rate. Green et al. (9) concluded that SRPE was significantly greater after an interval cycling paradigm vs. a constant load cycling bout with equated work volume. The conclusion from that study was that the greater disruption in homeostasis during interval exercise, reflected by elevated blood lactate, accounted in part for systematically increased SRPE. It is plausible that the same concept is implicated in a resistance training paradigm. The current study has indicated that work rate may also influence SRPE, potentially accounting for a proportion of the variance at differing intensity levels. However, it is plausible that exercise protocols that vary in number of
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repetitions per sets and recovery period duration may routinely vary in load and this is worthy of future inquiry. Therefore, future research examining the interaction of varied work distributions (i.e., altered load, repetition distribution, and set distribution) should control both work volume and work rate to enhance insight regarding the mediating factors for SRPE across exercise bouts comprising differing physiological parameters. Additionally, future studies may include more direct attempts at assessing the disruption in homeostasis as a result of varying training protocols in an attempt to determine mechanisms associated with changes in perceptual responses. Post-set RPE was higher for the high repetition exercise protocol (2 3 12 3 3-minute recovery) vs. the 3 3 8 3 3-minute recovery protocol and the matched work rate protocol (3 3 8 3 1.5-minute recovery). This is consistent with Pritchett et al. (21) and likely resulted from completing more total work per set in this protocol. It is plausible that this protocol could have resulted in greater disruption in homeostasis (acid–base imbalance, etc), eliciting altered perceptual responses. It is emphasized that direct evidence regarding this notion is lacking in the current investigation, and therefore, any such conclusions at current would be speculative. Higher post-set RPE did not seem to influence the SRPE when work rate was controlled, as indicated by the lack of significant difference in SRPE between protocols matched for work rate. These findings are consistent with previous studies indicating SRPE estimations and acute RPE responses that averaged across time do not correspond and provide different information (15,23). This is logical because of the intermittent nature of effort during resistance training. Still, it is worth noting that the SRPE difference between work rate–matched protocols did approach statistical significance (2 3 12 3 3-minute recovery vs. 3 3 8 3 1.5-minute recovery [p = 0.08]), indicating that the difficulty of individual sets (i.e., work distribution parameters) may contribute to the overall gestalt experience reflected in SRPE. We hypothesize that the acute load may provide a strong cue for acute perceptual responses during resistance training when the termination point for a set is a predetermined number rather than volitional exhaustion. That is, it is plausible that a participant would gage the feelings of heaviness of a lift rather than the feelings of exertion prompted by the lift. This may be supported by lack of correspondence between results from Pritchett et al. (21), where greater perceptual responses were observed at a lower relative intensity (60 vs. 90% of 1RM) when compared with Day et al. (4) and Sweet et al. (25), where perceptual responses increased concurrently with %1RM lifted. In the current study, the relative load was clamped at 60% of 1RM, which again eliminated the possibility of perceptual responses being altered because of different loads and isolated the potential impact of work rate as desired. Using this approach and interpreting current results with regard to previous investigations leads to the conclusion that work rate does, in the current paradigm, VOLUME 28 | NUMBER 2 | FEBRUARY 2014 |
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SRPE and Work Rate During Resistance Training alter global perceptual responses. Further work is of course warranted to assess this notion in other modes of resistance training (e.g., circuit training) and under different relative loads (i.e., greater than 60% 1RM). Pre-set RPE did not differ in trials, which controlled work rate. However, it decreased as work rate decreased. This result is inconsistent with previous findings that reported no difference in pre-set RPE during a 4-set squat protocol using 3 different recovery intervals (13). Current results also indicated a trend (difference approached significance 3 3 8 3 3-minute recovery vs. 3 3 8 3 1.5-minute recovery, p = 0.07) of increased post-set RPE with shortened recovery period. This trend is discordant with previous findings that indicated no significant difference in RPE during a 3-set knee extension protocol with recovery interval varying from 1 to 3 minutes (28) or during a 4-set 3 20-rep isokinetic quadriceps exercise with either 40 or 160 seconds of recovery (20). In all cases, discordant findings may be attributable in part to inherent differences between a single exercise protocol and the multiexercise protocol used in the current study. Additionally, participants in the study of Pincivero et al. (20) completed more total work when the recovery period was extended, whereas total work per set was constant in the current study (3 3 8 3 3-minute recovery vs. 3 3 8 3 1.5-minute recovery with constant resistance). Preand post-set HRs were similar across the exercise bout when work rate was matched. As expected, pre-set HR was lower with reduced work rate when completing the same number of sets and repetitions. As indicated, previous research has suggested that acute disruptions in homeostasis are likely to alter perceptual responses (9) and it is reasonable that the exercise paradigm including the recovery periods and work rates should be considered as potential factors altering perceptual responses. Session ratings of perceived exertion have been shown to differ when taken 5 and 10 minutes post exercise vs. 30 minutes post exercise with no difference in measures taken 15 minutes post exercise or later vs. 30 minutes post exercise, indicating the SRPE measure becomes more stable after a minimal passage time (23) and may be influenced less by the strain experienced during terminal portions of the workout. The current lack of observed difference and significant correlation (r = 0.986) in SRPE when recorded 15 minutes post exercise vs. 30 minutes post exercise corresponds with Singh et al. (23) corroborating that 15 minutes post exercise is a sufficient passage of time for the estimation of SRPE. It has been recommended that SRPE should be estimated 30 minutes post exercise to prevent extraordinarily difficult or easy conditions at the end of exercise from dominating the rating (4,6,7,25). Practically speaking, these findings indicate a reduction in monitoring time required by coaches and practitioners compared with the previously postulated 30 minutes before estimation of SRPE. Lack of observed differences in SRPE despite differences in recovery HR (15 minutes vs. 30 minutes post exercise) indicates that
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SRPE obtained 15 minutes post exercise is estimated independently of recovery HR. This is further supported by Hornsby et al. (10) who showed no effect of terminal acute RPE on SRPE.
PRACTICAL APPLICATIONS The ability to validly assess training load is essential to monitoring periodization programs and promoting maximal training benefit (3,27). Although valid assessment is required, highly technical measures requiring invasive techniques are often objectionable, time consuming, difficult to obtain, and entirely impractical for daily monitoring. Perceptual responses are subjectively based and offer a convenient alternative. However, such measures must be shown valid to be acceptable and influential factors must be thoroughly understood for perceptually based evaluations to demonstrate optimal utility. Previous studies indicate acceptable validity (4,8,12,24), yet because perceived exertion responses reflect feelings based on a multitude of physiological and psychological factors, it is critical to extend the understanding of how these subjectively based assessments are altered when training design is altered. From a practical application standpoint, a deeper understanding of the stability of the SRPE response to varying exercise parameters during resistance training will allow coaches and practitioners to more effectively assess training regimen efficacy. Previous findings indicate that total work volume may be a more important factor than intensity (as a percentage of 1RM) in determining session training load (21). Current results indicate that SRPE is more closely linked to work rate than the number of sets and repetitions per set. As such, results indicate that coaches and practitioners using SRPE as an adjunct to monitoring training can, in general, have confidence that the SRPE is a sensitive measure of training load that will reflect differences in work rate. However, because of the gestalt nature of perceptual responses, it would be inaccurate to deduce from current results that work rate is the principle factor mediating SRPE. Session ratings of perceived exertion become more stable with a minimal passage of time (23). Research recommends obtaining SRPE 30 minutes post exercise (4,6,7,25). However, in many settings, this time restriction may provide a practical barrier to usage. Current results support the notion that coaches, trainers, and athletes can have confidence in SRPE estimations recorded 15 minutes post exercise and need not wait for the previously recommended 30-minute recovery before assessing SRPE. Shorter monitoring times before assessment may increase SRPE utility for coaches and practitioners, thereby further enhancing the convenience and practicality of SRPE.
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28. Woods, S, Bridge, T, Nelson, D, Risse, K, and Pincivero, DM. The effects of rest interval length on ratings of perceived exertion during dynamic knee extension exercise. J Strength Cond Res 18: 540–545, 2004.
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KYLE R. THOMPSON1
Department of Health, Physical Education, and Recreation, Missouri Western State University, St. Joseph, Missouri; and Department of Health, Physical Education and Recreation, University of North Alabama, Florence, Alabama
ABSTRACT Kraft, JA, Green, JM, and Thompson, KR. Session ratings of perceived exertion responses during resistance training bouts equated for total work but differing in work rate. J Strength Cond Res 28(2): 540–545, 2014—Session ratings of perceived exertion (SRPE) during resistance training may be influenced by specific exercise parameters. The purpose of this study was to examine the influence of work rate (total work per unit time) and recording time on SRPE. Participants performed 3 exercise bouts of bench press, lat pulldown, overhead press, upright row, triceps extension, and biceps curl at 60% of predetermined 1 repetition maximum according to these protocols: (a) 3 sets 3 8 repetitions (reps) 3 1.5 minutes of recovery, (b) 3 sets 3 8 reps 3 3 minutes of recovery, and (c) 2 sets 3 12 reps 3 3 minutes of recovery. Session ratings of perceived exertion for the 3 3 8 3 1.5-minute recovery (5.3 6 1.8) and 2 3 12 3 3-minute recovery trials (6.2 6 1.7) were significantly greater vs. 3 3 8 3 3-minute recovery trial (4.2 6 1.8). The difference approached significance between work rate–matched protocols (p = 0.08). No difference was observed between SRPE at 15 minutes (5.1 6 1.8) vs. 30 minutes (5.2 6 1.9) post exercise. Post-set in-task ratings of perceived exertion were higher for the 2 3 12 3 3-minute recovery trial (5.9 6 1.4) vs. 3 3 8 3 1.5-minute recovery trial (4.8 6 1.2) and 3 3 8 3 3-minute recovery trial (4.0 6 1.6). The difference approached significance (p = 0.07) for the 3 3 8 3 3-minute recovery trial vs. 3 3 8 3 1.5-minute recovery trial. Session ratings of perceived exertion responded to changes in work rate with no significant difference at matched work rates, indicating that SRPE is responsive to training load. Results indicated that more proximal monitoring (15 minutes post Address correspondence to Justin A. Kraft, [email protected]. 28(2)/540–545 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
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exercise) yielded reliable estimates of SRPE increasing the practical utility of the measure.
KEY WORDS RPE, weight lifting, intensity INTRODUCTION
R
esults indicate that session ratings of perceived exertion (SRPE) is a versatile marker of training load that can provide valid estimates of training loads during activities that are intermittent in nature (6,11,17–19) or that vary in technical difficulty of complex motor skills (17,18). Moreover, SRPE has been demonstrated to be sensitive to changes in intensity (measured by percentage 1 repetition maximum [1RM]) (4,16,23,25) and total work during resistance exercise training to failure (21). The sensitivity that extends to a wide variety of exercise modes is likely because ratings of perceived exertion (RPE) represents gestalt experience, reflecting a subjective estimation incorporating both physiological strain and psychological stress associated with performance of increasingly difficult tasks (2,19). As a measure of global work, SRPE constitutes the integration of multiple perceptual and physiological cues (e.g., metabolic acidosis, variation in muscle volume recruited, muscle load), which may be altered by specific exercise parameters such as intensity, volume (total work), average heart rate (HR), and work rate (25). For instance, changes in recovery period may alter physiological factors, thus altering the perceptual response (25). Green et al. (9) and Sweet et al. (25) indicated that the exercise paradigm and consequent physiological changes may mediate SRPE, yet individual mediating factors are not well understood. Session RPE presents a convenient approach to monitoring athletes. Yet to effectively use SRPE, it is critical to know how multiple factors may have an impact on the measure. Because daily training regimens frequently differ with regard to work rate (total work per unit time), it is important to elucidate how this might alter SRPE. Therefore, the primary purpose of this study was to examine the influence of work
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Journal of Strength and Conditioning Research rate on SRPE. It was hypothesized that SRPE would be sensitive to changes in work rate. Furthermore, initial research suggested 30 minutes post exercise as the appropriate period for estimating SRPE to prevent extraordinarily difficult or easy conditions at the end of exercise from dominating the rating (4,6,7,25). However, recent research has demonstrated that although SRPE recorded in the first 10 minutes after exercise differed significantly from ratings 30 minutes post exercise, values recorded at 15, 20, and 25 minutes post exercise were similar when compared with ratings 30 minutes post exercise (23). However, in that study, it is plausible that repeated reporting of the SRPE (reported every 5 minutes or 6 times in 30 minutes) may provide a confounding factor as respondents may be biased by the relative proximity of each previous measure. As such, a secondary purpose of this study was to compare SRPE estimations at 15 vs. 30 minutes post exercise. Obtaining SRPE at the earliest opportunity providing a valid assessment, which is not disrupted by acute feelings associated with final portions of the bout, has implications for optimizing the timing for recording global subjective ratings. It was hypothesized that 15-minute SRPE estimations would be confirmed as a viable time point for assessment.
METHODS Experimental Approach to the Problem
A repeated measures design was used to examine the influence of work rate (total work per unit time) on SRPE. Work rate was manipulated by equating the load (%1RM) and total volume (resistance 3 total repetitions) lifted while altering the work distribution (number of sets and repetitions per set), total recovery time between sets, and total exercise time to determine its influence on the dependent variable (SRPE). Participants completed 3 experimental trials in which they performed the bench press, lat pull down, overhead press, upright row, triceps extension, and biceps curl according to the following protocols: (a) 3 sets 3 8 repetitions (reps) 3 1.5 minutes of recovery (b) 3 sets 3 8 reps 3 3 minutes of recovery, and (c) 2 sets 3 12 reps 3 3 minutes of recovery. A standard 2-minute recovery period was allowed between exercises in all protocols. One warm-up set of 12 reps with approximately 40% of the predetermined 1RM was performed before the bench press followed by a 2-minute recovery period. No warm-up was performed before other exercises. Exercises were performed in the order listed for all protocols. Resistance was held constant at approximately 60% of the predetermined individualized 1RM, and total work volume was equated across all protocols to isolate the influence of work rate as an independent variable. Participants completed all conditions allowing for direct comparisons among protocols, and experimental trials were counterbalanced to control for ordering. Session ratings of perceived exertion were estimated 15 and 30 minutes post exercise to evaluate the potential influence of the independent variable recovery duration on the dependent variable SRPE.
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The utilization of these 3 resistance protocols allowed an assessment of the influence of work distribution (variation in number of sets and repetitions per set) and work rate (total work per unit time) on SRPE in a paradigm in which total work volume was equated among trials. A load of approximately 60% of 1RM was selected to ensure participants could complete all prescribed sets and repetitions. Literature from the National Strength and Conditioning Association regarding the load to repetition relationship suggests that participants should be able to accomplish 12 reps with a load equivalent to 67% of the 1RM and 15 reps with a load equivalent to 65% of 1RM (1). In the current paradigm, it was essential that all participants were able to complete all repetitions across multiple sets to match work rate (total weight [repetitions 3 load] per unit time). Thus, the current load was selected to allow for individual variations and to ensure all repetitions were completed while still providing a strenuous exercise bout. Subjects
Twelve, recreationally, strength-trained (strength training $2 times per week for a minimum of 6 weeks) male volunteers (age [22.2 6 2.9 years], height [177.4 6 8.4 cm], body mass [83.1 6 11.2 kg], and body fat [12.7 6 3.9%]) were recruited. A period of 6 uninterrupted weeks of training was selected to ensure that all participants met a minimum level of resistance training experience and that differences in RPE would not result from changes in strength resulting from participation in our exercise protocol. All participants received a clear explanation of the study and completed a written informed consent before participation. Procedures were approved a priori by the Missouri Western State University’s Institutional Review Board for the protection of human subjects. All participants were screened before the study for physical problems contraindicating physical activity (Physical Activity Readiness Questionnaire) (26). All subjects were nonsmokers. Volunteers were instructed to continue their normal diet (including dietary vitamins or supplements) through the duration of the study to decrease the likelihood of potential confounders resulting from nutritional changes during participation. Participants were instructed to refrain from strenuous physical activity and particularly resistance exercise and to avoid caffeine for a minimum of 24 hours before testing. Scheduling was not systematically controlled across all participants, but for each participant, an effort was made to schedule all exercise trials for the same general time of day. Procedures
On the initial visit, participants completed a health questionnaire and informed consent and were measured for descriptive data (age [years], height [centimeters], weight [kilograms], and percent body fat using an Omron body fat analyzer), and a 1RM was determined for each of the 6 exercises performed in experimental trials. Participants then returned on separate days and completed the 3 counterbalanced resistance training VOLUME 28 | NUMBER 2 | FEBRUARY 2014 |
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SRPE and Work Rate During Resistance Training protocols described above at approximately 60% of their predetermined 1RM. Heart rate (via Polar HR Monitors; Polar, Inc., Port Washington, NY, USA) and in-task ratings of RPE were measured before (pre set) and after (post set) each set. Session ratings of perceived exertion (global exercise RPE) and recovery HR were recorded 15 and 30 minutes after bout completion. Session ratings of perceived exertion were recorded at the 15- and 30-minute post exercise time interval to confirm the results of previous research (23), which indicated no significant difference in SRPE taken at 5-minute intervals between 15 and 30 minutes. All perceptual ratings were estimated according to the 10-point omni scale for resistance training (22). Pre-set RPE was a measure of perceived vigor (no actual exertion at moment recorded) and was measured by having participants respond to the question “How do you feel?” Sessions ratings of perceived exertion were estimated by asking participants the question, “How was your workout?” (5). This variable provides a subjective estimate of the global difficulty of the entire exercise bout.
(trial) repeated measures ANOVA was used to assess SRPE differences among the 3 exercise protocols. This would reflect potential differences in subjective responses in trials where work rate (but not work volume) was different, directly testing the hypothesis that SRPE would be altered with work rate. Because SRPE estimated at 30 minutes is well accepted in previous literature, these values (rather than SRPE estimations at 15 minutes) were used for that analysis. At points where follow-up tests were required, a Bonferroni’s procedure (14) was used. To determine the appropriateness of estimating SRPE at 15 minutes post exercise (vs. 30 minutes), a paired t-test was used to detect differences in SRPE estimated 15 minutes post exercise vs. 30 minutes post exercise. This analysis tested the hypothesis that 15 minutes is a viable time point for assessment of SRPE after training. A paired t-test was additionally used to analyze differences in recovery HR at 15 and 30 minutes post exercise. Differences were considered significant at the level of p # 0.05 (2-tailed test).
One Repetition Maximum Determination
Pre- and post-set measures are presented in Table 1. Pre-set RPE was significantly lower with extended recovery period when doing the same number of sets and repetitions per set. Post-set RPE was significantly higher for the 2 3 12 3 3-minute recovery trial vs. 3 3 8 3 1.5-minute recovery trial despite matched work rates. Post-set RPE was significantly lower for 3 3 8 3 3-minute recovery trial vs. the 2 3 12 3 3-minute recovery trial and the difference approached significance (p = 0.07) vs. 3 3 8 3 1.5-minute recovery trial. Pre-set HR for the 3 3 8 3 1.5-minute recovery trial was significantly higher than the 3 3 8 3 3-minute recovery trial. No other significant differences in pre-set or post-set HR were observed. Session ratings of perceived exertion for the 3 3 8 3 1.5-minute recovery (5.3 6 1.8) and 2 3 12 3 3-minute recovery trials (6.2 6 1.7) were significantly higher vs. 3 3 8 3 3-minute recovery trial (4.2 6 1.8). The difference approached significance for the 3 3 8 3 1.5-minute recovery vs. the 2 3 12 3 3-minute recovery trial (p = 0.08) despite matched work rates. No significant difference in SRPE was
Exercises were performed in the order listed above. The 1RM was defined as the heaviest weight the participant was able to lift for 1 complete repetition (23). Determination of the 1RM was performed according to the procedure outlined by the National Strength and Conditioning Association (1). Participants performed a light warm-up with a resistance they estimated they could lift 5–10 times. After a 1-minute recovery, the participant performed a second warm-up using a weight they estimated they could lift 3–5 times. A 2-minute recovery was provided. At this time, the participant estimated a nearmaximal load (one they expected to perform 2 or 3 times) and performed the final warm-up followed by a 3-minute recovery. The load was increased to an estimated maximum (added 10–20 lb for upper body), and a 1RM was attempted. If successful, a 3-minute recovery was provided and an additional attempt was made with a new estimated weight. If unsuccessful, a 3-minute recovery was provided and another attempt was made with a reduced load. Loads were adjusted based on participant feedback with the goal of identifying the 1RM within 3–5 attempts. A 3-minute recovery was allowed between exercises.
RESULTS
TABLE 1. Pre and post-set RPE and heart rate by resistance protocol.z
Statistical Analyses
Statistical analysis was completed using PASW Statistics software. A series of 6 (exercise) 3 3 (condition) repeated measures analyses of variance (ANOVAs) were used to detect differences among trials for dependent measures of pre-set RPE, post-set RPE, pre-set HR, and post-set HR. A 1-factor
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Protocol (sets 3 reps 3 min) 3 3 8 3 1.5 rest 3 3 8 3 3 rest 2 3 12 3 3 rest
Pre-set RPE
Post-set RPE
Pre-set HR
Post-set HR
3.1 6 1.6 2.5 6 1.6* 3.6 6 1.6
4.8 6 1.2 4.0 6 1.6**† 5.9 6 1.4*
95 6 10 89 6 10* 91 6 8
128 6 13 126 6 10 134 6 11
zRPE = ratings of perceived exertion; HR = heart rate; rep = repetition. *p , 0.05 vs. 3 sets 3 8 reps 3 1.5 minutes of rest. **p , 0.05 vs. 2 sets 3 12 reps 3 3 minutes of rest. †p = 0.07 for 3 sets 3 8 reps 3 1.5 minutes rest vs. 3 sets 3 8 reps 3 3 minutes of rest.
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Journal of Strength and Conditioning Research observed between mean SRPE estimated 15 minutes post exercise (5.1 6 1.8) vs. 30 minutes post exercise (5.2 6 1.9) (r = 0.986; p , 0.05), although mean recovery HR was significantly higher (81 6 8 b$min21) at 15 minutes post exercise than 30 minutes post exercise (74 6 6 b$min21) (r = 0.798; p , 0.05).
DISCUSSION The current study examined the influence of work rate in a resistance training paradigm while also comparing SRPE estimations at 15 vs. 30 minutes post exercise. Session ratings of perceived exertion were responsive to changes in work rate with higher SRPE exhibited during the work rate–matched (3 3 8 3 1.5-minute recovery and 2 3 12 3 3-minute recovery) protocols vs. the 3 3 8 3 3-minute recovery protocol. No difference was observed when work rate was matched, indicating that SRPE may be linked more tightly with work rate than the number of sets or repetitions per set. However, the difference in SRPE approached significance (p = 0.08) between protocols matched for work rate, indicating an interaction with other potentially mediating effects that warrant further investigation. While providing novel information, current results are in agreement with the consensus that perceptual responses to exercise (whether acute or global) result from multiple factors rather than any single dominant input signal (2,9). To isolate the effects of work rate, resistance was held constant (at 60% of the 1RM) throughout all protocols and total work volume was equated among resistance training trials. The influence of varying resistance on SRPE has been evaluated, and SRPE has been demonstrated to be responsive to changes of intensity and to increase when exercise is performed at increasing percentages of 1RM (4,23,25). It should be noted that exercises were performed to a specified number of repetitions, and total work volume was not equated in these studies. On the other hand, Pritchett et al. (21) found that participants completed a greater total volume of work and reported higher SRPE at lower relative intensities (percentage of 1RM) during resistance training. In the study of Pritchett et al. (21), participants completed trials at 60 and 90% of 1RM but to volitional exhaustion at each resistance. Results led authors to conclude that SRPE depends more on the total work than on relative intensity, which contradicted previous findings (4,25). Still, none of the aforementioned studies controlled work rate. Green et al. (9) concluded that SRPE was significantly greater after an interval cycling paradigm vs. a constant load cycling bout with equated work volume. The conclusion from that study was that the greater disruption in homeostasis during interval exercise, reflected by elevated blood lactate, accounted in part for systematically increased SRPE. It is plausible that the same concept is implicated in a resistance training paradigm. The current study has indicated that work rate may also influence SRPE, potentially accounting for a proportion of the variance at differing intensity levels. However, it is plausible that exercise protocols that vary in number of
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repetitions per sets and recovery period duration may routinely vary in load and this is worthy of future inquiry. Therefore, future research examining the interaction of varied work distributions (i.e., altered load, repetition distribution, and set distribution) should control both work volume and work rate to enhance insight regarding the mediating factors for SRPE across exercise bouts comprising differing physiological parameters. Additionally, future studies may include more direct attempts at assessing the disruption in homeostasis as a result of varying training protocols in an attempt to determine mechanisms associated with changes in perceptual responses. Post-set RPE was higher for the high repetition exercise protocol (2 3 12 3 3-minute recovery) vs. the 3 3 8 3 3-minute recovery protocol and the matched work rate protocol (3 3 8 3 1.5-minute recovery). This is consistent with Pritchett et al. (21) and likely resulted from completing more total work per set in this protocol. It is plausible that this protocol could have resulted in greater disruption in homeostasis (acid–base imbalance, etc), eliciting altered perceptual responses. It is emphasized that direct evidence regarding this notion is lacking in the current investigation, and therefore, any such conclusions at current would be speculative. Higher post-set RPE did not seem to influence the SRPE when work rate was controlled, as indicated by the lack of significant difference in SRPE between protocols matched for work rate. These findings are consistent with previous studies indicating SRPE estimations and acute RPE responses that averaged across time do not correspond and provide different information (15,23). This is logical because of the intermittent nature of effort during resistance training. Still, it is worth noting that the SRPE difference between work rate–matched protocols did approach statistical significance (2 3 12 3 3-minute recovery vs. 3 3 8 3 1.5-minute recovery [p = 0.08]), indicating that the difficulty of individual sets (i.e., work distribution parameters) may contribute to the overall gestalt experience reflected in SRPE. We hypothesize that the acute load may provide a strong cue for acute perceptual responses during resistance training when the termination point for a set is a predetermined number rather than volitional exhaustion. That is, it is plausible that a participant would gage the feelings of heaviness of a lift rather than the feelings of exertion prompted by the lift. This may be supported by lack of correspondence between results from Pritchett et al. (21), where greater perceptual responses were observed at a lower relative intensity (60 vs. 90% of 1RM) when compared with Day et al. (4) and Sweet et al. (25), where perceptual responses increased concurrently with %1RM lifted. In the current study, the relative load was clamped at 60% of 1RM, which again eliminated the possibility of perceptual responses being altered because of different loads and isolated the potential impact of work rate as desired. Using this approach and interpreting current results with regard to previous investigations leads to the conclusion that work rate does, in the current paradigm, VOLUME 28 | NUMBER 2 | FEBRUARY 2014 |
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SRPE and Work Rate During Resistance Training alter global perceptual responses. Further work is of course warranted to assess this notion in other modes of resistance training (e.g., circuit training) and under different relative loads (i.e., greater than 60% 1RM). Pre-set RPE did not differ in trials, which controlled work rate. However, it decreased as work rate decreased. This result is inconsistent with previous findings that reported no difference in pre-set RPE during a 4-set squat protocol using 3 different recovery intervals (13). Current results also indicated a trend (difference approached significance 3 3 8 3 3-minute recovery vs. 3 3 8 3 1.5-minute recovery, p = 0.07) of increased post-set RPE with shortened recovery period. This trend is discordant with previous findings that indicated no significant difference in RPE during a 3-set knee extension protocol with recovery interval varying from 1 to 3 minutes (28) or during a 4-set 3 20-rep isokinetic quadriceps exercise with either 40 or 160 seconds of recovery (20). In all cases, discordant findings may be attributable in part to inherent differences between a single exercise protocol and the multiexercise protocol used in the current study. Additionally, participants in the study of Pincivero et al. (20) completed more total work when the recovery period was extended, whereas total work per set was constant in the current study (3 3 8 3 3-minute recovery vs. 3 3 8 3 1.5-minute recovery with constant resistance). Preand post-set HRs were similar across the exercise bout when work rate was matched. As expected, pre-set HR was lower with reduced work rate when completing the same number of sets and repetitions. As indicated, previous research has suggested that acute disruptions in homeostasis are likely to alter perceptual responses (9) and it is reasonable that the exercise paradigm including the recovery periods and work rates should be considered as potential factors altering perceptual responses. Session ratings of perceived exertion have been shown to differ when taken 5 and 10 minutes post exercise vs. 30 minutes post exercise with no difference in measures taken 15 minutes post exercise or later vs. 30 minutes post exercise, indicating the SRPE measure becomes more stable after a minimal passage time (23) and may be influenced less by the strain experienced during terminal portions of the workout. The current lack of observed difference and significant correlation (r = 0.986) in SRPE when recorded 15 minutes post exercise vs. 30 minutes post exercise corresponds with Singh et al. (23) corroborating that 15 minutes post exercise is a sufficient passage of time for the estimation of SRPE. It has been recommended that SRPE should be estimated 30 minutes post exercise to prevent extraordinarily difficult or easy conditions at the end of exercise from dominating the rating (4,6,7,25). Practically speaking, these findings indicate a reduction in monitoring time required by coaches and practitioners compared with the previously postulated 30 minutes before estimation of SRPE. Lack of observed differences in SRPE despite differences in recovery HR (15 minutes vs. 30 minutes post exercise) indicates that
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SRPE obtained 15 minutes post exercise is estimated independently of recovery HR. This is further supported by Hornsby et al. (10) who showed no effect of terminal acute RPE on SRPE.
PRACTICAL APPLICATIONS The ability to validly assess training load is essential to monitoring periodization programs and promoting maximal training benefit (3,27). Although valid assessment is required, highly technical measures requiring invasive techniques are often objectionable, time consuming, difficult to obtain, and entirely impractical for daily monitoring. Perceptual responses are subjectively based and offer a convenient alternative. However, such measures must be shown valid to be acceptable and influential factors must be thoroughly understood for perceptually based evaluations to demonstrate optimal utility. Previous studies indicate acceptable validity (4,8,12,24), yet because perceived exertion responses reflect feelings based on a multitude of physiological and psychological factors, it is critical to extend the understanding of how these subjectively based assessments are altered when training design is altered. From a practical application standpoint, a deeper understanding of the stability of the SRPE response to varying exercise parameters during resistance training will allow coaches and practitioners to more effectively assess training regimen efficacy. Previous findings indicate that total work volume may be a more important factor than intensity (as a percentage of 1RM) in determining session training load (21). Current results indicate that SRPE is more closely linked to work rate than the number of sets and repetitions per set. As such, results indicate that coaches and practitioners using SRPE as an adjunct to monitoring training can, in general, have confidence that the SRPE is a sensitive measure of training load that will reflect differences in work rate. However, because of the gestalt nature of perceptual responses, it would be inaccurate to deduce from current results that work rate is the principle factor mediating SRPE. Session ratings of perceived exertion become more stable with a minimal passage of time (23). Research recommends obtaining SRPE 30 minutes post exercise (4,6,7,25). However, in many settings, this time restriction may provide a practical barrier to usage. Current results support the notion that coaches, trainers, and athletes can have confidence in SRPE estimations recorded 15 minutes post exercise and need not wait for the previously recommended 30-minute recovery before assessing SRPE. Shorter monitoring times before assessment may increase SRPE utility for coaches and practitioners, thereby further enhancing the convenience and practicality of SRPE.
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