VIBRATION EXERCISE AS A WARM-UP MODALITY DEADLIFT POWER OUTPUT DARRYL J. COCHRANE,1 KARL W. COLEY,1 HAYDEN J. PRITCHARD,2
AND
FOR
MATTHEW J. BARNES1
1
School of Sport and Exercise, Massey University, Palmerston North, New Zealand; and 2Department of Exercise & Sport Science, Universal College of Learning, Palmerston North, New Zealand ABSTRACT
Cochrane, DJ, Coley, KW, Pritchard, HJ, and Barnes, MJ. Vibration exercise as a warm-up modality for deadlift power output. J Strength Cond Res 29(4): 1033–1039, 2015—Vibration exercise (VbX) has gained popularity as a warm-up modality to enhance performance in golf, baseball, and sprint cycling, but little is known about the efficacy of using VbX as a warm-up before resistance exercise, such as deadlifting. The aim of this study was to compare the effects of a deadlift (DL)-specific warm-up, VbX warm-up, and Control on DL power output (PO). The DL warm-up (DL-WU) included 10, 8, and 5 repetitions performed at 30, 40, and 50% 1-repetition maximum (1RM), respectively, where the number of repetitions was matched by body-weight squats performed with vibration and without vibration (Control). The warm-up conditions were randomized and performed at least 2 days apart. Peak power (PP), mean power, rate of force development (RFD), and electromyography (EMG) were measured during the concentric phase of 2 consecutive DLs (75% 1RM) at 30 seconds and 2:30 minutes after the warm-up conditions. There was no significant (p . 0.05) main effect or interaction effect between the DL-WU, VbX warm-up, and Control for PP, mean power, RFD, and EMG. Vibration exercise warm-up did not exhibit an ergogenic effect to potentiate muscle activity more than the specific DLWU and Control. Therefore, DL PO is affected to a similar extent, irrespective of the type of stimuli, when the warm-up is not focused on raising muscle temperature.
KEY WORDS resistance training, postactivation potentiation, electromyography, peak power, rate of force development INTRODUCTION
T
he deadlift (DL) is a popular compound exercise used to develop strength and power in the muscles of the lower body and, additionally, it is 1 of 3 lifts performed in the sport of powerlifting, along with
Address correspondence to Darryl J. Cochrane, [email protected]. 29(4)/1033–1039 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
the squat and bench press. Although other movements, such as the Olympic lifts and their variations, are traditionally viewed as producing higher power outputs (POs) than the lower body powerlifts (DL and squat) (22,23), Swinton et al. (39) suggest that the DL is appropriate for use in a periodized program aimed at developing muscular power. Recommendations for power training suggest that multijoint exercises, such as the DL, be performed at the start of a training session (3), which minimizes fatigue and maximizes power and force output during the movement. To ensure optimal performance, and reduce the chance of injury, an appropriate warm-up is important before performing such a physiologically stressful exercise (43). In training and before competition, a DL warm-up (DLWU) routine typically involves completing submaximal strength loads subsequent to the main workout or competition lift; anecdotally, this often occurs in the absence of a prior aerobic activity. The DL-WU, therefore, has an important role in preparing the athlete for optimal force and power production to maximize lifting performance. The benefits of warming up before short-duration activities, such as resistance exercise, have been well documented and may be because of temperature and non–temperature dependent factors (for a full review, see Bishop [8]). Various warm-up methods, including active and passive modalities, are traditionally used; however, new and more time efficient warm-up modalities are often sought to further enhance performance. A modality that is time efficient and that requires little metabolic demand, while enhancing performance, would be advantageous for warming up, especially when preservation of energy is the main priority before exercise. One plausible option that meets these requirements is vibration exercise (VbX), which has gained popularity as a warm-up modality because of its time efficiency for enhancing non–temperature related effects of muscle activation properties (18), blood flow (28), and mild metabolic changes (16), while accelerating temperature-related effects of muscle temperature at a greater rate than passive and active warm-ups (19). Additionally, the use of VbX as a warm-up has been shown to enhance performance in golf (12), baseball (35), and sprint cycling (5). Vibration exercise is primarily performed on a vertically oscillating platform VOLUME 29 | NUMBER 4 | APRIL 2015 |
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Vibration and Deadlift Warm-Up where energy is transferred from the vibrating platform to the body. The acceleration of the body, vertically, is dampened by the muscles of the lower limbs so that energy, from VbX, is absorbed and heat is subsequently generated (42). Additionally, VbX-related changes in muscle fiber length elicit reflexive muscle contractions (33,36), which in turn increases muscle activity (2,36) and enhances cortical motor excitability (29). Acute VbX studies have also reported increases in muscular power (10,19) and force (26,38); however, it is unclear whether VbX alters DL performance. A sport-specific warm-up has the ability to enhance neuromuscular activation and performance (8), but it is unclear whether VbX can augment PO more than a specific DL-WU can. Therefore, this study focused on comparing the performance effects of a DL-specific warm-up with a VbX warm-up and body-weight control. Additionally, the neuromuscular contribution of each warm-up modality to performance was investigated by using surface electromyography (EMG). Based on previous research that VbX elicits an ergogenic effect (17,19), we hypothesized that a VbX warm-up would increase muscle activity (EMG) and enhance DL PO to a greater extent than either an incrementally loaded, specific DL-WU or Control movement.
METHODS
order was allocated in a randomized, counterbalanced design. Each trial was separated by 2–5 days, depending on subject availability. To account for daily biorhythms, all conditions were conducted at the same time of the day. The participants were encouraged to maintain their dietary, sleeping, drinking habits, and instructed to refrain from physical and power training at least 24 hours before testing. Subjects
Twelve healthy men (age 25.9 6 7.2 years; height 1.78 6 0.1 m; body mass 86.3 6 16.7 kg) with at least 3 years of recreational resistance training and DL experience (6.0 6 2.7 years) and 1 repetition maximum (1RM) DL of 185 6 66.5 kg (2.1 6 0.5 1RM$kg21 body weight) volunteered for the study. Written informed consent was obtained from the participants, and ethical approval was granted by the University Human Ethics Committee. One-Repetition Maximum Deadlift
Before 1RM testing, the participants performed a warm-up by completing 3 sets of DL; 10 repetitions at 30%, 8 repetitions at 40%, and 5 repetitions at 50% of the estimated 1RM. A standard Olympic bar and plate weights were used during the study. The 1RM DL was achieved by increasing the load so that 1RM was reached in 3–5 attempts (11); each attempt was separated by 4 minutes of rest.
Experimental Approach to the Problem
The design of the study was to test the efficacy of implementing VbX as a warm-up before deadlifting and compare it with a DL-specific warm-up and Control condition. Taking into consideration that all lifters have their own warm-up routine before training and competition, a DL-WU was developed to include repetitions and weight loading (% RM) that characterized a common DL training warm-up; this is often performed without an aerobic component in both training and competition. The DL-WU included 10, 8, and 5 repetitions performed at 30, 40, and 50% 1RM, respectively, where the number of repetitions was matched by body-weight squats performed on a vibration plate (VbX warm-up) and the Control that included the dynamic squatting technique without vibration. Peak power (PP), mean power, and rate of force development (RFD) were measured during the concentric phase of 2 consecutive DLs at 30 seconds and 2:30 minutes after 3 warm-up conditions. The time intervals were selected from previous research where VbX is capable of increasing performance for up to 5 minutes (4,18). Additionally, EMG was analyzed to elucidate possible mechanisms that may affect DL performance. Before undertaking the trials, 1RM DL was measured, and the participants were familiarized with the vibration platform. Within 2 days of RM testing, the participants performed 3 warm-up conditions on separate days: (a) VbX with dynamic squatting (VbX-WU), (b) DL-WU, and (c) dynamic squatting without VbX (Control). The condition
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Warm-Up Conditions
Deadlift Warm-Up. The participants performed 3 sets of conventional DL for 10 repetitions (30% 1RM), 8 repetitions (40% 1RM), and 5 repetitions (50% 1RM) with 60 seconds of rest separating each set. Each repetition was performed in a controlled manner at a tempo of approximately 1–2 seconds up and 1–2 seconds down. VbX With Dynamic Squatting. A commercial machine with a motorized side-alternating platform produced vertical sinusoidal vibrations (Galileo Sport; Novotec, Pforzheim, Germany). The participants wore the same sport shoes for all warm-up conditions and were instructed to place each foot 18 cm from the central axis and distribute their weight through the soles of their feet. They proceeded to squat up and down at a tempo of 1–2 seconds down and 1–2 seconds up to an approximate depth of 908 knee flexion. As with the DL-WU, the participants completed sets of 10, 8, and 5 repetitions separated by 60 seconds of rest between sets, thereby matching repetition number and exercise time. A single axis accelerometer (Imems, ADXL250; Analog Devices, Norwood, MA, USA) was secured to the edge of the vibrating platform, and it recorded an acceleration of 91.0 6 0.02 m$s22 at 26 Hz (6.4 mm, peak-to-peak displacement [p-p]). The frequency of 26 Hz was selected based on previous side-alternating VbX research that has reported to increase muscle temperature (19), and enhance neuromuscular aspects such as muscle activity and stretch reflex (15).
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TABLE 1. Duration to complete the various warm-up repetitions for VbX-WU, DL-WU, and control.* Condition Repetitions (s)
VbX-WU†
DL-WU
Controlz
10§k 8¶ 5
38.0 6 3.4 32.0 6 3.0 20.5 6 3.5
35.7 6 6.5 26.9 6 5.3 18.2 6 3.2
32.1 6 7.1 26.4 6 4.7 16.5 6 2.8
*VbX-WU = VbX with dynamic squatting; DL-WU = deadlift warm-up. †VbX-WU compared with DL-WU (p # 0.05). zControl compared with VbX-WU (p , 0.001). §Ten repetitions compared with 8 repetitions (p , 0.001). kTen repetitions compared with 5 repetitions (p , 0.001). ¶Eight repetitions compared with 5 repetitions (p , 0.001).
Control. For the Control condition, the vibration machine was switched off, and the participants performed the exact dynamic squatting technique as VbX-WU. Performance Measures
The participants performed 2 consecutive DL repetitions (75% 1RM) at 30 seconds and 2:30 minutes postcondition, for which they were required to lift the load as quickly and as explosively as possible. Peak power, mean concentric power (MCP), and RFD of the concentric phase were measured from a linear position transducer (GymAware Power Tool 5; Kinetic Performance Technology, Canberra, Australia), which has been shown to be a valid and reliable device for measuring power and force indices (21). Bar displacement was measured by placing the transducer on the floor and attaching the retractable tether to the middle of the Olympic bar. Instantaneous velocity and acceleration were calculated from first- and second-order derivatives, and force was calculated from the product of acceleration and mass of the bar. Power output was determined every 3 mm of bar movement by the product of force and velocity, and MCP was averaged over the concentric phase of the lift. Rate of force development was calculated from the steepest slope of the force curve within the concentric
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phase. The transducer sampled at 50 Hz, and data were collected and stored via Bluetooth on an iPod (model A1367; Apple, CA, USA). The highest values of PP, MCP, and RFD from the 2 DL repetitions were expressed relative to body weight (per kilogram) and used for subsequent analysis. Electromyography
Muscle activity of the right vastus lateralis (VL), biceps femoris (BF), and gluteus maximus (GM) muscles was measured using surface EMG. Before electrode placement, the area was shaved, gently abraded, and cleaned with isopropyl alcohol. Surface pregelled Ag–AgCl electrodes, 10-mm diameter (Medicostest, Rugmarken, Denmark), were placed at an interelectrode distance of 20 mm over the midbelly of the muscle parallel to the direction of the fibers according to surface EMG for the Noninvasive Assessment of Muscles recommendations (24). To ensure identical placement for subsequent trials, the site of each electrode was outlined with a permanent marker. The electrodes were connected to wireless EMG sensors that were securely fastened to the measurement site with adhesive tape. The sensors preamplified the EMG signals using a first-order high pass filter (10 Hz) at a gain of 400. The EMG signals were then transmitted telemetrically in real time to a personal computer interface receiver (Telemyo DTS; Noraxon, Scottsdale, AZ, USA) and were recorded by a data acquisition system (MyoResearch XP Master; Noraxon, Scottsdale, AZ, USA). Data were filtered with a low pass filter of 500 Hz and sampled at 3,000 Hz, which was synchronized with video capture (HD Webcam C615; Logitech, Hong Kong, China). Subsequently, the raw EMG data were rectified and smoothed over 100 milliseconds (root means square algorithm). The EMGrms mean
TABLE 2. Peak power, MCP, and RFD after VbX-WU, DL-WU, and control.* VbX-WU
PP (W$kg21) MCP (W$kg21) RFD (kN$s21)
DL-WU
Control
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
15.3 6 1.8 8.2 6 1.2 0.10 6 0.13
15.9 6 2.5 8.5 6 1.0 0.11 6 0.11
14.8 6 2.2 8.2 6 1.5 0.17 6 0.13
15.2 6 2.7 8.3 6 1.6 0.14 6 0.14
14.9 6 2.4 8.2 6 1.2 0.14 6 0.12
15.2 6 2.9 8.2 6 1.5 0.11 6 0.12
*PP = peak power; MCP = mean concentric power; RFD = rate of force development; VbX-WU = VbX with dynamic squatting; DL-WU = deadlift warm-up.
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Vibration and Deadlift Warm-Up
TABLE 3. EMGrms mean amplitude of VL, BF, GM after VbX-WU, DL-WU, and control.* VbX-WU
VL (mV) BF (mV) GM (mV)
DL-WU
Control
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
285.2 6 110.6 265.0 6 117.8 214.8 6 155.8
281.0 6 96.6 278.0 6 85.2 230.2 6 171.3
257.7 6 88.7 272.4 6 98.8 241.4 6 159.8
256.2 6 98.0 273.3 6 98.2 252.2 6 198.2
282.0 6 102.2 271.2 6 120.1 209.5 6 148.6
293.0 6 112.4 267.9 6 101.4 190.5 6 128.3
*VL = vastus lateralis; BF = biceps femoris; GM = gluteus maximus; VbX-WU = VbX with dynamic squatting; DL-WU = deadlift warm-up.
amplitude of VL, BF, and GM was analyzed for each condition (VbX-WU, DL-WU, and Control) and for the time interval (post-30 seconds, post-2:30 minutes) during the concentric phase of the DL (from the initial bar movement to attaining an upright position). Statistical Analyses
The muscular performance measures (PP, MCP, and RFD) and EMGrms of VL, BF, and GM from the 3 warm-up conditions and time intervals were evaluated using repeated measure analysis of variance using SPSS for Windows (version 20.0; IBM, New York, NY, USA). When a significant F-value was achieved, post hoc comparisons were performed using the Bonferroni procedure, and the level of significance was fixed at p # 0.05. To determine test-retest reliability of the PP, the intraclass correlation coefficient revealed was 0.903 with a coefficient correlation of 15.1%.
RESULTS The duration to complete the various warm-up conditions (Table 1) resulted in a main effect that VbX-WU took an additional 3.2 and 5.2 seconds compared with DL-WU (p , 0.001) and Control (p # 0.05), respectively. Likewise, the greater the number of repetitions performed, the longer these took to complete (p , 0.001), but there was no interaction effect (p = 0.246). There was no significant (p . 0.05) main effect or interaction effect among VbX-WU, DL-WU, and Control for PP, MCP, and RFD (Table 2). Similarly, there was no significant (p . 0.05) change in the EMGrms of VL, BF, and GM among the 3 conditions (Table 3).
DISCUSSION The hypothesis that VbX-WU (dynamic squatting with vibration) can increase muscle activity and enhance DL performance more than a specific DL-WU and bodyweight squatting (Control) can was not confirmed. However, in other sports, such as golf, VbX warm-up has been shown to significantly enhance golf swing by increasing longer drive distances (12) and augments PP in sprint
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cycling (5). Similarly, VbX warm-up can enhance bat speed in baseball when vibration is combined with lower and upper-limb exercises (35). The discrepancy between the results of this study and of the aforementioned literature may be attributed to methodological differences and the type of performance being investigated. In this study, we attempted to match the number of repetitions and sets for all 3 warm-up conditions; although, VbX-WU took longer to complete compared with DL-WU and Control, the total duration of the vibration exposure was only 90.5 seconds, which may have been insufficient to elicit the required neuromuscular responses. In comparison, other successful sporting VbX warm-ups have implemented longer intermittent vibration exposures that have totaled 4 minutes (12) and 7 minutes (35). Muscle force and power have been reported to be potentiated after acute VbX, where the effects of VbX are postulated to be synonymous with conventional resistance and explosive power training (9,13). This claim is based on the assumption that neural factors, similar to those neural changes seen in the initial stages of traditional resistance and power training, are responsible for the increases in force and power. Vibration exercise is capable of increasing muscle activity (2,36), where the excitatory responses of the muscle spindle may play a role in enhancing muscle activation (34,36). Therefore, we speculated that VbX warm-up would greatly enhance neuromuscular activity and augment DL PO more than a DL-specific warm-up and Control would. However, the EMG activity revealed no difference between the 3 warm-up conditions, suggesting that the magnitude of VbX and loading intensity of DL may have been insufficient to influence neural factors beyond that of body-weight squats (Control) to enhancing DL performance. The literature recommends that, to elicit postactivation potentiation (PAP), resistance exercises should be performed with maximal or near maximal loading (25); however, the loading regime remains equivocal because of inconsistent findings of increased or no change in performance (40). Although no measures of PAP were taken during this study, it is plausible that PAP could account for the current
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Journal of Strength and Conditioning Research findings. Postactivation potentiation has been documented after VbX (18,31), submaximal loads (14,37), heavy loads (3–5RM) (27,30), and recent research has shown that using low-intensity body-weighted exercises significantly improved explosive power compared with using VbX-WU and no warm-up (20). The proposed mechanism of PAP includes motor unit excitability, phosphorylation of myosin regulatory light chains, and pennation angle (40). Alternatively, the warm-up conditions may have lacked the necessary stimulus to elicit PAP; the lack of a pre–warm-up performance measure because of safety considerations means that it is unclear whether any of these protocols elicited PAP. The current warm-up conditions were influenced by various practical considerations: it is not feasible to perform maximal or near maximal efforts because this could induce fatigue and affect our main outcome measures related to lifting performance; to replicate training and competition, it is common practice for lifters to use a DL-specific warm-up regime only; therefore, we deliberately did not include an aerobic component in the current warm-ups. However, excluding the aerobic component may have conserved valuable energy, but it may have caused a detrimental effect where temperature-related warm-up factors, such as muscle temperature and nerve conduction velocity, had little chance of being elevated. According to Bishop (8), short-duration performance enhancement is largely attributable to muscle temperature, and the availability of high-energy phosphates such that the warm-up needs to be of sufficient intensity and duration to maximize the increase in muscle temperature, in the absence of fatigue. It was beyond the scope of the study to measure temperature-related mechanisms, but the exclusion of the aerobic component and the brevity in duration of the current protocols may explain why all 3 warm-up conditions had similar findings. This was probably because of the inability to raise muscle temperature to an adequate level, and thus prevents an increase in subsequent DL performance. Previous work has indicated that 5 minutes of continuous VbX (26 Hz, 6 mmp-p) increased muscle temperature by 1.58 C and enhanced vertical jump performance by 8% (19). The recommendations of the American College of Sports Medicine (3), National Strength and Conditioning Association (6), and American Society of Exercise Physiologists (ASEP) (11) indicate that a general warm-up (5– 10 minutes, 40% V_ O2max) should precede a specific warm-up before undertaking maximum strength testing (1). Recently, it has been reported that a general warmup using cycle ergometry performed at a longer duration (15 minutes) and low intensity (40% V_ O2max) significantly improved 1RM leg press compared with the recommended duration of 5–10 minutes at low intensity (7). However, it may not be practically feasible to implement an aerobic component, especially when time is limited or repeated lifts are required over extended periods, such as in strength- and
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power-based events. In these instances, maintenance of muscle temperature at a reasonable level, while minimizing energy cost, may offer the best solution for performance enhancement. There is a possibility that psychological preparation (psyching up) before lifting the submaximal DL load (75% 1RM) may have activated higher motor centers thus overriding any warm-up effect that the 3 conditions may have had. Although the effects of “psyching up” before maximal effort resistance exercise are equivocal (41), there have been anecdotal reports where moderateheavy loads have been lifted successfully with minimal or no warm-up indicating that higher commands may be responsible for completing such efforts. Further, it is important to note that the current DL-WU protocol had a higher volume compared with the recommended warm-up guideline for 1RM testing (11). Nevertheless, because lifters have their own warm-up routine, which may vary in sets, repetitions, and loading, further research is warranted to investigate whether a range of DL-WU loads (heavier) and different VbX parameters can further influence DL performance. The optimal load for maximizing PO during the DL is not well known, particularly across a range of athletes with different training backgrounds and strength levels. In highly trained powerlifters, DL PP has been shown to occur at a load equivalent to 30% 1RM (39). With this load, Swinton et al. (39) reported PP in excess of 4,300 W, while at a similar load (70% 1RM) to that used in this study, they reported PO approximately twice the PP of this study. Given the lack of consensus for PP in the DL, and other movements, across populations, a “bandwidth” of loads that maximizes PO has been suggested (19); the load used in this study was at the upper end of this suggested “bandwidth.” Clearly, further investigation of PO in the DL is warranted. In conclusion, previous research has indicated that VbX warm-up can enhance sporting performance (5,12,32,35), but the results of this study indicate that for short-term activities, such as deadlifting, VbX-WU produces a muscular performance similar to that of a specific DL-WU and bodyweight squatting (Control). This further suggests that increasing muscle temperature, via aerobic exercise, is probably the most important factor to enhancing subsequent short-term performance (8), unless an appropriate load can guarantee a PAP response.
PRACTICAL APPLICATIONS The current findings suggest that, in the absence of an aerobic warm-up component, body-weight squats, with or without VbX, bring about similar PP outputs as those occurring after a DL-specific warm-up. Therefore, when the training load is submaximal in nature and the intention is to develop high POs, the incorporation of movements specific to the planned lift, irrespective of external load or stimulus, should be encouraged during the warm-up. VOLUME 29 | NUMBER 4 | APRIL 2015 |
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Vibration and Deadlift Warm-Up Warming up before training and competition is often determined by the practicalities and requirements of the sport; the results of this study support the continued use of a progressive DL-specific warm-up to assist the athlete in reaching an appropriate level of preparedness, even if it may come with an additional physiological cost.
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34. Pollock, RD, Woledge, RC, Martin, FC, and Newham, DJ. Effects of whole body vibration on motor unit recruitment and threshold. J Appl Physiol 112: 388–395, 2012. 35. Reyes, GFC, Dickin, DC, Dolny, DG, and Crusat, NJK. Effects of muscular strength, exercise order, and acute whole-body vibration exposure on bat swing speed. J Strength Cond Res 24: 3234–3240, 2010. 36. Ritzmann, R, Kramer, A, Gruber, M, Gollhofer, A, and Taube, W. EMG activity during whole body vibration: Motion artifacts or stretch reflexes? Eur J Appl Physiol 110: 143–151, 2010.
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Journal of Strength and Conditioning Research 37. Sotiropoulos, K, Smilios, I, Christou, M, Barzouka, K, Spaias, A, Douda, H, and Tokmakidis, SP. Effects of warm-up on vertical jump performance and muscle electrical activity using half-squats at low and moderate intensity. J Sports Sci Med 9: 326–331, 2010. 38. Stewart, JA, Cochrane, DJ, and Morton, RH. Differential effects of whole body vibration durations on knee extensor strength. J Sci Med Sport 12: 50–53, 2009. 39. Swinton, PA, Stewart, A, Agouris, I, Keogh, JWL, and Lloyd, R. A biomechanical analysis of straight and hexagonal barbell deadlifts using submaximal loads. J Strength Cond Res 25: 2000– 2009, 2011.
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40. Tillin, NA and Bishop, D. Factors modulating post-activation potentiation and its effect on performance of subsequent explosive activities. Sports Med 39: 147–166, 2009. 41. Tod, D, Iredale, F, and Gill, N. “Psyching-up” and muscular force production. Sports Med 33: 47–58, 2003. 42. Wakeling, JM, Nigg, BM, and Rozitis, AI. Muscle activity damps the soft tissue resonance that occurs in response to pulsed and continuous vibrations. J Appl Physiol 93: 1093–1103, 2002. 43. Woods, K, Bishop, P, and Jones, E. Warm-up and stretching in the prevention of muscular injury. Sports Med 37: 1089–1099, 2007.
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AND
FOR
MATTHEW J. BARNES1
1
School of Sport and Exercise, Massey University, Palmerston North, New Zealand; and 2Department of Exercise & Sport Science, Universal College of Learning, Palmerston North, New Zealand ABSTRACT
Cochrane, DJ, Coley, KW, Pritchard, HJ, and Barnes, MJ. Vibration exercise as a warm-up modality for deadlift power output. J Strength Cond Res 29(4): 1033–1039, 2015—Vibration exercise (VbX) has gained popularity as a warm-up modality to enhance performance in golf, baseball, and sprint cycling, but little is known about the efficacy of using VbX as a warm-up before resistance exercise, such as deadlifting. The aim of this study was to compare the effects of a deadlift (DL)-specific warm-up, VbX warm-up, and Control on DL power output (PO). The DL warm-up (DL-WU) included 10, 8, and 5 repetitions performed at 30, 40, and 50% 1-repetition maximum (1RM), respectively, where the number of repetitions was matched by body-weight squats performed with vibration and without vibration (Control). The warm-up conditions were randomized and performed at least 2 days apart. Peak power (PP), mean power, rate of force development (RFD), and electromyography (EMG) were measured during the concentric phase of 2 consecutive DLs (75% 1RM) at 30 seconds and 2:30 minutes after the warm-up conditions. There was no significant (p . 0.05) main effect or interaction effect between the DL-WU, VbX warm-up, and Control for PP, mean power, RFD, and EMG. Vibration exercise warm-up did not exhibit an ergogenic effect to potentiate muscle activity more than the specific DLWU and Control. Therefore, DL PO is affected to a similar extent, irrespective of the type of stimuli, when the warm-up is not focused on raising muscle temperature.
KEY WORDS resistance training, postactivation potentiation, electromyography, peak power, rate of force development INTRODUCTION
T
he deadlift (DL) is a popular compound exercise used to develop strength and power in the muscles of the lower body and, additionally, it is 1 of 3 lifts performed in the sport of powerlifting, along with
Address correspondence to Darryl J. Cochrane, [email protected]. 29(4)/1033–1039 Journal of Strength and Conditioning Research Ó 2015 National Strength and Conditioning Association
the squat and bench press. Although other movements, such as the Olympic lifts and their variations, are traditionally viewed as producing higher power outputs (POs) than the lower body powerlifts (DL and squat) (22,23), Swinton et al. (39) suggest that the DL is appropriate for use in a periodized program aimed at developing muscular power. Recommendations for power training suggest that multijoint exercises, such as the DL, be performed at the start of a training session (3), which minimizes fatigue and maximizes power and force output during the movement. To ensure optimal performance, and reduce the chance of injury, an appropriate warm-up is important before performing such a physiologically stressful exercise (43). In training and before competition, a DL warm-up (DLWU) routine typically involves completing submaximal strength loads subsequent to the main workout or competition lift; anecdotally, this often occurs in the absence of a prior aerobic activity. The DL-WU, therefore, has an important role in preparing the athlete for optimal force and power production to maximize lifting performance. The benefits of warming up before short-duration activities, such as resistance exercise, have been well documented and may be because of temperature and non–temperature dependent factors (for a full review, see Bishop [8]). Various warm-up methods, including active and passive modalities, are traditionally used; however, new and more time efficient warm-up modalities are often sought to further enhance performance. A modality that is time efficient and that requires little metabolic demand, while enhancing performance, would be advantageous for warming up, especially when preservation of energy is the main priority before exercise. One plausible option that meets these requirements is vibration exercise (VbX), which has gained popularity as a warm-up modality because of its time efficiency for enhancing non–temperature related effects of muscle activation properties (18), blood flow (28), and mild metabolic changes (16), while accelerating temperature-related effects of muscle temperature at a greater rate than passive and active warm-ups (19). Additionally, the use of VbX as a warm-up has been shown to enhance performance in golf (12), baseball (35), and sprint cycling (5). Vibration exercise is primarily performed on a vertically oscillating platform VOLUME 29 | NUMBER 4 | APRIL 2015 |
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Vibration and Deadlift Warm-Up where energy is transferred from the vibrating platform to the body. The acceleration of the body, vertically, is dampened by the muscles of the lower limbs so that energy, from VbX, is absorbed and heat is subsequently generated (42). Additionally, VbX-related changes in muscle fiber length elicit reflexive muscle contractions (33,36), which in turn increases muscle activity (2,36) and enhances cortical motor excitability (29). Acute VbX studies have also reported increases in muscular power (10,19) and force (26,38); however, it is unclear whether VbX alters DL performance. A sport-specific warm-up has the ability to enhance neuromuscular activation and performance (8), but it is unclear whether VbX can augment PO more than a specific DL-WU can. Therefore, this study focused on comparing the performance effects of a DL-specific warm-up with a VbX warm-up and body-weight control. Additionally, the neuromuscular contribution of each warm-up modality to performance was investigated by using surface electromyography (EMG). Based on previous research that VbX elicits an ergogenic effect (17,19), we hypothesized that a VbX warm-up would increase muscle activity (EMG) and enhance DL PO to a greater extent than either an incrementally loaded, specific DL-WU or Control movement.
METHODS
order was allocated in a randomized, counterbalanced design. Each trial was separated by 2–5 days, depending on subject availability. To account for daily biorhythms, all conditions were conducted at the same time of the day. The participants were encouraged to maintain their dietary, sleeping, drinking habits, and instructed to refrain from physical and power training at least 24 hours before testing. Subjects
Twelve healthy men (age 25.9 6 7.2 years; height 1.78 6 0.1 m; body mass 86.3 6 16.7 kg) with at least 3 years of recreational resistance training and DL experience (6.0 6 2.7 years) and 1 repetition maximum (1RM) DL of 185 6 66.5 kg (2.1 6 0.5 1RM$kg21 body weight) volunteered for the study. Written informed consent was obtained from the participants, and ethical approval was granted by the University Human Ethics Committee. One-Repetition Maximum Deadlift
Before 1RM testing, the participants performed a warm-up by completing 3 sets of DL; 10 repetitions at 30%, 8 repetitions at 40%, and 5 repetitions at 50% of the estimated 1RM. A standard Olympic bar and plate weights were used during the study. The 1RM DL was achieved by increasing the load so that 1RM was reached in 3–5 attempts (11); each attempt was separated by 4 minutes of rest.
Experimental Approach to the Problem
The design of the study was to test the efficacy of implementing VbX as a warm-up before deadlifting and compare it with a DL-specific warm-up and Control condition. Taking into consideration that all lifters have their own warm-up routine before training and competition, a DL-WU was developed to include repetitions and weight loading (% RM) that characterized a common DL training warm-up; this is often performed without an aerobic component in both training and competition. The DL-WU included 10, 8, and 5 repetitions performed at 30, 40, and 50% 1RM, respectively, where the number of repetitions was matched by body-weight squats performed on a vibration plate (VbX warm-up) and the Control that included the dynamic squatting technique without vibration. Peak power (PP), mean power, and rate of force development (RFD) were measured during the concentric phase of 2 consecutive DLs at 30 seconds and 2:30 minutes after 3 warm-up conditions. The time intervals were selected from previous research where VbX is capable of increasing performance for up to 5 minutes (4,18). Additionally, EMG was analyzed to elucidate possible mechanisms that may affect DL performance. Before undertaking the trials, 1RM DL was measured, and the participants were familiarized with the vibration platform. Within 2 days of RM testing, the participants performed 3 warm-up conditions on separate days: (a) VbX with dynamic squatting (VbX-WU), (b) DL-WU, and (c) dynamic squatting without VbX (Control). The condition
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Warm-Up Conditions
Deadlift Warm-Up. The participants performed 3 sets of conventional DL for 10 repetitions (30% 1RM), 8 repetitions (40% 1RM), and 5 repetitions (50% 1RM) with 60 seconds of rest separating each set. Each repetition was performed in a controlled manner at a tempo of approximately 1–2 seconds up and 1–2 seconds down. VbX With Dynamic Squatting. A commercial machine with a motorized side-alternating platform produced vertical sinusoidal vibrations (Galileo Sport; Novotec, Pforzheim, Germany). The participants wore the same sport shoes for all warm-up conditions and were instructed to place each foot 18 cm from the central axis and distribute their weight through the soles of their feet. They proceeded to squat up and down at a tempo of 1–2 seconds down and 1–2 seconds up to an approximate depth of 908 knee flexion. As with the DL-WU, the participants completed sets of 10, 8, and 5 repetitions separated by 60 seconds of rest between sets, thereby matching repetition number and exercise time. A single axis accelerometer (Imems, ADXL250; Analog Devices, Norwood, MA, USA) was secured to the edge of the vibrating platform, and it recorded an acceleration of 91.0 6 0.02 m$s22 at 26 Hz (6.4 mm, peak-to-peak displacement [p-p]). The frequency of 26 Hz was selected based on previous side-alternating VbX research that has reported to increase muscle temperature (19), and enhance neuromuscular aspects such as muscle activity and stretch reflex (15).
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TABLE 1. Duration to complete the various warm-up repetitions for VbX-WU, DL-WU, and control.* Condition Repetitions (s)
VbX-WU†
DL-WU
Controlz
10§k 8¶ 5
38.0 6 3.4 32.0 6 3.0 20.5 6 3.5
35.7 6 6.5 26.9 6 5.3 18.2 6 3.2
32.1 6 7.1 26.4 6 4.7 16.5 6 2.8
*VbX-WU = VbX with dynamic squatting; DL-WU = deadlift warm-up. †VbX-WU compared with DL-WU (p # 0.05). zControl compared with VbX-WU (p , 0.001). §Ten repetitions compared with 8 repetitions (p , 0.001). kTen repetitions compared with 5 repetitions (p , 0.001). ¶Eight repetitions compared with 5 repetitions (p , 0.001).
Control. For the Control condition, the vibration machine was switched off, and the participants performed the exact dynamic squatting technique as VbX-WU. Performance Measures
The participants performed 2 consecutive DL repetitions (75% 1RM) at 30 seconds and 2:30 minutes postcondition, for which they were required to lift the load as quickly and as explosively as possible. Peak power, mean concentric power (MCP), and RFD of the concentric phase were measured from a linear position transducer (GymAware Power Tool 5; Kinetic Performance Technology, Canberra, Australia), which has been shown to be a valid and reliable device for measuring power and force indices (21). Bar displacement was measured by placing the transducer on the floor and attaching the retractable tether to the middle of the Olympic bar. Instantaneous velocity and acceleration were calculated from first- and second-order derivatives, and force was calculated from the product of acceleration and mass of the bar. Power output was determined every 3 mm of bar movement by the product of force and velocity, and MCP was averaged over the concentric phase of the lift. Rate of force development was calculated from the steepest slope of the force curve within the concentric
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phase. The transducer sampled at 50 Hz, and data were collected and stored via Bluetooth on an iPod (model A1367; Apple, CA, USA). The highest values of PP, MCP, and RFD from the 2 DL repetitions were expressed relative to body weight (per kilogram) and used for subsequent analysis. Electromyography
Muscle activity of the right vastus lateralis (VL), biceps femoris (BF), and gluteus maximus (GM) muscles was measured using surface EMG. Before electrode placement, the area was shaved, gently abraded, and cleaned with isopropyl alcohol. Surface pregelled Ag–AgCl electrodes, 10-mm diameter (Medicostest, Rugmarken, Denmark), were placed at an interelectrode distance of 20 mm over the midbelly of the muscle parallel to the direction of the fibers according to surface EMG for the Noninvasive Assessment of Muscles recommendations (24). To ensure identical placement for subsequent trials, the site of each electrode was outlined with a permanent marker. The electrodes were connected to wireless EMG sensors that were securely fastened to the measurement site with adhesive tape. The sensors preamplified the EMG signals using a first-order high pass filter (10 Hz) at a gain of 400. The EMG signals were then transmitted telemetrically in real time to a personal computer interface receiver (Telemyo DTS; Noraxon, Scottsdale, AZ, USA) and were recorded by a data acquisition system (MyoResearch XP Master; Noraxon, Scottsdale, AZ, USA). Data were filtered with a low pass filter of 500 Hz and sampled at 3,000 Hz, which was synchronized with video capture (HD Webcam C615; Logitech, Hong Kong, China). Subsequently, the raw EMG data were rectified and smoothed over 100 milliseconds (root means square algorithm). The EMGrms mean
TABLE 2. Peak power, MCP, and RFD after VbX-WU, DL-WU, and control.* VbX-WU
PP (W$kg21) MCP (W$kg21) RFD (kN$s21)
DL-WU
Control
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
15.3 6 1.8 8.2 6 1.2 0.10 6 0.13
15.9 6 2.5 8.5 6 1.0 0.11 6 0.11
14.8 6 2.2 8.2 6 1.5 0.17 6 0.13
15.2 6 2.7 8.3 6 1.6 0.14 6 0.14
14.9 6 2.4 8.2 6 1.2 0.14 6 0.12
15.2 6 2.9 8.2 6 1.5 0.11 6 0.12
*PP = peak power; MCP = mean concentric power; RFD = rate of force development; VbX-WU = VbX with dynamic squatting; DL-WU = deadlift warm-up.
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Vibration and Deadlift Warm-Up
TABLE 3. EMGrms mean amplitude of VL, BF, GM after VbX-WU, DL-WU, and control.* VbX-WU
VL (mV) BF (mV) GM (mV)
DL-WU
Control
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
Post-30 s
Post-2:30 min
285.2 6 110.6 265.0 6 117.8 214.8 6 155.8
281.0 6 96.6 278.0 6 85.2 230.2 6 171.3
257.7 6 88.7 272.4 6 98.8 241.4 6 159.8
256.2 6 98.0 273.3 6 98.2 252.2 6 198.2
282.0 6 102.2 271.2 6 120.1 209.5 6 148.6
293.0 6 112.4 267.9 6 101.4 190.5 6 128.3
*VL = vastus lateralis; BF = biceps femoris; GM = gluteus maximus; VbX-WU = VbX with dynamic squatting; DL-WU = deadlift warm-up.
amplitude of VL, BF, and GM was analyzed for each condition (VbX-WU, DL-WU, and Control) and for the time interval (post-30 seconds, post-2:30 minutes) during the concentric phase of the DL (from the initial bar movement to attaining an upright position). Statistical Analyses
The muscular performance measures (PP, MCP, and RFD) and EMGrms of VL, BF, and GM from the 3 warm-up conditions and time intervals were evaluated using repeated measure analysis of variance using SPSS for Windows (version 20.0; IBM, New York, NY, USA). When a significant F-value was achieved, post hoc comparisons were performed using the Bonferroni procedure, and the level of significance was fixed at p # 0.05. To determine test-retest reliability of the PP, the intraclass correlation coefficient revealed was 0.903 with a coefficient correlation of 15.1%.
RESULTS The duration to complete the various warm-up conditions (Table 1) resulted in a main effect that VbX-WU took an additional 3.2 and 5.2 seconds compared with DL-WU (p , 0.001) and Control (p # 0.05), respectively. Likewise, the greater the number of repetitions performed, the longer these took to complete (p , 0.001), but there was no interaction effect (p = 0.246). There was no significant (p . 0.05) main effect or interaction effect among VbX-WU, DL-WU, and Control for PP, MCP, and RFD (Table 2). Similarly, there was no significant (p . 0.05) change in the EMGrms of VL, BF, and GM among the 3 conditions (Table 3).
DISCUSSION The hypothesis that VbX-WU (dynamic squatting with vibration) can increase muscle activity and enhance DL performance more than a specific DL-WU and bodyweight squatting (Control) can was not confirmed. However, in other sports, such as golf, VbX warm-up has been shown to significantly enhance golf swing by increasing longer drive distances (12) and augments PP in sprint
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cycling (5). Similarly, VbX warm-up can enhance bat speed in baseball when vibration is combined with lower and upper-limb exercises (35). The discrepancy between the results of this study and of the aforementioned literature may be attributed to methodological differences and the type of performance being investigated. In this study, we attempted to match the number of repetitions and sets for all 3 warm-up conditions; although, VbX-WU took longer to complete compared with DL-WU and Control, the total duration of the vibration exposure was only 90.5 seconds, which may have been insufficient to elicit the required neuromuscular responses. In comparison, other successful sporting VbX warm-ups have implemented longer intermittent vibration exposures that have totaled 4 minutes (12) and 7 minutes (35). Muscle force and power have been reported to be potentiated after acute VbX, where the effects of VbX are postulated to be synonymous with conventional resistance and explosive power training (9,13). This claim is based on the assumption that neural factors, similar to those neural changes seen in the initial stages of traditional resistance and power training, are responsible for the increases in force and power. Vibration exercise is capable of increasing muscle activity (2,36), where the excitatory responses of the muscle spindle may play a role in enhancing muscle activation (34,36). Therefore, we speculated that VbX warm-up would greatly enhance neuromuscular activity and augment DL PO more than a DL-specific warm-up and Control would. However, the EMG activity revealed no difference between the 3 warm-up conditions, suggesting that the magnitude of VbX and loading intensity of DL may have been insufficient to influence neural factors beyond that of body-weight squats (Control) to enhancing DL performance. The literature recommends that, to elicit postactivation potentiation (PAP), resistance exercises should be performed with maximal or near maximal loading (25); however, the loading regime remains equivocal because of inconsistent findings of increased or no change in performance (40). Although no measures of PAP were taken during this study, it is plausible that PAP could account for the current
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Journal of Strength and Conditioning Research findings. Postactivation potentiation has been documented after VbX (18,31), submaximal loads (14,37), heavy loads (3–5RM) (27,30), and recent research has shown that using low-intensity body-weighted exercises significantly improved explosive power compared with using VbX-WU and no warm-up (20). The proposed mechanism of PAP includes motor unit excitability, phosphorylation of myosin regulatory light chains, and pennation angle (40). Alternatively, the warm-up conditions may have lacked the necessary stimulus to elicit PAP; the lack of a pre–warm-up performance measure because of safety considerations means that it is unclear whether any of these protocols elicited PAP. The current warm-up conditions were influenced by various practical considerations: it is not feasible to perform maximal or near maximal efforts because this could induce fatigue and affect our main outcome measures related to lifting performance; to replicate training and competition, it is common practice for lifters to use a DL-specific warm-up regime only; therefore, we deliberately did not include an aerobic component in the current warm-ups. However, excluding the aerobic component may have conserved valuable energy, but it may have caused a detrimental effect where temperature-related warm-up factors, such as muscle temperature and nerve conduction velocity, had little chance of being elevated. According to Bishop (8), short-duration performance enhancement is largely attributable to muscle temperature, and the availability of high-energy phosphates such that the warm-up needs to be of sufficient intensity and duration to maximize the increase in muscle temperature, in the absence of fatigue. It was beyond the scope of the study to measure temperature-related mechanisms, but the exclusion of the aerobic component and the brevity in duration of the current protocols may explain why all 3 warm-up conditions had similar findings. This was probably because of the inability to raise muscle temperature to an adequate level, and thus prevents an increase in subsequent DL performance. Previous work has indicated that 5 minutes of continuous VbX (26 Hz, 6 mmp-p) increased muscle temperature by 1.58 C and enhanced vertical jump performance by 8% (19). The recommendations of the American College of Sports Medicine (3), National Strength and Conditioning Association (6), and American Society of Exercise Physiologists (ASEP) (11) indicate that a general warm-up (5– 10 minutes, 40% V_ O2max) should precede a specific warm-up before undertaking maximum strength testing (1). Recently, it has been reported that a general warmup using cycle ergometry performed at a longer duration (15 minutes) and low intensity (40% V_ O2max) significantly improved 1RM leg press compared with the recommended duration of 5–10 minutes at low intensity (7). However, it may not be practically feasible to implement an aerobic component, especially when time is limited or repeated lifts are required over extended periods, such as in strength- and
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power-based events. In these instances, maintenance of muscle temperature at a reasonable level, while minimizing energy cost, may offer the best solution for performance enhancement. There is a possibility that psychological preparation (psyching up) before lifting the submaximal DL load (75% 1RM) may have activated higher motor centers thus overriding any warm-up effect that the 3 conditions may have had. Although the effects of “psyching up” before maximal effort resistance exercise are equivocal (41), there have been anecdotal reports where moderateheavy loads have been lifted successfully with minimal or no warm-up indicating that higher commands may be responsible for completing such efforts. Further, it is important to note that the current DL-WU protocol had a higher volume compared with the recommended warm-up guideline for 1RM testing (11). Nevertheless, because lifters have their own warm-up routine, which may vary in sets, repetitions, and loading, further research is warranted to investigate whether a range of DL-WU loads (heavier) and different VbX parameters can further influence DL performance. The optimal load for maximizing PO during the DL is not well known, particularly across a range of athletes with different training backgrounds and strength levels. In highly trained powerlifters, DL PP has been shown to occur at a load equivalent to 30% 1RM (39). With this load, Swinton et al. (39) reported PP in excess of 4,300 W, while at a similar load (70% 1RM) to that used in this study, they reported PO approximately twice the PP of this study. Given the lack of consensus for PP in the DL, and other movements, across populations, a “bandwidth” of loads that maximizes PO has been suggested (19); the load used in this study was at the upper end of this suggested “bandwidth.” Clearly, further investigation of PO in the DL is warranted. In conclusion, previous research has indicated that VbX warm-up can enhance sporting performance (5,12,32,35), but the results of this study indicate that for short-term activities, such as deadlifting, VbX-WU produces a muscular performance similar to that of a specific DL-WU and bodyweight squatting (Control). This further suggests that increasing muscle temperature, via aerobic exercise, is probably the most important factor to enhancing subsequent short-term performance (8), unless an appropriate load can guarantee a PAP response.
PRACTICAL APPLICATIONS The current findings suggest that, in the absence of an aerobic warm-up component, body-weight squats, with or without VbX, bring about similar PP outputs as those occurring after a DL-specific warm-up. Therefore, when the training load is submaximal in nature and the intention is to develop high POs, the incorporation of movements specific to the planned lift, irrespective of external load or stimulus, should be encouraged during the warm-up. VOLUME 29 | NUMBER 4 | APRIL 2015 |
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Vibration and Deadlift Warm-Up Warming up before training and competition is often determined by the practicalities and requirements of the sport; the results of this study support the continued use of a progressive DL-specific warm-up to assist the athlete in reaching an appropriate level of preparedness, even if it may come with an additional physiological cost.
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