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Effect of Supportive Equipment on Force, Velocity, and Power in the Squat

Blatnik, Justin A.; Skinner, Jared W.; McBride, Jeffrey M.

Journal of Strength and Conditioning Research: December 2012 - Volume 26 - Issue 12 - p 3204–3208
doi: 10.1519/JSC.0b013e3182736641
Original Research

Blatnik, JA, Skinner, JW, and McBride, JM. Effect of supportive equipment on force, velocity, and power in the squat. J Strength Cond Res 26(12): 3204–3208, 2012—The purpose of this investigation was to examine various kinetic and kinematic variables associated with squats without and with the use of a squat suit (SS). No previous investigation has examined the effect of an SS on squat performance. Participants were 8 elite or professional level male powerlifters (height = 178.59 ± 3.5 cm; body mass = 106.8 ± 30.4 kg; age = 25 ± 2.2 years; mean 1 repetition maximum [1RM] =197.7 ± 53 kg). Subjects participated in 3 testing sessions, with the first session involving a 1RM squat without a squat suit (NSS). Sessions 2 and 3 involved a testing session completing 2 trials in the squat at 3 intensities (80, 90, and 100% of 1RM) either without (NSS) or with an SS. The session and order of the intensities were all randomized. Force-time, velocity-time, and power-time graphs were calculated from data from a force plate and 2 linear position transducers attached to the barbell. Peak eccentric force was significantly higher during SS at 100% of 1RM (NSS-100 = 3196.2 ± 470.6, SS-100 = 3369.7 ± 589.9 N). Peak concentric velocity was significantly higher during SS in comparison to NSS at all intensities. Peak concentric power was significantly higher during SS at 80% of 1RM (NSS-80 = 1566.5 ± 388.4 W, SS-80 = 1770.4 ± 483.2 W) and 90% of 1RM (NSS-90 = 1493.1 ± 296.2 W, SS-90 = 1723.8 ± 449.5 W). The current investigation has demonstrated significantly different kinetic and kinematic characteristics between squats without (NSS) and with an SS, which could ultimately aid in enhancing squat performance.

Neuromuscular Laboratory, Department of Health, Leisure, and Exercise Science, Appalachian State University, Boone, North Carolina

Address correspondence to Jeffrey M. McBride, mcbridejm@appstate.edu.

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Introduction

The sport of powerlifting, which requires lower body strength to lift maximal weight for competition (10), often involves the use of supportive equipment, the most common being a squat suit (SS). The SS has the same fit and design of a singlet used in weightlifting, composed of various materials that stretch and constrict during the movement to possibly aid in lifting more weight. However, no scientific data exist to substantiate this claim. Theoretically, the SS material stretches and stores elastic energy during the eccentric phase of the lift, and the elastic energy may then be released during the concentric phase enhancing the ability to lift heavier weight via increasing force, velocity, and power (3). Thus, the hypothesis for this investigation was that an SS would significantly increase the peak force, velocity, and power during the squat at different percentages of an individual’s 1 repetition maximum (1RM).

Miletello et al. (10)examined the kinematic variables between collegiate powerlifters, high school powerlifters, and novice powerlifters and determined variation in concentric acceleration rates between the 3 groups during various points in the lift. Specifically, the data indicated that the more experienced powerlifters, who lifted more weight, achieved higher velocities in the concentric phase when compared with the novice and high school lifters (3). This data suggests that if supportive equipment, such as the SS, could increase concentric velocity, then this may increase the amount of weight lifted as well. Although no investigations have looked specifically at the SS, some studies have examined the effect of compression garments, such as shorts, on jumping performance. One investigation determined that with the use of a custom-fit compression garment, power was increased in the vertical jump (3). In addition, skin temperature increased at a faster rate during the warm-up protocol and increased flexion and torque rates during sprints and resulted in a reduction of impact forces by 27% in comparison to traditional athletic wear (3). Another study suggests performance enhancement when wearing compression garments during simulated sporting events such as netball (5). Although the SS and compression garments are not the same, they both consist of some similar characteristics, allowing for speculation as the benefit of an SS on squat performance.

The squat is considered to be a closed kinetic chain exercise (1), meaning that during the squat, the load applied during the movement is on the body; however, the force generated is applied to the ground through the bottom of the foot and not necessarily the bar. Depending on the load, the spine can be placed under an excessive amount of compression force. Research suggests that the absolute angle of the spine increased to a nonsignificant 6° from when subjects lifted a load up to 32% of their 1RM (6). However, when using a weight between 40 and 70% 1RM, a significant 16° increase in forward inclination was noted (11). These results were found while performing squats without the use of a squat suit (NSS). Thus, the use of an SS may alter the amount of spine angle change or forward inclination to influence bar path and possibly influence force, velocity, and power. Difference in bar path between a bench press without and with a bench press shirt indicated that the bench press shirt created a more efficient movement pattern by minimizing horizontal displacement (12). Fry et al. (4) examined joint kinetics occurring when forward displacement of the knees is restricted vs. when such movement is not restricted in the squat. The results suggest that when performing a restricted squat where the knees are not permitted to move anteriorly past the toes, greater torque is generated at the hips and less torque at the knees than when performing an unrestricted squat in recreationally weight-trained men (4). This may indicate that when using an SS, which might restrict motion, it would possibly influence the use of additional hip musculature, thereby increasing force, velocity, and power. A study examining national level powerlifters in comparison to recreationally trained lifters indicated that powerlifters moved their knees anteriorly to a lesser degree and generated more knee extensor torque (9). Thus, restricted anterior motion of the knee, possibly as a result of using an SS, might increase the generation of both knee and hip torque.

Based on previous investigations, it appears that garment compression, such as that created by an SS, might increase performance characteristics of a given movement pattern. In addition, changes in bar path, as a result of using an SS, might indicate changes in body or knee position that might allow for increased torque production around the knees and hips. As a result, all these factors might be represented by differences in eccentric or concentric levels of force, velocity, and power. Therefore, the purpose of this investigation was to examine the effect of squatting without (NSS) and with an SS on various kinetic and kinematic parameters to address the hypothesis that an SS would significantly increase the peak force, velocity, and power during the squat.

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Methods

Experimental Approach to the Problem

This study was designed to determine the impact an SS would have on peak force, velocity, and power during a squat performed at 80, 90, and 100% of 1RM. Powerlifting often involves the use of supportive equipment, the most common being an SS, which is surmised to increase squat performance. However, no scientific data exist to substantiate this claim. It is possible that SS material stretches and stores elastic energy during the eccentric phase of the lift. The elastic energy may then be released during the concentric phase, enhancing the lifting ability (3).

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Subjects

Eight elite or professional level male powerlifters who displayed competent technique in using an SS and a minimum of 4 years of resistance training and powerlifting experience were used for this investigation. All subjects have qualified and competed at national events in the Southern Powerlifting Federation and American Powerlifting Federation. All subjects have performed over 318 kg squats with an SS, knee wraps, and weightlifting belt. The subjects had a mean height of 178.59 ± 3.5 cm, a mean mass of 106.85 ± 30.4 kg, a mean age of 25 ± 2.2 years, and a mean nonequipped 1RM squat of 197.7 ± 53 kg. Recruitment of subjects was limited to those who have had no prior injury or surgery of any kind within the last year. The participants were notified about the potential risks involved and were given the opportunity to provide their written informed consent, approved by the Institutional Review Board at Appalachian State University.

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Study Design

The testing was divided into 3 sessions, each session separated by at least 1 week. Participants were asked not to perform any lower-body activity 48 hours pre and post testing to ensure minimal fatigue and adequate recovery between the multiple sessions. During session 1, maximal strength was assessed through 1RM testing in the squat without the use of a squat suit (NSS). Sessions 2 and 3 involved, in a randomized order, squatting either without (NSS) or with an SS. Two repetitions with 5 minutes of rest between each repetition were recorded for trials using 80, 90, and 100% of 1RM also in a randomized fashion. Each participant used a suit that was tailored to fit the subject by Inzer Advance Designs, Inc. (Longview, TX, USA), based on the subject’s height and measurement of the waist, hip, chest, and upper thigh. The suits used in testing were composed of 2 layers of canvas and 2 layers of polyester side panels. Thus, the independent variable was the condition of NSS or SS, and the dependent variables measured were peak force, peak velocity, and peak power for the eccentric and concentric phase of the lift.

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Squat 1 Repetition Maximum Testing

A squat 1RM was assessed after an appropriate warm-up protocol. The warm-up protocol (7) will consist of multiple repetitions at loads equal to 30% (8–10 repetitions), 50% (4–6 repetitions), 70% (2–4 repetitions), and 90% (1 repetition) of the subject's estimated 1RM. During all attempts, subjects were required to lower the bar to a point where the knee angle was 70° as measured by a goniometer. To ensure all squat attempts were performed to the same depth, an adjustable box was placed at the level of the buttocks for each subject. Subjects were given up to 4 maximal attempts to achieve a 1RM. Subject’s foot placement, bar position, and rack height were recorded and used for the remaining testing sessions until the subject completed the study. It is important to note that the subjects were instructed to perform the 1RM testing in the same style of foot placement and bar position as if they were squatting in the SS. Rest periods of 5 minutes were allowed between trials. The maximal load successfully lifted was selected and used to determine the percentages for all subsequent testing sessions.

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Data Collection and Analysis

All testing was performed with the subjects standing on a force plate (BP6001200; AMTI, Watertown, MA, USA) with the left and right sides of the barbell attached to 2 linear position transducers (LPTs) (PT5A-150; Celesco, Chatsworth, CA, USA). The data from the right side of the bar were used for analysis. Analog signals from the force place and 2 LPTs were collected for every trial at 1,000 Hz using a BNC-2010 interface box with an analog-to-digital card (NI PCI-6014; National Instruments, Austin, TX, USA). LabVIEW (Version 8.2; National Instruments) was used for recording and analyzing the data. Signals from the 2 LPTs and the force plate and data derived using double differentiation underwent rectangular smoothing with a moving average half-width of 12. From laboratory calibrations, the LPTs and force plate voltage outputs were converted into displacement and vertical ground reaction force, respectively. Kinetic and kinematic variables were derived from displacement data through double differentiation processes. Bar displacement was measured using 1 of the 3 LPTs mounted directly above the subject on a custom power rack. The LPT produced a voltage signal representative of the degree at which the LPT was extended, allowing for displacement-time data to be calculated. Subjects were fitted with an inline mechanical goniometer sensor (NORAXON USA, Inc., Scottsdale, AZ, USA) to ensure that the appropriate knee angle was achieved during the various trials. The goniometer produced voltage outputs that were converted into knee angles found by creating a regression equation. If the squat did not meet the selected criteria for the trial, then it was thrown out and another squat was performed. The force plate methodology has been extensively examined throughout the literature to evaluate force and power produced during dynamic movements such as the squat (2). From force plate and LPT data, force-time, velocity-time, and power-time curves were created. Peak values were then obtained for comparison. Test-retest reliability has been previously reported for this method at r = 0.95 (2).

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Statistical Analyses

Descriptive data was summarized as mean ± SD. Differences between kinetic and kinematic variables were determined through a repeated measures general linear model. The criterion alpha level for all statistics was set at p ≤ 0.05. All statistical analyses were completed using a statistical software package (SPSS Version 17.0; SPSS, Inc., Chicago, IL, USA).

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Results

Peak concentric forces were not significantly different between NSS and SS at all intensities (NSS-80 = 3459.8 ± 510.8 N, SS-80 = 3594.5 ± 638.9 N, NSS-90 = 3630.5 ± 522.7 N, SS-90 = 3770.2 ± 622.3 N, NSS-100 = 3767.1 ± 523.2 N, SS-100 = 3828.0 ± 493.3 N). However, during the 100% trial, eccentric force was significantly higher in SS, which can be observed in Figure 1 (NSS-80 = 2952.1 ± 462.9 N, SS-80 = 3018.3 ± 617.9 N, NSS-90 = 3047.2 ± 484.0 N, SS-90 = 3103.1 ± 608.3 N, NSS-100 = 3196.2 ± 470.6 N, SS-100 = 3369.7 ± 589.9 N). The confidence interval (CI) for eccentric peak force at 100% was NSS 2,791–3,600 N and SS 2,965–3,774 N, with an effect size of 0.92. Concentric velocity was significantly higher during squats at all intensities with the SS when compared with NSS shown in Figure 2 (NSS-80 = 0.548 ± 0.135 m·s−1, SS-80 = 0.616 ± 0.113 m·s−1, NSS-90 = 0.493 ± 0.117 m·s−1, SS-90 = 0.567 ± 0.119 m·s−1, NSS-100 = 0.413 ± 0.127 m·s−1, SS-100 = 0.462 ± 0.112 m·s−1). The CIs for concentric peak velocity at 80, 90, and 100% were 80NSS 0.46–0.65, 90NSS 0.41–0.59, 100NSS 0.32–0.50, 80SS 0.52–0.71, 90SS 0.48–0.66, and 100SS 0.37–0.55, with effect size of 1.5, 1.76, and 1.17, respectively. There was no significant difference in eccentric velocity (Figure 2) (NSS-80 = 0.020 ± 0.012 m·s−1, SS-80 = 0.021 ± 0.001 m·s−1, NSS-90 = 0.020 ± 0.001 m·s−1, SS-90 = 0.020 ± 0.001 m·s−1, NSS-100 = 0.011 ± 0.001 m·s−1, SS-100 = 0.020 ± 0.010 m·s−1) and eccentric power (Figure 3) (NSS-80 = 59.3 ± 0.1 W, SS-80 = 62.5 ± 0.1 W, NSS-90 = 47.8 ± 0.1 W, SS-90 = 56.7 ± 0.1 W, NSS-100 = 36.1 ± 0.1 W, SS-100 = 56.8 ± 0.1 W) between NSS and SS. However, concentric power was significantly higher with the SS during the 80 and 90% trials (Figure 3) (NSS-80 = 1,566.5 ± 388.4 W, SS-80 = 1,770.4 ± 483.2 W, NSS-90 = 1,493.1 ± 296.2 W, SS-90 = 1,723.8 ± 449.5 W, NSS-100 = 1,322.6 ± 390.0 W, SS-100 = 1,453.1 ± 278.8 W). The CIs for concentric peak power at 80 and 90% were 80NSS 1,234–1,899, 90NSS 1,204–1,782, 80SS 1,438–2,103, and 90SS 1,435–2,012, with an effect size of 1.31 and 1.70, respectively.

Figure 1

Figure 1

Figure 2

Figure 2

Figure 3

Figure 3

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Discussion

There are currently no investigations that have been reported on the biomechanical implications of using an SS, examining the differences in peak force, velocity, and power. Previous research has shown that velocity in squats has a direct relationship on the amount of force exerted and thus indicative of subject technique and therefore was considered the most meaningful parameter regarding performance (10). The primary findings in the investigation indicate that squats with SS elicited higher velocity and power during the concentric portion of the exercise. It is theorized that this is because of the suit’s ability to store elastic energy during the eccentric phase of the squat and its release in the concentric phase. One can see the same effect with squats that use the stretch-shortening cycle (8). The SS allows the individual to maintain a higher power output at lower intensities when compared to the squats without the suit (NSS). The SS allows for a higher velocity at all intensities compared with the NSS condition. These results coincide with past research (9) and the initial hypothesis that the suit would enhance these variables. Although there was a difference in peak concentric force within the 2 conditions, they were not significant. This is surprising given the fact that most competitive powerlifters are able to increase their 1RM with the SS. It should be noted that the loads used in this investigation are typically lower than those used while training in the SS. Although not reported, greater absolute loads would likely result in altered kinetic and kinematic variables. Further study would be necessary to determine the role of different relative loads on the kinetic and kinematic variables measured.

As mentioned previously, through analysis of data, authors have indicated that the more experienced powerlifters, who lifted more weight, achieved higher velocities in the concentric phase when compared with the novice and high school lifters (3). In addition, scientists studying compressive garments elude to the possible performance-enhancing effects including jumping power and skin temperature (3) and performance in sporting events such as netball (5). The SS may have altered some of the kinematic variables associated with performing the squat in terms of body or leg position. No data exist concerning body mechanics with an SS, but some related studies might indicate how these differences might influence force, velocity, and power output. Wretenberg et al. (13) looked at the differences associated with high and low bar squatters in powerlifters and weightlifters. Their results determined that powerlifters who used the low bar position put relatively more load on the hip joint, whereas the weightlifters had the load disturbed equally between the hip and the knee. It is likely that the SS allowed the lifters to remain more upright during the squat relative to their hip position compared with the NSS squats that caused the anterior inclination of the torso (4) and possibly excess vertical displacement.

McLaughlin et al. (9) found similar results when examining a highly trained powerlifter; they found that trunk, hip, and knee horizontal displacements were greater in the less skilled group and could elicit a decrease in performance. This suggests that SS helps to minimize these variables and help increase squatting performance. These results may not be typical when using novice lifters or powerlifters who compete without the use of the squat suit (NSS) in training and competition. Further study would be necessary to determine the role relative experienced lifters had on the kinetic and kinematic variables measured. Although not reported in the current investigation, the material and structure of the suit could have implications on the different kinetic and kinematic variables. This being the first investigation comparing the different variables of the squat exercise without (NSS) and with the use of an SS, future research will help to best delineate how to use the SS during the course of an athlete’s training program and competition to maximize performance.

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Practical Applications

The most appropriate application of the SS would be its use in powerlifting competition. The increased velocity and power values observed in this investigation do suggest that there is an increase in the potential to lift heavier weight when using SS. It is unclear whether incorporating SS into training would positively augment strength and power because there is no data available concerning training implications. Coaches for powerlifting should be aware that an SS does appear to increase squat performance and might consider the use of an SS either in training or in competition as a way to enhance performance.

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References

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Keywords:

strength; exercise; performance; athlete

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