The bench press is one of the most used exercises within strength and conditioning practice and programming (22). Similar to other free weight resistance exercises, the bench press is used for developing maximal strength, power, and hypertrophy (31). The bench press is also one of the 3 competition lifts within the sport of powerlifting (IPF, 2015). However, the popularity of the bench press is because of its ability to develop the strength, power, and hypertrophy of the prime movers: the pectoralis major, anterior deltoid, and triceps brachii (13,21,24,26). Several studies demonstrate the transfer of bench press strength to improvements in motor unit recruitment through various planes of the shoulder (13,14), and more importantly for athletic performance, strength in the bench press is an indicator of performance in strength and power sports (10,11,23). Therefore, developing strategies to improve bench press performance has the potential to improve performance across a range of sports including but not limited to powerlifting, discus throwing (10), swimming (11), and kayaking (23).
When training for an increase in strength, several training methods and strategies can be adopted. With regard to specificity and technical practice, it is important to perform the full movement itself; however, there is a growing trend to use supplementary or assistance training to develop the muscles, movement patterns, or weak points within a given exercise (29,30,35). A recent survey of competitive powerlifters demonstrated that more than 50% are using resistance bands in their bench press training, more so than alternative supplementary training methods such as the use of chains (30).
Elastic resistance training primarily involves the use of elastic bands of varied thicknesses to challenge a movement pattern and align with the force capability of the musculature throughout the range of motion of many movement tasks (29,35). Several studies demonstrate that the use of combined elastic resistance training in the bench press improves the development of upper-body strength (1,8,13,18), and in addition, a recent meta-analysis supports the efficacy of variable resistance training methods (use of bands and chains) to improve measures of maximal strength (28). Despite the increased popularity and evidence for the use of elastic resistance training, far less attention has been focused on elastic assistance training.
Elastic assistance training uses an assistance or an overspeed approach during the performance of athletic and strength training movements, allowing an athlete to run faster, jump higher, or lift more weight than they could do without the assistance (7,32). Several studies demonstrate that elastic assistance acutely improves jump height (32) and sprinting performance (7), whereas chronic jump training with elastic assistance for 4 weeks significantly improved jump performance compared with training without assistance (3). Relative to research on elastic resistance devices, much less attention has been given to the implementation of elastic assistance devices for upper-body strength performance.
A recent study examined the acute effects of implementing a supportive assistance device called the “Slingshot (SS),” on 1 repetition maximum (1RM) bench press performance in 19 resistance trained male participants (36). The study observed the effect of the “SS” in comparison with traditional “Raw” bench press performance, and report significant increases to 1RM and barbell velocity associated with trends for decreased electromyographic (EMG) amplitude for both the pectoralis major and triceps brachii. They reported that all participants showed an increase in absolute 1RM performance by an average of ∼16 kg while wearing the “SS,” and that participants were able to execute their “Raw” 1RM weight at significantly higher barbell velocity and power output when using the “SS.” However, when the relative intensity was matched between the absolute “Raw” vs. “SS,” 1RM average barbell velocity and average power output were not statistically different and there was a trend for the prime mover normalized EMG amplitude to be lower while wearing the “SS” despite the heavier load. These data indicate that the “SS” was assisting participants to lift either heavier loads or equal loads at a greater velocity, whereas the trends for decreased EMG amplitude suggest potential deloading in the prime movers.
We therefore assessed bench press kinematics and neuromuscular activation during maximal and submaximal bench pressing with or without the “SS” in trained powerlifters. Our aim was to use stick point analysis (9,33) in conjunction with EMG assessments to try to understand the mechanism by which the “SS” improves 1RM, and the influence it may have on matched intensity submaximal sets. We hypothesized that the improvement in 1RM with the “SS” would be because of either (a) an increased normalized surface EMG (sEMG) amplitude of the prime movers during or after the stick period of the bench press or (b) that the improvement would be because of a greater peak and average velocity in the early phases of the bench press as a result of the elastic assistance provided by the “SS.” As a secondary hypothesis, we also theorized that the “SS” would maintain barbell velocity during sets with multiple repetitions.
Experimental Approach to the Problem
This study used a within-subjects design to examine the effects of Mark Bell's original “SS” on maximal and submaximal bench press kinematics and neuromuscular activity. The study was designed to assess how using the elastic assistance device, the “SS,” altered neuromuscular recruitment patterns of the prime movers and the kinematics of the bench press during maximal and submaximal efforts. These measurements will allow us to determine the mechanism by which the “SS” may be working and illustrate what affect it may have on muscle recruitment.
The methods and procedures implemented within this study were approved by the University of Stirling, School of Sport Research Ethics Committee, and all participants provided written informed consent on recruitment selection. All testing took place at the Gannochy Sports Center—Athlete Performance Laboratory, at the University of Stirling, United Kingdom. Fifteen male competitive powerlifters (Table 1; subject characteristics) voluntarily participated in this study. Participants were contacted through word of mouth, social media, and through study advertisement from 2 drug-tested powerlifting federations within the United Kingdom. Participants were selected based on having ≥2 years of powerlifting-based strength training. All participants were considered healthy and injury-free based on their responses to a Physical Activity Readiness Questionnaire and understood no reason as to why their ability to exert maximal bench press force would be limited in any way.
The study consisted of 2 laboratory-based trials of ∼1.5 hours each. Trials were scheduled between 7 to 14 days apart and were completed at the same time of day to account for circadian variation (4). During each trial, participants' 1RM bench press was measured, followed by a predicted 3RM (3Rep) at 87.5% of achieved 1RM and 3 submaximal sets of 8 repetitions (8Rep) at 70% of achieved 1RM (2). All participants completed the “Raw” trial first (without the use of the SS), followed by the “SS” trial.
All bench press attempts were completed on a solid leather competition height bench secured in position inside a FT700 Power Cage (Fitness Technology, Melbourne, Australia), and using an IPF specification Eleiko PL competition barbell (Eleiko, Halmstad, Sweden), Eleiko WL colored training disks (Eleiko), and Eleiko Olympic WL competition collars (Eleiko).
Before commencing the initial trial, participants were provided with a 3-day training and food diary, and asked to complete both diaries in the 2 days leading up to, and day of testing. Participants were advised to maintain their normal diet and training habits and to avoid completing the bench press exercise 48 hours before testing. Before the second trial, participants were provided with their original diaries and advised to replicate their activities to the upmost of their ability.
On arrival to the laboratory, participants provided anthropometric measurements comprising their age (years), body mass (kilograms), and height (centimeters), along with a competition-style bench press 1RM (kilograms) predicted to the best of their ability. Participants were also allowed to select their preferred rack height, and demonstrated their bench press grip width, which was measured and recorded (centimeters) and marked for reference on the barbell using masking tape.
Before commencing any warm-up activities, participants were familiarized with the testing protocol and requirements, and allowed to ask any questions or for any further information, if required. During the initial phase of the warm-up, all participants were required to familiarize themselves with the sEMG normalization procedure by completing controlled and consistent bench press repetitions using the empty barbell to a metronome set at 30 b·min−1, before loading. During this familiarization, a clearly audible metronome was played through a pair of speakers, and participants were required to complete a full competition style set-up, unrack the barbell, and perform as many repetitions as they deemed necessary until they felt confident executing the bench press movement to the rhythm of the metronome. Each time the metronome sounded indicated a change of phase (eccentric:concentric), requiring a controlled time period of 2 seconds per phase.
After the metronome familiarization, the barbell was loaded for participants and they performed repetitions at various increments of their choosing. Number of sets, repetitions, and loadings were recorded on a data collection sheet for replication in the subsequent trial and rest intervals of 2 minutes were provided throughout the warm-up. For normalization purposes, participants were recorded performing 1 set of 5 repetitions at 70% of predicted 1RM to the 30 b·min−1 metronome, following the criteria highlighted above (6). After the single normalization set, participants continued with their own self-selected warm-up.
Once participants exceeded 90% predicted 1RM, all attempts were considered “1RM attempts” and were completed between 5-minute rest intervals and to correct referee commands and competition rules (IPF, 2015). Participants proceeded with 1RM attempts in increments of their choosing and in agreement with the primary investigator until they reached muscular or technical failure. In all instances, 1RM was achieved between 3 and 5 attempts. Attempts were disqualified if the participant failed to successfully perform the repetition or if they failed to meet all competition requirements for successful bench press performance (IPF, 2015) (Figure 1). Once participants had established a 1RM, they performed 3 consecutive paused repetitions at 87.5% 1RM to demonstrate execution of a predicted 3 repetition maximum (3Rep) with consideration to fatigue accumulated following the 1RM protocol (2). Participants finally completed 3 sets of 8 continuous and dynamic repetitions (8Rep) using 70%1RM (2). Multiple repetition sets were also separated by a 5-minute rest interval and assistance racking and unracking the barbell was provided at the participants' choosing.
Following the 7- to 14-day interval, participants returned to the laboratory and completed the SS trial. Participants were provided with an introduction to the SS, and, identical to trial 1, participants' anthropometric characteristics were taken and a refamiliarization to the procedures was provided before commencing the warm-up. Several different size selections were provided for the “SS” device, and were fitted to each participant according to the manufacturer's instructions. The same warm-up protocol was followed, and an identical rack height and grip width was implemented. All warm-up before, and including normalization repetitions were taken without the use of the “SS,” and all repetitions performed following the 70% normalization were completed using the “SS.” The “SS” was worn across the elbow joint as recommended by the product manufacturers, and to avoid disruption to EMG signals on the triceps and pec placements (Figure 2). The achieved Raw 1RM weight was performed as one of the “SS” 1RM attempts (Raw max/SS), participants then proceeded to add weight and follow the same protocol as the “Raw” trial until a separate “SS” 1RM was achieved. Participants' 3Rep and 8Rep weight were established using 87.5% and 70% of the achieved “SS” 1RM, respectively, and were performed in the same manner described for the “Raw” trial. All attempts throughout both trials were performed to the nearest 1 kg.
Surface EMG amplitude was collected by skin surface electrodes (SilveRest, Vermed, VT) from the pectoralis major, anterior deltoid, and triceps brachii of the participants' dominant side during all repetitions using a BioPac MP100 (BioPac Systems, Inc., Santa Barbara, CA, USA). Reference signals were provided via skin surface electrodes placed on the clavicularis and patella. Before applying the electrodes, the skin surface was prepared for collection by shaving, slightly abrading using sandpaper, and wiped with alcohol swabs (PDI Healthcare, Orangeburg, NJ, USA), in line with SENIAM guidelines (16). A small amount of SignaGel electrode gel (Parker Laboratories, Fairfield, NJ, USA) was used on the center of each electrode to aid signal quality. Electrodes were applied to the skin surface ∼2 cm apart and secured to the skin surface with masking tape, if necessary. Because of the nature and placement of the “SS,” electrodes for the pectoralis major were placed using medial and central clavicularis placements as suggested by Krol et al., (19) (Figure 2). Electrode placement for both the anterior deltoid and triceps brachii were in line with recommendation by Perotto and Delagi (25). As participants performed bench press repetitions, the EMG amplitude of the pectoralis major, anterior deltoid, and triceps brachii (root mean square; RMS) was collected using the Acqknowledge software for Windows (BioPac Systems, Inc.) and saved for offline analysis.
A Celesco PT5A-125-S47-UP-10K-M6 linear transducer (Celesco, Toronto, ON, Canada), connected to a BioPac MP100 data capture unit (BioPac Systems, Inc.), was secured to the top of the power rack to measure participants' average barbell velocity (m·sec−1) and bar displacement (centimeters) during all bench press attempts. During both “Raw” and “SS” trials, a Velcro strap attached to the transducer cable was secured in a consistent, slightly off center placement on the barbell. The position of the transducer was adjusted appropriately for each participant so that the cable ran vertically during bench press execution. As participants performed bench press repetitions, the velocity and displacement of the barbell was recorded using the Acqknowledge software for Windows (BioPac Systems, Inc.) and saved for offline analysis.
All data were analyzed using the Acqknowledge software for Windows (BioPac Systems, Inc.). Repetition phases were defined in accordance with (9,34). Surface EMG signals for the pectoralis major, anterior deltoid, and triceps brachii were digitized individually at a sampling rate of 2,000 Hz and recorded in volts. Surface EMG signals were RMS processed based on previous recommendations for research investigating neuromuscular activation levels (15). Average RMS was calculated for a moving window 100-millisecond time period across the entire waveform for each activity. The sEMG signals were then normalized against corresponding repetitions extracted from the set of 5 reps performed to a metronome at 70% 1RM (6) as part of the participants' warm-up.
Analysis of the transducer data was performed by highlighting only the concentric phase of the repetitions. Phases were defined in accordance with Van den Tillaar and Ettema (34). For both maximal and submaximal repetitions, the start of the concentric phase was identified as the first point at which velocity reached 0 m·sec−1, indicating a change of direction. For maximal attempts, the phases of the concentric portion of the bench press were defined as per Van Den Tillaar and Ettema (34) (Figure 3 for representative trace). This involved defining the beginning of the prestick period (phase 1) by identifying the point at which velocity was 0 m·sec−1 at the end of the eccentric phase, identifying the stick point and beginning of the stick period (phase 2) as the point of peak velocity during the concentric phase, and identifying the poststick period (phase 3) as the point at which acceleration again crossed 0 m·sec−2. The lift ended when velocity reached 0 m·sec−1 at the end of the concentric phase. Each phase and/or repetition was analyzed individually for total time (seconds), average bar speed (m·sec−1), and the stick point was identified (meters) comparative to the total displacement.
All statistical analyses were carried out in GraphPad Prism (GraphPad Software, La Jolla, CA, USA). Where 2 groups were compared, a 2-tailed t-test was performed. Where more than 2 groups were compared, a 1-way analysis of variance (ANOVA) was used with a Tukey's HSD test. Where multiple comparisons were made across groups, a 2-way ANOVA was performed with a Bonferroni's multiple comparisons test. Normality of data was tested using D'Agostinio-Pearson omnibus normality test. Where data were not normally distributed, then the nonparametric 2-tailed t-tests were performed. When multiple comparisons were made on nonnormal data, then a Friedman test was used with a Dunn's multiple comparisons test. All data were reported as mean ± SEM and significance was set as p ≤ 0.05. Correlations were determined via a simple linear regression.
All participants displayed an increase in absolute bench press performance while using the “SS” from 139.7 ± 4.34 kg “Raw” to 160.4 ± 4.43 kg “SS” for an average increase of ∼20 kg (Figure 4A). The absolute gain from the “SS” was not related to the amount lifted (Figure 4B) but instead was highly correlated to the individuals bodyweight (R2 = 0.334), indicating that despite all participants wearing an appropriately sized device, the larger participants were able to gain more from the “SS” (Figure 4C). The “Raw” 1RM corresponded closely to the calculated “SS” 3Rep (Figure 4D). These data were plotted and correlated revealing that there was a highly significant correlation between participant's “Raw” 1RM and “SS” 3Rep (R2 = 0.954) (Figure 4E).
During maximal 1RM bench press attempts, “Raw” normalized triceps RMS (169.64 ± 15.26%) was significantly higher than both “Raw max/SS” and “SS” conditions (87.28 ± 5.84% and 115.84 ± 10.64%) (Figure 5A). Normalized RMS for the pectoralis was significantly lower in the “Raw max/SS” condition compared with the “SS” condition (90.83 ± 6.97% vs. 117.8 ± 11.27%) during 1RM attempts (Figure 5A). Normalized RMS for all muscles (grouped) was significantly reduced during 1RM performance for “Raw max/SS” (95.58 ± 5.47%) than during the “Raw” condition (138.82 ± 9.42%) (Figure 5A). Normalized triceps RMS was also observed to be significantly higher during the “Raw” condition (126.02 ± 9.19%) than the “SS” condition (83.12 ± 9.97%) during a set of 3 repetitions (Figure 5B), and during both set 1 (108.15 ± 6.25% vs. 75.96 ± 7.36%) and set 3 (115.35 ± 7.48% vs. 84.37 ± 8.45%) of the multiple sets of 8 repetitions (Figure 5C).
Average barbell velocity was significantly greater across the whole concentric phase by ∼3-fold for the “Raw max/SS” condition (0.29 ± 0.02 m·sec−1) compared with the “Raw” and “SS” conditions (0.11 ± 0.01 m·sec−1 and 0.10 ± 0.01 m·sec−1) (Figure 6A). The peak velocity during the maximal attempts was significantly higher in the “SS” condition compared with the “Raw” condition (0.31 ± 0.02 m·sec−1 vs. 0.27 ± 0.02 m·sec−1), as was the average velocity of phase 1 (Figure 6A). There is a trend for phase 3 to have a lower velocity in the “SS” condition compared with “Raw.” There is a high degree of variability between the “SS” and “Raw” conditions when plotting these data as individual responses, while during phase 1 there is a consistent increase in phase 1 velocity (9 subjects increase) when wearing the “SS” (Figure 6B).
The displacement data demonstrates that there was no effect of wearing the “SS” on total displacement indicating that hand position was replicated accurately between trials and that the “SS” did not affect the range of motion (Figure 6C). However, the “SS” significantly altered the displacement at which the stick point occurred (Figure 6C). The effect was small, ∼1 cm higher in the concentric phase, but very consistent with 12 of 15 subjects demonstrating an upward shift in the start of the stick point (Figures 6C, D). The sticking period tended to occupy a greater proportion of the concentric phase while wearing the “SS”; however, this did not reach significance. While not significant, when the individual data were plotted as percentage of the total displacement, there was a similar trend but a high degree of intersubject variability, with 7 subjects demonstrating an increase and 8 subjects demonstrated a decrease in the stick period length while wearing the “SS” (Figure 6D).
No significant differences were found for average barbell velocity (m·sec−1) during reps 1 and 2 of the 3Rep; however, the average barbell velocity was significantly faster for the “SS” condition than the “Raw” condition (0.21 ± 0.02 m·sec−1 vs. 0.18 ± 0.02 m·sec−1) during rep 3 of the 3Rep (Figure 6E). Similarly, the change in barbell velocity (%) between reps 1 and 3 of the 3Rep were significantly lower in the “SS” than the “Raw” condition (−15.72 ± 5.36% vs. −25.57 ± 9.4%) (Figure 6F). Average barbell velocity was significantly faster during the “SS” than the “Raw” condition for both set 1 rep 8 (0.35 ± 0.04 m·sec−1 vs. 0.30 ± 0.04 m·sec−1) and set 3 rep 8 (0.34 ± 0.07 m·sec−1 vs. 0.26 ± 0.03 m·sec−1) during the multiple sets of 8 repetitions (Figure 6G). Similarly, the change in barbell velocity (m·sec−1) between reps 1 and 8 of the multiple sets of 8 were significantly lower in the “SS” than the “Raw” condition (−19.38 ± 4.4% vs. −31.18 ± 4.82%) (Figure 6H).
To determine the mechanism behind the improved 1RM performance while wearing the “SS,” we split the analysis of the prime mover RMS over the 3 phases of the bench press; prestick period , stick period , and poststick period . These data revealed that there was no effect of the “SS” on pectoralis (Figure 7B) or deltoid (Figure 7C) RMS activation. However, the triceps RMS was significantly lower during the stick  and poststick  periods (Figure 7A).
This is the first study to assess the impact of the “SS” bench press training aid on bench press kinematics and neuromuscular activity in comptetitive powerlifters across a range of intensities. The “SS” was found to be an effective elastic assistance device for enhancing 1RM bench press performance in all participants, on average producing a fixed absolute increase of ∼20 kg. This elastic assistance allowed the “Raw” 1RM to be lifted with an average velocity ∼3× faster than the “Raw” 1RM performed unassisted. The increased velocity while wearing the “SS” occurred despite significantly reduced RMS in the triceps brachii. Furthermore, when intensity was matched (same relative %1RM with or without the “SS”), the RMS of the triceps was reduced at all intensities. During both the multiple repetition conditions (3Rep/8Rep), the last rep was performed with a higher velocity than the corresponding “Raw” condition. This preservation of barbell velocity throughout a set may be indicative of reduced fatigue (27), suggesting that despite matching for relative intensity, the “SS” may effectively reduce fatigue.
Components of the velocity data from our study are somewhat reminiscent of the velocity data obtained from performing the bench press with chain weight (5). At the beginning of the concentric phase, the assistance from the device will likely be greatest, and like with chains, the force required to move the bar off the chest will be lower with the weight experienced increasing into lockout. Therefore, increased velocity is an attractive theory for the mechanism of how the “SS” may work. Despite the greater load, the average barbell velocity of the maximal lift was the same between conditions, with peak barbell velocity significantly faster during a maximal attempt with the “SS.” Assessing barbell velocity during the different pressing phases revealed that during the prestick period , barbell velocity was significantly faster while wearing the “Slingshot.” The velocity data yield some insight into the mechanism by which the “SS” may allow an individual to complete a full lift with significantly more weight than their “Raw” 1RM. We initially theorized that as the concentric phase progressed, the activation of the prime movers would increase to compensate for the reducing assistance supplied by the elastic device. To our surprise, the RMS of the pectoralis and the deltoids was the same between the “Raw” and “SS” conditions, whereas the RMS of the triceps was significantly reduced in the “SS” trial. These data indicate that despite ∼20 kg extra on the bar, the triceps are having to activate to a lesser extent to complete the lift, even during the poststick  phase of the lift where the assistance from the device would be assumed to be minimal. We hypothesize that the ability to complete the repetition with a significantly greater load during the “SS” trial is driven by both the increased peak velocity, and increased velocity throughout the prestick  period imparting more momentum to the barbell. However, it is unlikely that increased velocity is the mechanism responsible for every individual, as several individuals display a reduced velocity during the prestick period . As a result, we must explore additional theories as to how the “SS” allows individuals to lift significantly higher loads, despite similar, and in some cases reduced, prime mover sEMG.
One possibility is that the “SS” may alter the mechanics of the bench press by pulling the elbows into a more mechanically advantageous position. Van den Tillaar and Ettema (34) suggest that the stick period during the bench press is partly because of the arm position transitioning into a less mechanically advantageous position. It is possible that because of the nature and placement of the “SS,” that it may be maintaining the elbows in a position, which may allow for a stronger press. Another possibility for how the “SS” alters the bench press performance is that the “SS” shifts the displacement at which the stick period begins. While the shift in where the stick period begins was small, ∼1 cm higher during “SS” vs “Raw,” we cannot rule out the possibility that this small shift may have had a significant effect on the ability to complete the lift.
The study by Ye et al., (36), similar to ours, found a fixed increase in 1RM performance from wearing the “SS.” They observed an increase in absolute 1RM performance from 114.6 to 132.1 kg and a fixed mean increase of 17.6 kg while wearing the “SS.” Our findings, however, showed that the “SS” improved mean 1RM bench press performance from 139.7 to 160.4 kg with a mean fixed increase of 20.67 kg. Although largely similar, the slight differences in findings between our study and those of Ye et al., (36) are possibly due to the training status and technical competency of the different sample groups. As in our study, they also found no correlation between the 1RM and the gain from wearing the “SS.” These data indicate that the weight lifted while wearing the “SS” is not related to the amount of weight on the bar. We find, however, that the mass of the individual is significantly correlated to the gain from wearing the “SS.” The range in gain from wearing the “SS” in our study was 15–27 kg with the greatest gain achieved by the largest (by body mass) individual in the study (124.1 kg). We theorize that this effect may be driven by chest girth, i.e., greater chest girth creating a greater stretch producing more elastic assistance. Future studies should correlate more comprehensive anthropometric measures to the gain from wearing the “SS,” thus allowing for an individual to estimate the gain they will get from the device by making a simple anthropometric measure.
Aside from suggesting how the “SS” works, our data also suggest some potential uses for the device in training. Some researchers have theorized that the benefit of elastic training is that it allows for similar forces to be produced but at faster velocities (20). The “SS” could be used as a speed training device, as our data clearly demonstrate that velocity is substantially improved while wearing the “SS.” Therefore, it may have some utility in velocity training for sports such as the shotput. However, the sEMG data shows that the triceps are very likely deloaded at all intensities with the “SS.” These findings combined with the velocity data from the multiple repetition sets suggest that the “SS” likely reduces fatigue and could also be used as a deloading tool. One advantage of the “SS” over other deloading or speed training tools, such as using bands and chains, is its ease of use. Furthermore, unlike other commonly used deloading tools, the “SS” allows for a full range of motion to be performed as demonstrated by total barbell displacement during both “Raw” and “SS” trials. It should be noted that if the “SS” was used for a bulk of training, that the potential deloading of the triceps would very likely lead to a reduced performance on the bench press; therefore, it should be used strategically and as a supplement to traditional bench press training.
In summary, the acute increases observed in bench press performance resultant of using the “SS” suggest that it may be an effective training device for speed training and deloading the bench press exercise during a variety of intensities while maintaining the full range of motion of the traditional format of the bench press.
This study was conducted without any financial support and we have no conflicts of interest. The results of this study do not constitute endorsement of the product by the authors or the NSCA. The authors gratefully acknowledge expert technical assistance for Mr Chris Grigson. The authors are indebted to the volunteers who gave their time to this study.
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