The ability to express high levels of power and speed are essential components of athletic success in numerous sports, including rugby union (1,2,13–15,20,23). Loaded jump squats are a commonly used exercise to stimulate improvements in power output (3,5,21,29). Performance in the traditional barbell jump squat (BBJS) has been shown to be significantly related to sprint acceleration and measures of lower-body power output, such as the countermovement jump (CMJ) (25). An increasingly popular loaded jump squat variation is the hexagonal barbell jump squat (HBJS); however, its relationship with athletic performance is yet to be established.
It is now widely recognized in the literature that the body mass of the participant should be included in the calculation of peak power (8,12,28). When this is taken into account, the amount of external load required to optimize peak power in the jump squat is greatly reduced. Cormie et al. (9) reported peak power output to occur with no external load in the BBJS in a group of 12 elite Division I male athletes. This has been corroborated by a number of research studies all reporting that the optimal load for peak power in the BBJS occurs at body mass alone (1,6,8,11). Swinton et al. (26) compared the use of a hexagonal barbell in the jump squat exercise with the use of a traditional barbell. While reporting that the body mass–only condition produced more power than any BBJS load, peak power in the HBJS occurred at 20% of 1 repetition maximum (1RM) load. This load in the HBJS (20% of 1RM) produced significantly higher levels of peak power compared with the equivalent loaded BBJS condition (4,606 ± 510 W vs. 4,091 ± 438 W). The authors speculated that the positioning of the load, with the resistance at arms' length and closer to the bodies' center of mass, improved the kinematics and kinetics of the HBJS in comparison with the BBJS condition.
The HBJS has received limited attention in the literature despite its practical potential as a means of possibly developing lower-body power in athletes. Based on the findings of Swinton et al. (26), the HBJS may positively alter the force-velocity profile of the jump squat exercise because of the positioning of the external load. The relationship between power output in the BBJS exercise and athletic performance has been extensively examined (4,10,22,25). Cronin and Hansen (10) reported significant correlations between relative peak power in a BBJS and CMJ height in a group of rugby league players. They also reported a significant relationship between relative peak power and 5-, 10-, and 30-m speed times. Similarly, Baker and Nance (4) reported a significant relationship between relative peak power at a range of BBJS loads (40–100 kg) and 10- and 40-m speed time in professional rugby league players. However, despite the potential superiority of the HBJS over the BBJS in the generation of peak power, no research to date has examined the relationship between power output in the HBJS and any aspect of athletic performance.
The aim of this study therefore was to investigate the relationship between peak power output developed during the HBJS (measured at each participant's individual optimal load) and CMJ height and acceleration speed in elite rugby union players. It was hypothesized that peak power output relative to body mass in the HBJS condition would be significantly correlated with acceleration time and CMJ height.
Experimental Approach to the Problem
This study used a 1-group experimental design to investigate the relationship between HBJS relative peak power output, 10- and 20-m sprint time, and CMJ height. The relationship between these variables was quantified using a Pearson product-moment correlation coefficient. Standard multiple regression was used to assess the relationship between HBJS relative peak power output, CMJ height, and 10-m sprint time. The dependent variable was 10-m sprint time with the independent variables being HBJS relative peak power output and CMJ height. A similar procedure was undertaken to investigate the relationship between HBJS relative peak power output, CMJ height, and 20-m sprint time. The dependent variable was 20-m sprint time with the independent variables being HBJS relative peak power output and CMJ height.
Seventeen, professional level, male rugby union players volunteered to participate in the study (age = 21.3 ± 1.3 years, body mass = 98.6 ± 9.4 kg, height = 1.85 ± 0.06 m, box squat 1RM = 187.2 ± 17.1 kg). All players were contracted to a professional rugby union club playing in the Pro12 competition. None of these players had represented their country at test rugby level at the time of the study. Players were recruited on the basis that they were free from any injury or training restriction, as verified by the club physiotherapist and had a minimum of 2 years of structured training experience under the supervision of a qualified strength and conditioning coach. All participants regularly performed maximal acceleration, unloaded jumps, and loaded jumps as part of their training and were familiar and technically proficient with the HBJS variation. Testing was performed during the in-season where typical weekly training volume would include 3 resistance training sessions, 3 team practice sessions, and a competitive match at the end of the week. However, participants were tested following a de-load period of 3 days to allow for peak performance in all tests. This study was approved by the University College Dublin Human Research Ethics Committee. Written informed consent was obtained from all participants before testing.
Testing took place over 2 days, separated by 1 week. On day 1, preliminary testing was performed to determine the optimal load in the HBJS to be used in further testing because this has been shown to be highly individual (1,17). On day 2, participants performed acceleration and jump testing at body weight and with their individual optimal load in the HBJS. Participants were asked to maintain and replicate their normal food and fluid intake before both testing dates and to refrain from alcohol consumption for at least 24 hours and caffeine for at least 3 hours. Before the commencement of testing, participants performed their normal daily battery of physical monitoring assessments, which included body-weight, a sit and reach test, groin adductor squeeze test, and hip internal and external rotation measures. Any participants who fell outside their established norms in these assessments were removed from testing. All testing took place between 9 AM and 11 AM to control for any diurnal variation and to reflect their normal training time.
To determine the individual optimal load in the HBJS, participants were tested at external loads equivalent to 10, 20, 30, and 40% of their box squat 1RM. Participants completed a standardized dynamic warm-up protocol, which consisted of leg swings (10 reps), bodyweight squats (10 reps), bodyweight alternate leg lunges (10 reps each leg), and body-weight single-leg stiff leg deadlifts (10 reps each leg). Loaded jumps as described by Swinton et al. (26) were performed on a force plate (HUR Labs, Tampere, Finland) in a randomized order, with each individual performing 2 trials across the range of loads. Force plate data were acquired at 1,200 Hz, The HUR Labs system was calibrated before each testing session. A built-in charge amplifier was used for data collection of the ground reaction force-time history of each jump condition. Ground reaction force data were passed through a fourth-order zero phase Butterworth low-pass digital filter with a 5-Hz cut-off frequency. Peak power output was automatically calculated by the HUR Labs software in accordance with the methods described by Sayer et al. (24), whereby peak power (W) = 60.7 × jump height (cm) + 45.3 × body mass (kg) − 2055. Participants began with the HB at arm's length, used a self-selected foot position, and were instructed to squat and immediately jump as high as possible. Participants descended to a half squat position for all conditions (approximately 60° of hip flexion, knee joint angle was not controlled for), which was visually monitored by the same researcher. Participants were required to repeat the trial if they did not achieve the required depth, as described elsewhere (26) or in the event of the bar accidently touching the floor. Participants performed 3 trials with 60-second rest between each trial and a 3-minute rest period between sets. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) for each loading condition was as follows: 0% CV range = 0.41–7.72, ICC = 0.96; 10% CV range = 0.49–7.92, ICC = 0.96; 20% CV range = 0.53–4.65, ICC = 0.98; 30% CV range = 0.11–10.72, ICC = 0.96; and 40% CV range = 0.53–8.04, ICC = 0.98. The load that produced the highest peak power output for each individual was selected as the optimal load to be used in further testing.
One week later, participants completed the standardized dynamic warm-up protocol described previously followed by a standardized warm-up for a speed session that consisted of “A” marches (2 × 10 m), “A” skipping (3 × 10 m), high knee running (2 × 5 m), high knee running into 10 m acceleration (2 × 5 m + 10 m), wall drill (2 × 12 reps), and 5 submaximal practice sprints over 20 m at 70–90% maximal intensity. Participants then performed a 20-m sprint and (3 × 10 m) on an indoor Mondo running track wearing regular running trainers. Speed times for both 10- and 20-m sprint were recorded with Brower timing gates (Brower TC-timing system; Brower Timing Systems, Draper, UT, USA), with participants starting from a standardized starting position 0.7 m behind the line to prevent any early triggering of the timing gates. In line with previously published literature (19), each sprint was performed with participants instructed to ensure maximal effort with a minimum of 3 efforts. A minimum of 3-minute rest between each effort was enforced to ensure full recovery. The fastest 20-m time and 10-m split from the best 20-m effort was used for analysis.
After speed testing, participants had a 2-hour break to allow for complete recovery before the commencement of jump testing. Participants repeated the standardized warm-up protocol described in the preliminary testing section. They then completed 3 unloaded CMJ trials on a force plate (HUR Labs) with data recorded at a frequency of 1,200 Hz. A built-in charge amplifier was used for data collection of the ground reaction force-time history of each jump condition. Ground reaction force data were passed through a fourth-order zero phase Butterworth low-pass digital filter with a 5-Hz cut-off frequency. They began with hands on hips, were instructed to squat to a self-selected depth, and immediately jump as high as possible. This protocol is similar to those used in previously published research (19,27). Jump height measured by flight time was the dependent variable used to quantify CMJ performance, which has been reported to have a high ICC (r = 0.983) (3). Three loaded HBJS trials were then performed as previously described with a load corresponding to the individuals' predetermined optimal load for peak power (from preliminary testing). Peak power normalized to the subject's body mass (i.e., relative peak power output) was the dependent variable used to quantify HBJS performance to account for the large variations in the body mass of the participants. For both the CMJs and the HBJS, subjects performed 3 trials with 60-second rest between each trial. A 3-minute rest period was used between the CMJ and HBJS sets. The peak performance of the 3 jumps for both the CMJs (height) and HBJS (relative peak power) was used for statistical analysis.
The relationship between HBJS relative peak power output, 10- and 20-m sprint time, and CMJ height was investigated using Pearson product-moment correlation coefficient. Standard multiple regression was used to assess the relationship between HBJS relative peak power output, CMJ height, and 10-m sprint time. A similar procedure was undertaken to investigate the relationship between HBJS relative peak power output, CMJ height, and 20-m sprint time. The strength of the correlations was evaluated according to the recommendations of Cohen (7) as follows: small r = 0.10–0.29; medium r = 0.30–0.49; large r = 0.50–1.0. Statistical analyses were conducted in IBM SPSS Statistics 20 (IBM Ireland Ltd, Dublin, Ireland). Statistical significance was set a priori at p ≤ 0.05.
Preliminary analyses were performed to ensure no violation of the assumptions of normality, linearity, and homoscedasticity. There was a strong, negative correlation between HBJS relative peak power output and 10-m sprint time (r = −0.70, n = 17, p < 0.01, coefficient of determination = 0.49), as well as 20-m sprint time (r = −0.75, n = 17, p < 0.01, coefficient of determination = 0.56) (Figures 1 and 2). There was a strong positive correlation between HBJS relative peak power output and CMJ height (r = 0.80, n = 17, p < 0.01, coefficient of determination = 0.64) (Figure 3).
Regarding the relationship between HBJS relative peak power output, CMJ height, and 10-m sprint time, preliminary analyses were undertaken to ensure no violation of the assumptions of normality, linearity, multicollinearity, and homoscedasticity. The full model was statistically significant explaining 46% of the variance in 10-m sprint time, F(2,16) = 7.93, p < 0.01, adjusted R2 = 0.46. The HBJS relative peak power output made the strongest contribution (beta = −0.44), followed by CMJ height (beta = −0.32).
Regarding the relationship between HBJS relative peak power output, CMJ height, and 20-m sprint time, preliminary analyses were undertaken to ensure no violation of the assumptions of normality, linearity, multicollinearity, and homoscedasticity. The full model was statistically significant explaining 59% of the variance in 20-m sprint time, F(2,16) = 12.65, p < 0.01, adjusted R2 = 0.59. Countermovement jump height made the strongest contribution (beta = −0.47), followed by HBJS relative peak power output (beta = −0.36).
Concerning the 2 undertaken multiple regression analyses, post hoc power analysis using G*Power (16) indicated that a power of 0.78 was achieved for 10-m sprint time, with a power of 0.95 being achieved for 20-m sprint time.
The results of the present study demonstrate a clear and significant relationship between relative peak power output in the HBJS and CMJ height and speed performance. Strong correlations were observed between HBJS relative peak power output and CMJ height. Similarly, HBJS relative peak power output was significantly negatively correlated with 10- and 20-m sprint time. As such, the primary hypotheses of the study were confirmed.
The strength and power levels of the participants in the current study compare favorably with those reported elsewhere in the literature. The box squat performance reported in this study is similar (2) or superior (1) to that reported in other investigations involving professional rugby union players. The jump squat peak power performance of the participants in this study is also superior to that reported elsewhere in 47 professional rugby union players (6). However, the study by Bevan et al. (6) involved the BBJS variation. When using the HBJS variation, Swinton et al. (26) reported peak power values below those of the current study. Therefore, the population in the current study is accurately described as elite within the context of similar studies involving rugby union players.
To the best of the researchers' knowledge, the present study is the only study that has used the HBJS variation and attempted to examine its' relationship with performance, expressed by CMJ height and 10- and 20-m sprint times. The strongest correlation was evident between HBJS relative peak power and CMJ height (r = 0.80). These findings are consistent with those reported elsewhere, using the BBJS variation (10,18,22). Hori et al. (18) have previously reported a similar positive correlation (r = 0.75) between peak power in a 40-kg traditional jump squat and CMJ height in a group of Australian rules football players. Strong, inverse correlations are also reported in the current study between relative peak power in the HBJS and acceleration times over 10 m (r = −0.70) and 20 m (r = −0.75). These findings are consistent with those reported elsewhere in the literature between peak power in the BBJS and speed performance (10,18,25). Cronin and Hansen (10) reported significant negative correlations between relative power in a 30-kg traditional jump squat and 5-m (r = −0.55), 10-m (r = −0.54), and 30-m (r = −0.43) speed times in a group of rugby league players. The results of this study confirm that the HBJS variation relates to athletic performance (CMJ and speed) to a similar degree as traditional BBJS methods.
Swinton et al. (26) speculated that the positioning of the load in the HBJS, when compared with a jump squat performed with a traditional barbell technique, allows the athlete to more closely replicate their unloaded jumping technique, therefore not adversely affecting the outcome of the jump. Swinton et al. (26) compared peak power outputs in the BBJS and HBJS variations with a range of loads. The highest peak power reported was in the HBJS condition with a 20% 1RM squat load. The peak power output in this condition was significantly higher than the unloaded condition. This is despite the fact that the unloaded condition was reported to produce higher peak power values than any of the BBJS loads in the same study. Similar findings have also been reported by Cormie et al. (9). Contradictory evidence exists as to what load maximizes peak power output in the BBJS (12).
The inclusion or exclusion of body mass in jump squat power calculations can significantly affect the load-power relationship (8). In all jump squat variations, the body mass must also be accelerated along with the external load (system mass) and therefore must be included in any power calculations (8). When power is reported in this manner, unloaded movements tend to optimize peak power output in comparison with the BBJS conditions (1,6,8,9,11). However, the findings of Swinton et al. (26) suggest that in the HBJS, peak power occurs in loaded conditions, which may be attributed to a more biomechanically advantageous positioning of the external load, when compared with the traditional BBJS (26). Swinton et al. (26) also postulated that the HBJS is a safer variation of the jump squat than the BBJS because of the positioning of the load at arm's length as opposed to loaded on the posterior aspect of the shoulders. These findings in addition to the findings of the current study have important implications for the strength and conditioning coach. The results of the current study demonstrate that the HBJS is related to performance to a similar degree as the BBJS, with previous evidence suggesting its superiority in the generation of peak power (26) because of the different load positioning of the exercise. Future research should examine the changes in performance following training interventions comparing both jump squat variations.
The strong correlation between performance in the HBJS and established measures of athletic performance, however, does not imply causation. The need for longitudinal training studies investigating the validity of the HBJS as a training tool for improving power output and linear speed and CMJ performance is evident. Training studies using traditional jump squat methods have reported an improvement in peak power output, which have been associated with positive changes in speed and vertical jump performance (21). Consequently, it is plausible that more significant improvements in athletic performance may occur following a period of training with this exercise because of the higher peak power output values associated with the HBJS. However, this hypothesis requires scientific validation through future research. Regardless, the potential of the HBJS in strength and conditioning programs is evident and establishing its association with athletic performance is an important step in validating it as a training tool.
In conclusion, the findings of the current study demonstrate a significant relationship between relative peak power in the HBJS and athletic performance. Significant correlations are reported between relative peak power output and CMJ height, 10-m and 20-m speed in a group of elite rugby union players. The findings of the study have important implications for strength and conditioning coaches and suggest that the HBJS relates significantly to athletic performance, which may support its inclusion in training programs in the preparation of elite athletes.
Based on the findings of this study, the HBJS is a valid speed-strength exercise that relates significantly to jump and acceleration performance in rugby union players. Strength and conditioning coaches should consider the inclusion of this exercise in the development of peak power output in addition to more traditional methods of light-load power training. Within a linear periodized plan, athletes could include this exercise variation in a power training block following a period of maximal strength development.
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