The dynamic warm-up and light exercise sets (e.g., 30, 50% 1RM HC) of the exercise that was to be performed that day (HC, JS, or HP) were performed before testing. For example, if the subjects were performing the JS during a testing session, they would perform sets of the JS at 30 and 50% 1RM HC as a part of their warm-up before performing testing repetitions. Subjects completed 3 maximal effort repetitions at each of their relative loads (30, 45, 65, and 80% of their 1RM HC) in a randomized order using the exercise of the day. Therefore, each testing session required the subject to perform 12 total repetitions. The same randomized order of relative loads was used during each testing session with the different exercises. In addition, the relative loads remained constant between each exercise. Due to the large number of repetitions, only 1 exercise (HC, JS, or HP) was tested per visit in a randomized order to prevent fatigue. Sixty seconds of rest was provided between each repetition (15), whereas 2 minutes were provided between each load. The bar was placed on the safety bars of a squat rack in between all repetitions to prevent fatigue. All repetitions of each exercise were performed on a portable Kistler Quattro Jump force platform (Type 9290AD; Kistler, Winterthur, Switzerland) interfaced with a laptop computer and were sampled at 500 Hz. The methodology of using a force platform only apparatus during weightlifting exercises is supported by Hori et al. (18,19). Finally, subjects were encouraged to complete each repetition with maximal effort.
Peak power output, PF, and PV of the center of mass of the lifter plus bar system were calculated from the vertical ground reaction forces of the HC, JS, and HP using a template created in Microsoft Excel (Microsoft Corporation, Redmond, VA, USA). The greatest PPO, PF, and PV values produced by each subject during the HC, JS, and HP at each load were used for comparison. Vertical ground reaction forces of the lifter plus bar system were measured directly with the force platform. The velocity and power output of the center of mass of the lifter plus bar system were calculated using a forward dynamics approach previously established (23).
All data are reported as the mean ± SD. A series of 3 (exercise) × 4 (load) repeated measures analysis of variance were used to compare the main effect differences of the PPO, PF, and PV produced between the HC, JS, and HP exercises and the various loads (30, 45, 65, 80% 1RM HC). When necessary, post hoc analyses were performed using the Bonferroni technique. All statistical analysis was performed using SPSS 20.1 (IBM, New York, NY, USA). For all statistical tests, the alpha value was set at 0.05. Statistical power was calculated between 0.87 and 1.00 for all measures. Effect sizes were calculated using Cohen's d and were interpreted using the scale developed by Hopkins (17), where effect sizes were considered trivial, small, moderate, large, very large, and nearly perfect when Cohen's d was 0.0, 0.2, 0.6, 1.2, 2.0, and 4.0, respectively. Finally, intraclass correlation coefficients, coefficients of variation, and 90% confidence interval ranges were calculated from the 3 separate repetitions of each exercise at each load and are displayed in Table 3. Ranges displayed indicate the values found at each load for each variable.
Exercise PPO main effect results are displayed in Figure 5. Significant differences in PPO occurred between the HC, JS, and HP exercises (p < 0.001). Post hoc analysis revealed a significantly greater PPO during the JS (5851.38 ± 1354.94 W) compared with both the HC (4123.61 ± 1135.32 W) (p < 0.001, d = 1.38) and HP (4737.08 ± 1196.36 W) (p < 0.001, d = 0.87). In addition, the PPO of the HP was significantly greater than the HC variation (p = 0.001, d = 0.53).
Exercise PF main effect results are displayed in Figure 6. Significant differences in PF were identified between the HC, JS, and HP exercises (p < 0.001). Post hoc analysis revealed a significantly greater PF during the JS (3593.99 ± 666.20 N) compared with both the HC (3267.19 ± 698.16 N) (p < 0.001, d = 0.48) and the HP (3337.02 ± 710.46 N) (p < 0.001, d = 0.37). However, no significant difference in PF existed between the HC and HP variations of the power clean (p = 0.309, d = 0.10).
Exercise PV main effect results are displayed in Figure 7. Significant differences in PV occurred between the HC, JS, and HP exercises (p < 0.001). Post hoc analysis revealed a significantly greater PV during the JS (2.15 ± 0.30 m·s−1) compared with both the HC (1.68 ± 0.26 m·s−1) (p < 0.001, d = 1.67) and HP (1.87 ± 0.26 m·s−1) (p < 0.001, d = 1.00). In addition, the PV of the HP was significantly greater than the HC variation (p < 0.001, d = 0.73).
Load PPO main effects are displayed in Figure 8. Significant main effects in PPO occurred between different loads during the HC, JS, and HP exercises (p < 0.001). The greatest PPO occurred at 45% 1RM HC (5124.82 ± 1538.26 W). This was followed in order by 30% (5045.81 ± 1705.51 W), 65% (4854.31 ± 1224.85 W), and 80% 1RM HC (4591.15 ± 1115.38 W). Post hoc analysis revealed that the PPO at 45% 1RM HC was significantly greater than PPO that occurred at 65% (p = 0.043, d = 0.19) and 80% 1RM HC (p = 0.004, d = 0.40). However, PPO at 45% 1RM HC was not significantly different from PPO at 30% 1RM HC (p = 1.000, d = 0.05). No other significant differences in PPO occurred between 30 and 65% 1RM HC (p = 0.663, d = 0.13), 30 and 80% 1RM HC (p = 0.105, d = 0.32), or 65 and 80% 1RM HC (p = 0.134, d = 0.22).
Load PF main effects are displayed in Figure 9. Significant differences in PF were observed between the different loads during the HC, JS, and HP exercises (p < 0.001). The load of 65% 1RM HC displayed the highest PF (3487.15 ± 710.75 N). This was followed in order by 80% (3485.96 ± 690.90 N), 45% (3409.71 ± 692.19 N), and finally 30% 1RM HC (3214.78 ± 701.99 N). Post hoc analysis revealed that the exercise load of 30% 1RM HC yielded significantly lower PF than 45% (p = 0.006, d = 0.28), 65% (p < 0.001, d = 0.39), and 80% 1RM HC (p = 0.003, d = 0.39). However, no significant differences in PF existed between 45 and 65% 1RM HC (p = 0.319, d = 0.11), 45 and 80% 1RM HC (p =0.427, d = 0.11), or 65 and 80% 1RM HC (p = 1.000, d = 0.00).
Load PV main effects are displayed in Figure 10. Significant main effects in PV occurred between different loads during the HC, JS, and HP exercises (p < 0.001). The greatest PV occurred at 30% 1RM HC (2.08 ± 0.40 m·s−1). This was followed in order of magnitude by 45% (2.01 ± 0.33 m·s−1), 65% (1.82 ± 0.21 m·s−1), and 80% 1RM HC (1.69 ± 0.21 m·s−1). Post hoc analysis revealed that PV at 30% 1RM HC was significantly greater than the PV produced at both 65% (p < 0.001, d = 0.81) and 80% 1RM HC (p < 0.001, d = 1.22). In addition, the PV produced at 45% 1RM HC was significantly greater than the PV produced at both 65% (p < 0.001, d = 0.69) and 80% 1RM HC (p < 0.001, d = 1.16). However, no significant difference in PV existed between 30 and 45% 1RM HC (p = 0.059, d = 0.19). Finally, 65% 1RM HC produced a significantly greater PV than 80% 1RM HC (p < 0.001, d = 0.62).
Exercise and Load Interaction
Significant interactions for PPO (p < 0.001), PF (p = 0.014), and PV (p < 0.001) were observed between the HC, JS, and HP exercises performed at different relative loads. The load at which the greatest PPO was produced, occurred at 65, 30, and 45% 1RM HC during the HC, JS, and HP, respectively (Figure 11). The exercise and load interactions for PF and PV are displayed in Figures 12 and 13, respectively. At every exercise load, the order of the greatest PPO, PF, and PV remained the same with the JS being the greatest followed in order by the HP and the HC. Given that the order of exercises remained the same (i.e., JS > HP > HC) in all variables measured throughout the loading spectrum within this study, the interaction seemed to be a result of the load. Thus, the greatest differences in PPO, PF, and PV between the exercises occurred at the lighter loads (30 and 45% 1RM HC), but these differences were less observable at the heavier loads (65 and 80% 1RM HC).
It is likely that the ideal stimulus for improving muscular power involves training in a way where maximal power production is produced during sports-specific movements (24). The main purpose of this study was to compare the power production of the HC, JS, and HP when performed at different loads relative to the 1RM HC of each subject. The main findings of this study were threefold. First, main effect differences in PPO existed between the HC, JS, and HP. The results of this study indicate that these differences are likely due to the PF and PV differences that existed between the exercises. For example, the JS produced significantly greater PF and PV than both the HC and HP, thus it makes sense that the JS produced the greatest PPO among the exercises examined. The secondary findings of this study included main effect differences in PPO, PF, and PV between the different exercise loads. Finally, there were interactions between the exercise (HC, JS, and HP) at specific loads for all of the variables examined in the current study. As hypothesized, the JS produced the greatest PPO. These values were followed in order by the HP and HC. Also hypothesized, the PPO for the HC occurred at 65% 1RM HC.
Previous research has documented that success in sports seems to be strongly related to the ability of athletes to produce high levels of muscular power (1,3,4,7,8,10,11,13–15,18,20,21,23–26,28–31). The HC, JS, and HP variations of the power clean are vertical pull exercises that are used to train lower body power. The nature of these exercises is similar in that they are all dependent on a powerful shrug of the shoulders and triple extension. However, our results indicate that the JS allowed for the greatest maximal power production by the subjects as compared with the HP and HC. In addition, the HP produced a greater PPO than the HC. It has been suggested that if athletes train using exercises that allow them to improve their muscular power, their overall athletic performance will also improve (23). Thus, it seems that the JS and HP exercises have the ability of producing high amounts of muscular power and should be considered as exercises that can be used to train lower body power.
Our results suggest that the largest contributing factor to the PPO of the JS and HP was the velocity of the lifter plus bar system during the movement. This seems logical because the JS and HP are more ballistic in nature than the HC. Our findings are supported by Newton et al. (29) who reported that the ballistic movement of a bench press throw, where the bar was released at the end of the range of motion, resulted in a greater velocity than a traditional bench press performed explosively. In the current study, part of the criterion for a successful repetition of the JS was that the subject's feet had to leave the platform during the movement as determined by observing the force-time curve immediately after the repetition. It is likely that this criterion required the subject's muscles to maintain higher force production throughout the entire range of motion, leading to a higher movement velocity (29). Therefore, the ability to produce a high velocity during the JS may be related to a greater need to focus on producing enough force and a fast enough velocity to leave the platform rather than focusing on catching the bar.
Although the HC is a highly beneficial exercise, it may be more time consuming to teach an athlete as compared with a power clean variation used to teach the HC (16). Previous authors recommend that practitioners should substitute less technical exercises to train lower body muscular power (1,20). By training with the JS and HP exercises, athletes with limited experience, injuries, or imperfect technique with the HC may still be able to effectively produce high levels of force, velocity, and power that seem to be important in sports performance. For example, if athletes struggle with HC technique, the results of this study indicate that it is possible to produce as much or greater lower body power by using the JS or HP as an alternative exercise. By implementing the JS or HP instead of the HC in this instance, there may be an increase in quality training time toward lower body muscular power, which will likely improve the athlete's overall performance in activities such as sprinting and jumping.
As previously mentioned, it has been suggested that strength and conditioning coaches should select exercises that allow their athletes to produce maximal power in the movement that is being trained (28). However, it is equally important for the practitioner to identify the loads that allow for maximal power production. Because many sports require high power output and explosiveness, it is preferred that athletes train at optimal loads so that the greatest stimulus for improved power output is provided (20,24,26,27,32). By training at the ideal load for each exercise, athletes will be able to optimally improve their muscular power and, furthermore, their overall performance (23).
The main effects of load in the present study indicated that the subjects produced the greatest PPO at 45% 1RM HC. What this means to practitioners is that, in general, the HC, JS, and HP produced the highest PPO at a lower load as compared with a higher load. This is to be expected considering that the PPO of the JS and HP occurred at the lower loads of 30 and 45% 1RM HC, respectively. Because the load main effect combines all the repetitions performed by the subjects within the study, it may not be the best indicator of what load optimizes PPO. Previous research indicates that it may be important to prioritize the use of the optimal load with the exercise that allows the athlete to produce a high PPO (20,24,26,27).
In the present study, the PPO for the HC was found at 65% 1RM HC. This finding is supported by previous research that has indicated that the optimal load for the HC and power clean exercises occurred at either 70% (4,23) or 80% 1RM (5,6,9,25). However, it should be noted that several studies observed that there was no significant difference between the optimal load and 60–80% 1RM (4) or 50–90% 1RM (9,23,25), which makes the optimal load found within this study comparable to previous research. The PPO for the JS occurred at 30% 1RM HC. To our knowledge, this is the first study to assess and compare the optimal load for the JS, making it difficult to compare our results with previous research. Finally, the PPO for the HP in the current study occurred at 45% 1RM HC, which falls within the range of 30–60% 1RM previously noted for the HP by Thomas et al. (32).
Analysis of the interaction between the exercises and loads revealed that the greatest PPO, PF, and PV at each load were produced by the JS. This was followed in order by the HP and HC at all loads. The greatest differences in PPO, PF, and PV between the exercises were at the lighter loads of 30 and 45% 1RM HC. However, the differences between exercises were smaller at the heavier loads of 65 and 80% 1RM HC. In general, as the load increased, the amount of force increased for each exercise. Although this remained true throughout the loading spectrum for the HC and HP, this was not the case for the JS. As the load exceeded 65% 1RM HC during the JS, the magnitude of the force decreased, although still greater than both the HC and HP. This is likely due to the breakdown of technique during repetitions at 80% 1RM HC. As the load continued to increase for each exercise, the velocity of the lifter plus bar system decreased. Based on the force-velocity relationship, it makes sense that because each subject was getting closer to their 1RM load, it was difficult for them to produce a high velocity. In regard to the power output of each exercise, it should be noted that the power output of the JS dropped about 1000 W over the loading spectrum, whereas the HC and HP only differed about 500 and 600 W, respectively. This finding highlights the need for practitioners to prescribe lighter loads for the JS exercise so that the athlete can effectively develop high levels of lower body muscular power.
A limitation of this study may have been the population selected. Athletic males with at least 2 years of previous experience with the HC were asked to participate in this study. That being said, no women, trained or untrained, were sought out as subjects. However, the subjects in the current study are part of a population that has been frequently examined throughout the literature and, therefore, this population may best allow for comparison with other studies. Finally, the current study used loads relative to the 1RM HC of each subject for each of the exercises examined. This was done to compare similar absolute loads in all exercises. The use of the array of loads (30–80%) was thought to be able to justify and identify differences of PF that may be apparent between exercises. Our results indicate that it is likely that the 1RM for the JS and HP are probably slightly higher than HC, so using a relative percentage of 1RM may have been another way of comparing loading; however, performing a 1RM test for the JS and HP in an athletic setting may not be practical.
The true optimal load for each exercise may be similar to those reported within this study, but it is recommended that future research may consider the use of smaller loading increments to better determine the optimal load for each exercise. Future research may consider the use of different populations, such as untrained men and both trained and untrained women, although comparing the HC, JS, and HP. To accurately determine how well each of these exercises trains lower body power, future research should consider analyzing the HC, JS, and HP using 3-dimensional motion analysis equipment to compare to what extent the hip, knee, and ankle joints extend during the second pull movement.
The results of this study may assist strength and conditioning practitioners in selecting exercises that maximize lower body power production during training, which may then enhance an athlete's performance in their respective sports. Because the JS and HP variations of the power clean exercise were superior to the HC in producing power, force, and velocity of the lifter plus bar system over the entire range of loads examined, it is suggested that strength and conditioning practitioners consider implementing the JS and HP exercises into their training regimens, especially for those who have trouble learning the HC. The JS and HP can be used as primary methods to improve lower body muscular power, but should also be used to complement exercises that are already being utilized to improve lower body muscular strength and power. To optimize power production with both the JS and HP exercises, practitioners should consider using loads at ∼30 and 45% of each athlete's 1RM HC, respectively.
This study was supported by a grant from the University of Wisconsin-La Crosse in La Crosse, Wisconsin. The authors would like to sincerely thank the subjects who participated in this research and made this project possible. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association. There is no conflict of interest. There are no professional relationships with companies or manufacturers who will benefit from the results of the present study for each author.
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Keywords:Copyright © 2014 by the National Strength & Conditioning Association.
hang clean; jump shrug; high pull; resistance training