The results of the current study suggest that performing the HPC and JS can be used to match the mechanical demands of the CMJ. In addition, and unsurprisingly, increasing the external load lifted during the HPC and JS effectively overloads the lower extremity extensor muscles beyond the levels required to execute a maximal effort CMJ. Although load-dependent increases in NJM are well documented across resistance training and weightlifting exercises, none have made joint kinetic comparisons between these tasks and the CMJ (Bryanton et al., 2012; Kipp et al., 2011; 2012; 2018). The results of the current study showed that the peak lower-extremity extensor NJM during the execution of the HPC at 30% 1-RM were equal to those of the CMJ. Furthermore, an increase in the external load of the HPC to 50% of 1-RM or above resulted in all NJM of the lower extremity during the HPC being greater than during the CMJ. For the JS, the NJM of the knee and ankle were greater than the NJM of the CMJ regardless of the external load. In addition, the hip NJM during the JS exceeded the hip NJM of the CMJ once the JS load exceeded 50% of 1-RM. Although previous research showed that increases in external loads lead to increases in the magnitude of lower extremity joint work performed during the execution of the HPC and JS (Kipp et al. 2018), no previous studies have made direct statistical comparisons between the mechanical demands of the lower extremity extensor muscles during CMJ and the HPC or JS. While Cushion et al. (2016) reported NJM for the CMJ, push jerk, and jump squat, these authors did not compare joint kinetics between these exercises. However, brief examination of their data suggests similar load-dependent increases in NJM that lead to the knee and ankle NJM exceeding those during the CMJ (Cushion et al. 2016). It therefore appears that performing these weightlifting derivatives at 50% of 1-RM or greater increases the NJM demands enough to overload the lower extremity extensor muscles beyond the mechanical requirements of the CMJ. Notably, however, the mechanical outputs at the knee and ankle joint during the JS already exceed the mechanical demand of the CMJ, even if the JS is performed with only 30% of 1-RM. Although these findings may justify the use of weightlifting derivatives, such as the HPC and JS, in efforts to improve CMJ performance, an intervention study would be required to test this assertion. The correlation analyses showed several significant positive correlations between the NJM of the CMJ and weightlifting derivatives. More specifically, one the major finding of this analysis was that at 70% of 1-RM all the NJM of both weightlifting derivatives were highly correlated with their respective counterparts during the CMJ. In addition, at 50% of 1-RM all NJM of the JS were also highly correlated with those of the CMJ. The fact that the NJM correlation coefficients between the CMJ and the two weightlifting derivatives differed across loads indicated that the mechanical similarity changed as the external load increased. Cushion et al. (2016) similarly reported that the NJM correlations between CMJ and the push jerk and jump squat changed across load. It is perhaps not surprising that the correlations between CMJ and JS NJM were more consistent across a broader range of loads and joints because the JS is executed with an emphasis on jumping as high as possible with the barbell whereas the HPC is executed with an emphasis on catching the barbell in a front rack, semi-squat position (Suchomel et al. 2017). Even though the execution of weightlifting derivatives is often described as “jumping with weights,” the current results suggest that this comparison becomes more valid when the HPC is performed with relatively high loads. In contrast, it appears that the comparison between the CMJ and JS NJM are valid across all loads. Depending on this joint-load combination, the JS therefore appears to provide an effective lower extremity overload stimulus. This finding, however, should be considered in light of previous research that indicated that the JS may be best implemented with lighter loads, while the HPC may be best implemented with moderate to heavy loads (Kawamori et al., 2005; Kilduff et al., 2007; Kipp et al., 2018; Suchomel et al., 2017). Analyses of the joint- and load-based interactions between the NJM of the HPC and JS suggest that differences were most apparent at the knee and ankle joint, and at 30% and 50% of 1-RM. More specifically, the joint-averaged NJM at 30% and 50% were greater for the JS than the HPC, while at 70% there were no differences. In addition, the difference in load-averaged NJM between the HPC and JS existed only at the knee and ankle joints, but not for the hip joint. Furthermore, only the hip and ankle exercise-averaged NJM joints exhibited load-dependent behavior across the range of 1-RM conditions. Collectively, these results thus indicate that the JS is associated with greater mechanical demands of the knee and ankle joints, especially at lighter loads. These results agree with previous research that showed greater knee and ankle joint power during the JS than the HPC, especially at 30% and 50% of 1-RM (Kipp et al. 2018). Given that load-dependent differences between the HPC and JS disappear at 70%, it could be surmised that the two weightlifting derivatives become more mechanically similar, perhaps because it is possible to execute the HPC and JS with several different movement strategies and still complete each task at lower loads. The results from this study should be interpreted in light of several limitations. First, the focus of the current manuscript was on investigating the mechanical similarity between CMJ and weightlifting derivatives. The findings therefore do not hold much direct insight into performance for the sport of weightlifting. Second, the current study used only a cross-sectional research design, which precludes making ultimate conclusions about which weightlifting derivative would lead to the greatest increase in CMJ performance if used as part of a longitudinal research study. For example, limited longitudinal evidence suggests that training programs that implement weightlifting derivatives that either include or exclude the catch phase have similar positive effects on CMJ performance (Comfort and Suchomel, 2018). Similarly, one other study indicated that training with either loaded hexagonal barbell jumps or high pulls performed from the hang position produce similar adaptations in CMJ performance after 10 weeks of training (Oranchuk et al., 2019). Lastly, the small sample size of the current study likely increased the uncertainty in the calculation of the correlation coefficient, which led to the large range of confidence intervals. Given the spread in the confidence intervals it is difficult to reliably distinguish between the strengths of the correlation coefficients aside from either significant or not, and the results from the correlation analyses should therefore be interpreted accordingly. |