The effects of load on system and lower-body joint kinetics during jump squats

Abstract

To investigate the effects of different loads on system and lower-body kinetics during jump squats, 12 resistance-trained men performed jumps under different loading conditions: 0%, 12%, 27%, 42%, 56%, 71%, and 85% of 1-repetition maximum (1-RM). System power output was calculated as the product of the vertical component of the ground reaction force and the vertical velocity of the bar during its ascent. Joint power output was calculated during bar ascent for the hip, knee, and ankle joints, and was also summed across the joints. System power output and joint power at knee and ankle joints were maximized at 0% 1-RM (p < 0.001) and followed the linear trends (p < 0.001) caused by power output decreasing as the load increased. Power output at the hip was maximized at 42% 1-RM (p = 0.016) and followed a quadratic trend (p = 0.030). Summed joint power could be predicted from system power (p < 0.05), while system power could predict power at the knee and ankle joints under some of the loading conditions. Power at the hip could not be predicted from system power. System power during loaded jumps reflects the power at the knee and ankle, while power at the hip does not correspond to system power.

Weightlifting Pulling Derivatives: Rationale for Implementation and Application

“…As mentioned above, practitioners should be cautious when prescribing ''optimal loads,'' as previous research indicates that loads for peak power development may be specific for the lifter-plus-bar system [2, 27, 64, 69, 99-103, 117, 119] or barbell [109][110][111], or altered to specific joints [112][113][114][115]. Furthermore, the ''optimal load'' could change with trained state or accumulated fatigue, as determined by relative strength level [47].…”

“…Taken collectively, these studies and coaching reviews indicate that the optimal load for peak power production of the lifter-plus-bar system occurs between 70 and 80 % 1RM for the clean, snatch, power clean, and hang power clean exercises, and between 90 and 95 % 1RM for weightlifting pulling derivatives. However, practitioners should be aware that optimal loads beyond the lifter-plusbar system exist, as several studies indicated that the optimal load for peak power production may also be specific to the barbell [109][110][111] or can be altered to specific joints [112][113][114][115]; thus, the optimal load may change based on the biomechanical approach being used to assess power.…”

“…In addition, high force movements may improve peak power and the load range of power development [52,143]. Finally, during the strength-power phase, the primary goal is the development of peak power, and therefore a range of loads should be prescribed, as previous research indicates that peak power may be specific to the lifter-plus-bar system [2, 27, 64, 69, 99-103, 117, 119] or barbell [109][110][111], or can be altered to specific joints [112][113][114][115]. Within this phase, a practitioner may consider implementing exercises such as the jump shrug because of its highly ballistic nature at loads of B45 % 1RM hang power clean to maximize peak velocity and peak power [64,69].…”

Deconstructing the power resistance relationship for squats: A joint‐level analysis

“…However, these velocities and forces only represent the overall net effect of all muscles that are acting in a coordinated fashion through multiple joints to effect the movement. Although total system power reflects the sum total of joint powers well for squats (Moir et al., ), maximal power for coordinated multi‐joint dynamic tasks such as leg extension is likely constrained by coordination rather than simultaneously maximizing power output of all contributing muscles and at all lower limb joints (Wakeling et al., ). Therefore, the resistance at which system power is maximized may not reflect the resistance at which each lower limb joint power output or individual muscle power output is maximized.…”

Relative Intensity Influences the Degree of Correspondence of Jump Squats and Push Jerks to Countermovement Jumps

“…Thus, when considering the internal (joint) kinetics, the PJ is more similar in those athletes who are knee dominant jumpers. Taking into regard, the continuum of general to specific exercises for sports performance, for those athletes who adopted more hip dominant strategies the PJ may be a more general exercise and movements considered to produce more hip moment, such as jump squats (29), could instead be used as a more specific exercise for these athletes. Further research in various movements may add further insight into this matter.…”