Lower Extremity Joint Kinetic Responses to External Resistance Variations

Abstract

The purpose of this investigation was to determine if increases in external resistance during a squat movement would be controlled by proportionally scaling the net joint moment work or average net joint moment (NJM) at the hip, knee, and ankle. Eighteen experienced subjects performed 3 sets of 3 repetitions each of a squat movement using resistances of 25, 50, 75, and 100% of their 3-repetition maximum, while instrumented for biomechanical analyses. Standard inverse dynamics techniques and numerical integration were used to calculate the NJM work and average NJM of each joint. A combination of single-subject and group mean statistical analyses indicated that the neither the NJM work nor average NJM increased proportionately in response to increases in external loading. Results suggest a complex control strategy in which the hip was the dominant contributor, increased linearly with the external load, and had low variability. The knee and ankle contributions were neither as great nor as linear, and were highly variable, suggesting that they were influenced by more than just the external load. The disproportionate response of each joint to varying external resistances suggests that controlling the force output of multijoint chains requires further study and modifications to existing motor control theories.

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

“…However, the joints respond differently with respect to power output where the knee and ankle joints reduced power output in accordance with the linear decrease in system power output as the external load increased, whereas the hip joint followed a quadratic trend. These differential responses in the lower-body joints as the external load increases have been reported by Flanagan and Salem (2008) in the back squat where the hip joint moment increased linearly with the increased external load whereas the knee joint moment decreased with increased load. The differences in the responses of the joint moments observed in this and the present study may be due to differences in the slower squat exercise compared to the more ballistic jump squat.…”

“…The differences in the responses of the joint moments observed in this and the present study may be due to differences in the slower squat exercise compared to the more ballistic jump squat. Unfortunately, Flanagan and Salem (2008) did not record joint power output during the squat movement. Kipp et al (2011) reported that power at hip was unaffected by the external load used during cleans performed with 65%, 75%, and 85% 1-RM.…”

The Influence of Load and Speed on Individuals' Movement Behavior

“…When presented with 2 tasks of the same pattern (e.g., lifting), but different demands (e.g., heavy vs. light load), some individuals may perform both with a very similar movement strategy; others, however, may adapt their movement behavior and exhibit varying degrees of task demand dependence. For example, Flanagan and Salem (11) found that among participants, a range of movement strategies were used to perform a squat, but interestingly, convergence in the net joint movements was noted as the load increased from 25 to 100% of the 3-repetition maximum.…”

Acute neuromuscular and metabolic responses to upper body strength, power, and hypertrophy protocols in resistance trained men

“…Exercises such as the back squat require more complex neural responses, considering the synergism of a higher number of active muscles [2,8] . Recent research indicates an increased involvement of the hip over the knee extensor muscles when heavier loads are lifted during squat exercise [7,9] . Therefore, the results observed in singlejoint muscles (i.e.…”

“…Additionally, previous studies have primarily manipulated multi-joint lower limb exercises, and different external loads among protocols, with no control of exercise cadence [7] . Probably, for these reasons, several studies have presented differences among RT protocols.…”