Lower extremity joint kinetic responses to external resistance variations

Area of Science:

• Biomechanics
• Motor Control
• Exercise Physiology

Background:

• Understanding how the body controls force production during resistance exercises is crucial for optimizing training and preventing injuries.
• The squat is a fundamental compound movement involving multiple joints, making it an ideal model for studying multi-joint biomechanics.

Purpose of the Study:

• To investigate whether net joint moment (NJM) work or average NJM scales proportionally with increased external resistance during the squat.
• To identify the primary joint contributors to force control during loaded squats.

Main Methods:

• Eighteen experienced subjects performed squats at 25%, 50%, 75%, and 100% of their 3-repetition maximum.
• Biomechanical data were collected using motion capture and force plates.
• Net joint moment work and average NJM at the hip, knee, and ankle were calculated using inverse dynamics and numerical integration.

Main Results:

• Neither NJM work nor average NJM increased proportionally with external resistance across all joints.
• The hip joint demonstrated a dominant, linear increase in contribution with external load and low variability.
• Knee and ankle joint contributions were less significant, non-linear, and highly variable, suggesting influence from factors beyond external load.

Conclusions:

• The control strategy for loaded squats is complex and not based on simple proportional scaling of joint moments.
• The hip joint plays a primary role in regulating force output during squats.
• Further research is needed to refine motor control theories for multi-joint movements.