Quadriceps effort during squat exercise depends on hip extensor muscle strategy

Area of Science:

• Biomechanics
• Exercise Physiology
• Sports Science

Background:

• The interplay between hip extensors (gluteus maximus and hamstrings) and knee extensors (quadriceps) significantly impacts biomechanical demands during exercises like the barbell squat.
• Understanding the relative contribution of different hip extensor muscles is crucial for optimizing performance and preventing injury.

Purpose of the Study:

• To investigate how different hip extensor activation strategies influence quadriceps relative muscular effort (RME) during the barbell squat.
• To compare the biomechanical demands on the quadriceps under varying hamstring co-contraction assumptions.

Main Methods:

• Development of inverse dynamics-based torque-driven musculoskeletal models to simulate hamstring co-contraction during barbell squats.
• Utilizing 3D motion analysis and force platform data to calculate net joint moments.
• Modeling two hamstring co-contraction scenarios: (1) equivalent gluteus maximus and hamstring activation (Model 1), and (2) preferential gluteus maximus activation (Model 2).

Main Results:

• Quadriceps RME was significantly higher in both modeled scenarios (Model 1 and Model 2) compared to analyses without considering hamstring co-contraction, particularly at loads between 50-90% of one repetition maximum.
• Model 1 (equivalent activation) resulted in a peak quadriceps RME of 120% ± 36%, while Model 2 (preferential gluteus maximus activation) showed a peak RME of 87% ± 28%.
• The findings suggest that barbell squats are biomechanically feasible primarily when a strategy prioritizing gluteus maximus activation over hamstring activation is employed.

Conclusions:

• The hip extensor strategy, specifically the balance between gluteus maximus and hamstring activation, critically affects quadriceps effort during barbell squats.
• A preferential gluteus maximus activation strategy is essential for maintaining feasible quadriceps relative muscular effort during heavy barbell squats.
• Developing balanced strength in both the gluteus maximus and quadriceps muscles is vital for optimizing performance and load-bearing capacity in the squat exercise.