Core Muscle Activation in Three Lower Extremity Exercises With Different Stability Requirements

Area of Science:

• Exercise Physiology
• Biomechanics
• Sports Science

Background:

• Core muscle activation is crucial for stability and performance in resistance training.
• Understanding how different exercise variations affect core engagement is important for program design.
• Previous research has yielded mixed results on the impact of stability on core activation.

Purpose of the Study:

• To compare core muscle surface electromyography (sEMG) during 3-repetition maximum (3RM) testing.
• To assess sEMG amplitude in the turnover phase of lower extremity exercises.
• To investigate the influence of varying stability requirements on core muscle activation.

Main Methods:

• Nineteen resistance-trained women performed 3RM testing in randomized order for leg press, free-weight squats, and Smith machine squats.
• Electromyographic activity was measured in the rectus abdominis, external oblique, and erector spinae.
• sEMG amplitude was analyzed during 3RM and the transition phase between descending and ascending movements.

Main Results:

• Leg press exhibited significantly lower core muscle sEMG amplitude (17-59%) compared to free-weight and Smith machine squats.
• No significant differences in core sEMG were found between Smith machine and free-weight squats.
• Higher 3RM loads were achieved in leg press compared to both squat variations.

Conclusions:

• Lower stability exercises like the leg press elicit reduced core muscle activation but permit greater absolute loads.
• Squats, regardless of machine or free weight, engage the core more effectively than leg press.
• Increased stability demands (free weights vs. Smith machine) do not necessarily lead to greater core muscle sEMG amplitude.