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

Saeterbakken, Atle H.; Stien, Nicolay; Pedersen, Helene; Andersen, Vidar

February 2022 - Volume 36 - Issue 2 - p 304-309


Compared core muscle activity in a 3-RM performance of a  leg press, free-weight (FW) squat, and Smith machine squat regarding 1) surface electromyography (sEMG) and 2) the amplitude of sEMG during the switch over between the eccentric (lowering) and concentric (raising) phases.


sEMG activity was measured in the rectus abdominis (abs), external oblique (sides), and erector spinae (low back):

The leg press demonstrated only 17% stability compared to the FW squat @ 59% and Smith machine squat @ 42%. There was no significant statistical difference in stability between the FW squat and Smith machine squat.

There was no significant statistical difference between all three exercises during the switch from the eccentric and concentric phases regarding sEMG in the rectus abdominis.

A lower sEMG amplitude was observed in the external obliques and erector spinae in the leg press compared with the other two exercises.

The 3-RM loads in leg press were 54% and 47% greater than Smith machine squats and FW squats, respectively.


Lower 1) mean and 2) switch-over sEMG amplitude in the core muscles were observed in the core muscles when performing the leg press compared to both squat exercises. Greater 3-RM loads were used in the leg press compared with both squat exercises.


It’s a no brainer: because the leg press offered better overall stability, there was lesser involvement of the core muscles, and more resistance could therefore be used to better target the leg and hip muscles. The fact that the core was activated more in the FW squat and Smith machine squat was simply due to the less stable/standing position.

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