For those of you who are still using the Smith Machine to Squat, here is another reason why you should set yourself "free".
A recent study published in the Journal of Strength and Conditioning Research, examined the electromyographic activity (EMG) of various muscles during the squat exercise when performed using the Smith machine as well as using free weights. This was performed as a follow up to a 2005 study by Anderson and Behm that demonstrated higher EMG activity of the quadriceps muscles during the Smith Machine squat.
The major difference between this and that of its predecessor was that a weight equal to an 8RM for EACH exercise (to facilitate relative intensity) was utilized in comparison to a fixed, absolute weight for both exercises used by Anderson and Behm.
EMG activity was collected for the following musculature:
A relatively low "N" was used: 3 men, 3 women. All were active in sports and familiar with the use of both free weights and the Smith machine.
The average absolute EMG activity for the free weight squat was:
Interestingly, no significant differences in EMG activity of the trunk musculature were found between the two exercises. I will keep my opinions to myself on this, especially when only 6 subjects were used.
Additionally, I was both surprised and disappointed the authors failed to include the gluteal musculature within this study since hip extension is one major component of the squat exercise.
These findings likely represent a increased stabilizing role of the above musculature for the hip, knee and ankle during free weight squats.