From Ergo Log
If you have a choice between doing a straightforward free-weight squat and using a Smith machine, go for the old-fashioned way of doing squats. According to a Canadian study – one in which the researchers attached electrodes to athletes’ muscles – doing a squat with free weights stimulates literally all muscle groups in the lower body better than the squat on the machine.
In theory there’s a lot to be said for doing squats on the Smith machine, admit the researchers who are based at the University of Saskatchewan. For one thing, the movement is more stable and therefore probably safer. In the Canadian study that has been published in the Journal of Strength and Conditioning Research, the increased stability had the effect that athletes were able to shift 13-25 kg more on the machine than with free weights.
But does that mean that your calf, thigh, stomach and lower back muscles work harder as well if you do your squats on a Smith machine? The researchers got six experienced power athletes to do a set of 8 reps on the machine and with free weights. The researchers attached electrodes to the test subjects’ muscles so that they could monitor the electrical activity.
In the figure below TA stands for tibialis anterior, the muscle that runs over your shin bone; the one that football players love to kick in their opponents. Gastroc stands for gastrocnemius, the Latin name for your calf muscle. VL stands for vastus lateralis and VM for vastus medialis. The vastus lateralis is situated on the side of your thigh, the medialis is the tear-shaped muscle on the inside of your leg, just above your knee.
All muscles worked harder when the test subjects did their squats with free weights, but only in the gastrocnemius and the vastus medialis was the difference statistically significant. These two muscles worked 34 and 49 percent harder respectively in the free-weight squat.
In the figure below BF stands for biceps femoris [one of your hamstring muscles], RA for rectus abdominis [your six-pack] and ES for erector spinae [your lower back muscle]. Once again, all muscles work harder during the free-weight squat than a machine squat.
For the biceps femoris the effect was statistically significant. This muscle worked 26 percent harder in the free squat than in the machine squat.
Taking all the muscles together, they worked 43 percent harder during the free squat.
The conclusion that the researchers draw is not surprising. “The free weight squat may be superior to the Smith machine squat for training the major muscle groups of the legs and possibly would result in greater strength development and hypertrophy of these muscle groups with long-term training.”
J Strength Cond Res. 2009 Dec;23(9):2588-91.