The Journal of Orthopedic and Sports Physical Therapy published an article in the September 2015 issue about the differences between completed a resisted upright side step verses a resisted squat side step.  I found this article to be very interesting because I use these two exercises in my practice when trying to help patients who have hip abduction weakness and present with a hip drop or a trunk lean while walking.  Here is the synopsis of the article and hopefully it helps you achieve your goals.

The researchers studied the muscle activation of the gluteus maximus, gluteus medius, and tensor fascia lata (TFL).  The subjects were given a theraband and wrapped it around their ankles with about 110% tension in the band.  Pt participant was then instructed to start with their feet 12 inches apart and side step to about 24 inches apart  and back to 12 inches apart for 8 steps in each direction.  The two posture used were upright standing without flexion in the hips and knees and the subject’s preferred squatting position.

The researchers found that the greatest muscle activations of the gluteus maximus, gluteus medius, and TFL were found in the stance limb compared to the moving limb, the muscle activation of the TFL was less and the gluteus muslces was greater in the squatting position compared to the upright position, and their was more hip abduction excursion in the stance limb compared to the moving limb.

So when completing these exercise, it is important to consider which muscles you want to focus on and the functional goal that you would like to improve upon.

Berry JW, Lee TS, Foley HD, Lewis CL. Resisted side stepping: the effect of posture on hip abductor muscle activation. Phys Ther. September 2015; 45(9):675-682.