Design

A randomized, controlled study was used to examine the effects of three squatting exercises with different stability requirements by assessing 10 repetitions maximum (10RM), maximal voluntary isometric contraction (MVIC), RFD, countermovement jump (CMJ), muscle thickness and EMG activity. The three exercises, performed with either a low, medium or high degree of instability, involved squats performed using a Smith machine (low), squats with free weights (medium) or squats with free weights while standing on two wobble boards (high). All participants were tested three times: prior to the intervention (pre-test), after 3 weeks (post-familiarization), and after 10 weeks (7 weeks post-familiarization) of training (Fig 1). During the first 3 weeks (familiarization period), all participants trained each of the three squat exercises. After the week 3-test, the participants were randomized into either a control group or groups that performed training twice per week for 7 weeks with either a low, medium or high degree of instability. Participants in the Control group refrained from all resistance training targeting the legs between week 3-test and week 10 test (post-test).