The purpose of this study was to compare muscle activity and kinetics during the back squat and overhead squat performed at three relative intensities (60, 75 and 90% 3RM). Fourteen subjects (age: 26 ± 7 yrs, height: 182.5 ± 13.5 cm, body mass: 90.5 ± 17.5 kg) performed each exercise using a within-subjects crossover design. In addition, a selection of trunk isolation exercises were included to provide additional comparisons. Squats were performed on a force platform with electromyographic (EMG) activity of the anterior deltoid (AD), rectus abdominis (RA), external oblique (EO), erector spinae (ES), gluteus maximus (GM), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (GA) recorded throughout. The overhead squat demonstrated significantly greater (p<0.05) activity in the anterior trunk muscles (RA and EO) during the eccentric phase. However, the magnitudes of the differences were relatively small (∼ 2 to 7%). In contrast, the back squat displayed significantly greater (p<0.05) activity in the posterior aspect of the trunk (ES) and all lower-body muscles during the concentric phase. Kinetic comparisons revealed that significantly greater peak force (p<0.05) was developed during the back squat. EMG comparisons between the trunk isolation exercises and squat variations demonstrated substantially greater anterior trunk activity during the isolation exercises, whereas the highest activity in the posterior aspect of the trunk was obtained during the squats (p<0.05). The results of the study do not support the hypothesis that the overhead squat provides a substantially greater stimulus for developing the trunk musculature compared with the back squat.