Purpose The aim of this study was to evaluate the muscle thickness of the rectus femoris during the application of squat exercises with functional electrical stimulation (FES), based on different ankle angles (toein 10°, toe 0°, toeout 10°). Methods Twentysix healthy participants were assessed. The squats were performed with three different ankle angles. They were divided into two groups: Group 1, squats at three ankle angles, and Group 2, squats with FES while applying three ankle angles. Results There were statistically significant differences in muscle thickness variation between group 1 and group 2 and before and after the ankle angle variations in each group (p<0.05). Group 1 and 2 showed statistically significant differences at both toein 10° and toeout 10°. Conclusion In both groups, the muscle thickness of the rectus femoris increased. This study suggests that performing squat exercises with a toeout 10°, along with FES, is recommended to enhance the effectiveness of the rectus femoris.