Impact of decline-board squat exercises and knee joint angles on the muscle activity of the lower limbs

[Purpose] This study aims to investigate how squat exercises on a decline board and howthe knee joint angles affect the muscle activity of the lower limbs. [Subjects] Thesubjects were 26 normal adults. [Methods] A Tumble Forms wedge device was used as thedecline board, and the knee joint angles were measured with a goniometer. To examine themuscle activity of the biceps femoris, rectus femoris, gastrocnemius lateralis, andtibialis anterior of the lower limbs, a comparison analysis with electromyography wasconducted. [Results] The muscle activity of the biceps femoris, rectus femoris,gastrocnemius lateralis, and tibialis anterior increased with increased knee joint angles,both for squat exercises on the decline board and on a flat floor. When the knee jointangle was 45°, 60°, and 90°, the muscle activity of the rectus femoris was significantlyhigher and that of the tibialis anterior was significantly lower during squat exercises onthe decline board than on the flat floor. When the knee joint angle was 90°, the muscleactivity of the gastrocnemius lateralis was significantly lower. [Conclusion] Squatexercises on a decline board are an effective intervention to increase the muscle activityof the rectus femoris with increased knee joint angles.Key words: Decline board, Squat exercise, Range of motion