Objectives: This study was conducted in order to determine the effect of feedback tools on activities of
the gluteus maximus (Gmax) and oblique abdominal muscles and the angle of pelvic rotation during
clam exercise (CE).
Design: Comparative study using repeated measures.
Setting: University laboratory.
Participants: Sixteen subjects with lower back pain.
Main outcome measures: Each subject performed the CE without feedback, the CE using a pressure
biofeedback unit (CE-PBU), and the CE with palpation and visual feedback (CE-PVF). Electromyographic
(EMG) activity and the angles of pelvic rotation were measured using surface EMG and a threedimensional
motion-analysis system, respectively. One-way repeated-measures ANOVA followed by
the Bonferroni post hoc test were used to compare the EMG activity in each muscle as well as the angle
of pelvic rotation during the CE, CE-PBU, and CE-PVF.
Results: The results of post-hoc testing showed a significantly reduced angle of pelvic rotation and
significantly more Gmax EMG activity during the CE-PVF compared with during the CE and CE-PBU.
Conclusion: These findings suggest that palpation and visual feedback is effective for activating the Gmax
and controlling pelvic rotation during the CE in subjects with lower back pain.