Influence of hip flexion angle on strength and gluteal muscle activities in the clinical pilates clamshell exercise.

The study aimed to investigate the presence of directional preference using the Clinical Pilates method of clamshell exercise among relatively healthy young adults, and the influence of hip flexion angles on maximum isometric strength (handheld dynamometer) and muscle activities (electromyography). The clamshell assessment involves testing in varying angles of hip flexion (0°, 30°, 60° and 90°) and 21 participants were tested. Directional preferences in the transverse and anteroposterior axes of movements were present among the participants. Gluteus medius activation was highest in the non-problem side across all hip flexion angles. In contrast, the problem side showed dysfunction of the gluteus medius, especially at the 60° hip flexion angle, 0.89 unit (ratio of maximal voluntary isometric contraction) reduction per 1 N force exerted, 95% CI -1.69 to -0.09, p = 0.031. Comparison against the non-problem side found gluteus medius activity lower on the problem side, mean difference (SD) was 26.2 (56.1), p = 0.045. Therefore, directional preference is not limited to people with injuries and can exist in healthy individuals or people who have recovered from injuries. The gluteus medius was identified to be dysfunctional on the problem side and Clinical Pilates clamshell assessment is potentially useful in assessing for motor coordination impairment.