Abdominal muscle recruitment and its effect on the activity level of the hip and posterior thigh muscles during therapeutic exercises of the hip joint.

Abdominal exercise has been advocated to improve the protection of the spine and neuromuscular efficiency of the limb movements. The purpose of this study was to examine the effect of enhanced contraction of internal oblique and transversus abdominis (IO/TrA) on the activity level of the hip and posterior thigh muscles during therapeutic hip exercises. Twenty healthy females were required to perform eight hip exercises under two conditions, natural versus enhanced IO/TrA contraction conditions. Muscle activity of gluteus maximus, gluteus medius, tensor fasciae latae and biceps femoris of the exercising leg was measured by surface electromyography during hip exercises, and expressed in percentage normalized to the maximal voluntary isometric contraction (%MVIC). The activity levels of the gluteal and posterior thigh muscles recorded under natural and enhanced IO/TrA conditions were compared. IO/TrA was found to have activated at the range of 2.7%-16.1% and 6.3%-24.1% of MVIC when hip exercises were executed under natural and enhanced conditions respectively. Enhanced IO/TrA contraction resulted in significantly greater activity in gluteus maximus, gluteus medius and bicep femoris at various phases of hip extension and clam exercises, single leg sit-to-stand and pelvic drop exercise (increased by 1.7-7.2% of MVIC). These findings indicate the presence of coactivation of the abdominal and hip muscles when performing the free active hip exercises. Further studies are recommended to investigate the efficacy of this muscle coactivation in improving the clinical outcome of therapeutic hip exercises.