Gluteus medius strength, endurance, and co-activation in the development of low back pain during prolonged standing

This study measured gluteus medius (GM) strength and endurance before and after a 2 h prolonged standing task in previously asymptomatic individuals, to compare between individuals who did and did not report pain in the low back. Twenty-four participants without a history of low back pain stood in a constrained area for 2 h. Before and after the standing protocol, participant's maximal hip abduction strength (N)and side-bridge endurance (seconds and GM myoelectric fatigue) were measured. Continuous surface EMG was collected from GM during the 2-h protocol for analysis of bilateral co-activation. Pain in the low back was rated every 15 min with a visual analog scale (VAS). Seventeen of 24 (71%) previously asymptomatic participants developed pain in the low back during the standing protocol. These participants had lower side-bridge endurance (p=.002), and higher gluteus medius (GM) co-activation (p=.002) compared to participants who did not develop pain in the low back. Hip abduction strength decreased for both groups following prolonged standing, with no between groups' difference. Lower side-bridge endurance and hip abduction strength were significantly associated with higher GM co-activation (adjusted r(2) = .34), but not pain levels. Side-bridge endurance and GM co-activation, but not hip abduction strength, may have utility in identifying participants likely to develop pain in the low back during prolonged standing. The best training program for increasing GM endurance is unclear. (C) 2010 Elsevier B.V. All rights reserved.