Role of Hip Abductor Muscle Composition and Torque in Protective Stepping for Lateral Balance Recovery in Older Adults

Objectives: To examine differences in hip abductor strength and composition between older adults who primarily use medial step versus cross step recovery strategies to lateral balance perturbations. Design: Cross-sectional. Setting: University research laboratory. Participants: Community-dwelling older adults (N=40) divided into medial steppers (n=14) and cross-steppers (n=26) based on the first step of balance recovery after a lateral balance perturbation. Interventions: Not applicable. Main Outcome Measures: Computed tomography scans to quantify lean tissue and intramuscular adipose tissue (IMAT) areas in the hip abductor, hip abductor isokinetic torque, and first step length. Results: Medial steppers took medial steps in 71.1% of trials versus 4.6% of trials with cross-steps. The cross-steppers when compared with medial steppers, had lower hip abductor IMAT (24.7 +/- 0.7% vs 29.9 +/- 2.8%; P <.05), greater abductor torque (63.3 +/- 3.6Nm vs 48.4 +/- 4.1Nm; P <.01), and greater normalized first step length (.75 +/-.03 vs.43 +/-.08; P <.001). There was no difference in hip abductor lean tissue between the groups (P >.05). Conclusions: Our findings suggest that older adults who initially use a medial step to recover lateral balance have lower hip abductor torque and may be less able to execute a biomechanically more stable cross-step. This may be related to increased IMAT levels. Assessments and interventions for enhancing balance and decreasing fall risk should take the role of the hip abductor into account. (C) 2016 by the American Congress of Rehabilitation Medicine