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

Abstract

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.

Keywords: Hip; Muscle strength; Muscle, skeletal; Postural balance; Rehabilitation.

Figure 1

Types of induced first-step protective responses following a waist perturbation. The arrow indicates the direction of pull. The grey leg is the stepping leg and black leg the stance leg. a) Demonstrates a medial recovery step while b) shows a cross-over recovery step.

Figure 2

Differences in the percentage (mean ± standard error) of Gluteus maximus and minimus/medius high density lean and IMAT from CT and the hip abductor torque (N.M) as tested with the biodex between groups (cross-steppers vs medial steppers). Significant differences were seen between the groups for both Gluteus min/med IMAT and hip abductor torque. *P<0.05.