MUSCLE PERFORMANCE CHARACTERISTICS OF HIP AND ANKLE EXTENSORS AND THEIR RELATIONSHIP TO GAIT IN PERSONS AFTER HIP FRACTURE.

Abstract

Purpose/Hypothesis: Hip fracture adversely affects muscle performance and function. Muscle performance has been described as peak isometric force or isokinetic torque. However, the total force generated (impulse) during the initiation of contraction and the speed at which a person can generate the force (rate of force development (RFD)) may be as important as the peak values typically reported. The purpose of this report is to examine muscle performance characteristics (impulse, RFD, and peak torque) of the hip and ankle extensors and their relationship to walking speed, a measure of functional performance, in a sample of elders 6 months post hip fracture. Subjects: Twenty six patients (81 ± 6 yrs) who had completed all traditional, medicare-reimbursed rehabilitation were included in this study. They had an average of 4 comorbidities and were taking 5.5 medications. BMI was 27.4 ± 3.7 kg/m2. Materials/Methods: Measures included free and fast gait speed using the Gait Mat II; peak isometric torque; rate of force development; and impulse of the hip and ankle extensors using the Kincom and labview software. Results: Subjects produced significantly less isometric torque and did so more slowly on the involved side as compared to the non-fractured side. Comparing involved to uninvolved hip muscle performance characteristics, hip extensor impulse at 100 msec was 1.57 vs 1.83 N*m*sec and 4.44 vs 5.76 N*m*sec at 200 msec; hip extensor RFD at 100 msec was 199.1 vs 263.6 N*m*sec and 141.5 vs 200.7 N*m*sec at 200 msec; and hip extensor peak torque 62.5 vs 81.8 N*m. Comparing involved and uninvolved ankle muscle performance characteristics, ankle plantarflexion impulse at 100 msec was 0.96 vs 1.07 N*m*sec and 2.26 and 2.58 N*m*sec at 200 msec; ankle plantarflexion RFD at 100 msec was 62.8 vs 88.8 N*m/sec and 49.7 vs 63.6 N*m/sec at 200 msec; and ankle plantarflexion peak torque was 21.2 vs 24.3 N*m. Participants also walked more slowly in response to preferred (usual) speed (0.69 ± 0.18 m/sec) and fast speed commands (0.99 ± 0.27 m/sec) than age-matched peers. The relationships between muscle performance characteristics and gait speed were weak, at best(r values = 0.02–0.50). Conclusions: Muscle performance characteristics of the hip and ankle muscles have not been reported in persons after hip fracture. The results of this study suggest that the entire LE is impaired after traditional rehabilitation has stopped. Clinical Relevance: Exercise training may need to include rapid force production for the LE extensor muscle groups. It is not clear if gait speed is related to impulse or rate of force development in this small sample of elders post hip fracture.