INFLUENCE OF AGE ON NEUROMUSCULAR CONTROL OF THE KNEE.

Abstract

Purpose/Hypothesis: An increased incidence of injury has made neuro-muscular control of the knee joint a focus of attention in motor control research. The central nervous system (CNS) controls the knee against unpredictable perturbations that occur during movement. Age associated changes in the musculoskeletal, neuromuscular and sensory systems compromise the ability of the elderly to respond effectively to a perturbation, thereby placing the older population at a higher risk of injury. Weight bearing exercises have been primarily used to re-educate neuromuscular control of the knee following pathology. Limited information is available on the strategies used by the elderly to control the knee during dynamic activities. This study examined the effect of age on the neuromuscular control of the knee by examining accuracy of performance, muscle synergies and long latency reflexes (LLR) during a functional weight bearing exercise. We hypothesized that the elderly would show greater impairment in neuro-muscular control than the young. Number of Subjects: Ten young and ten elderly subjects performed a single leg squat exercise (SLS) while tracking a sinusoidal target with knee motion at different levels of resistances (4%, 8% and 12% body weight). Materials/Methods: Subjects first performed a set of learning trials to gain proficiency with the task. Later, they performed the SLSs with random perturbations (drop in resistance level to 0% BW) during the knee flexion phase. A split plot repeated measures ANOVA was used to assess between and within group differences in movement accuracy, synergistic activation patterns (EMG), and long latency reflexes. Results: The elderly group 1) had a 50% greater absolute error in tracking the target angle when compared to the younger group (p < 0.05); 2) showed a 60% greater activation of the quadriceps and hamstrings at all levels of resistances as compared to the younger group (p < 0.05); and showed 15% greater LLR for the quadriceps and biceps femoris when compared to the younger group (p < 0.05). Conclusions: These results indicate that the elderly recruit higher percentages of MVC and have greater error when performing the SLS weight bearing exercise. Clinical Relevance: Age associated changes of the sensorimotor system necessitates greater muscle activity to help stabilize the knee in the elderly. These findings provide important clinical implications when developing rehabilitation programs for the young and elderly.