Neuromotor Characteristics Of Older Men With Sarcopenia

Abstract

Skeletal muscle mass increases over the first three decades of life, declines steadily through middle age, and more rapidly in older age. Sarcopenia describes a condition of significant loss of muscle mass in conjunction with reduced strength and function. While the changes in mass, strength and function across the lifespan are well-documented, little is known of the underlying neuromotor changes. PURPOSE: To examine the neuromotor mechanisms that underpin changes in muscles mass and function in older men with sarcopenia. METHODS: Twenty four older men (74.4 ±5.0yrs) were recruited for testing. Muscle and fat mass were determined by DXA (Norland XR-800, USA). Functional performance was assessed via isometric knee extension strength, timed-up-and-go (TUG), 5-times sit-to-stand (5TSTS), self-selected gait speed, and hand grip strength. Neuromotor function was assessed using electrical stimulation of the tibial nerve (Digitimer DS7AH, UK) and recording of EMG activity and torque during a graded plantar flexion contraction protocol. Measures included Level of Voluntary Activation (LoVA; 20%, 40%, 60% 80%, and 100% of MVC), resting and superimposed twitch (SIT), ankle torque, and EMG activity of the plantar and dorsi flexor muscles. RESULTS: Six older men were classified as sarcopenic based on DXA-derived measures of appendicular lean mass and height (<7.25kg/m2). Differences in LoVA and SIT were observed between older men and sarcopenic men at the 60% (LoVA: OM=85.5 ±5.5% SM=77.3 ±11.7%, p<0.05; SIT: OM=2.0 ±1.0% SM=3.6 ±2.8%, p<0.05) and 80% (LoVA: OM=95.8 ±2.4% SM=92.4 ±3.3%, p<0.05; SIT: OM=0.5 ±0.3% SM=1.2 ±0.8%, p<0.05) contraction intensities. Significant differences in knee extension strength were observed between older men and sarcopenic men (OM=512.2 ±125.2N SM=328.6 ±74.4N, p=0.03), however no other differences in functional performance measures were observed. CONCLUSIONS: These preliminary findings suggest that there are underlying neuromotor changes in men with sarcopenia, particularly during submaximal muscle contractions. Interestingly, men with sarcopenia were still able to maintain a similar level of functional ability compared to older healthy men. Future work will examine neuromotor characteristics in response to fatigue.