Muscle & Nerve · Jan 10, 2018
Sarcolemmal excitability changes in normal human aging
By Lee JHF, Boland-Freitas R, Ng K
INTRODUCTION: The exact mechanisms underlying the loss of skeletal muscle bulk and power with normal human aging are not well established. Recording of muscle velocity recovery cycles (MVRCs) is an in-vivo neurophysiologic technique we employed to assess the impact of age on sarcolemmal excitability. METHODS: MVRC recordings were obtained from tibialis anterior (n = 74) and rectus femoris (n = 32) muscles in 74 healthy subjects (18-84 years, median age 35 years, interquartile range 29-55 years). RESULTS: Increasing age was linearly associated with longer muscle relative refractory period (MRRP) and reduced early supernormality (ESN) in both tibialis anterior (MRRP: r² = 0.38, P < 0.001; ESN: r² = 0.33, P < 0.001) and rectus femoris (MRRP: r² = 0.30, P = 0.002; ESN: r² = 0.19, P = 0.01) muscles. DISCUSSION: The results are consistent with progressive depolarization of the resting sarcolemmal potential with normal aging. This may be an important mechanism in explaining age-related muscle decline. Muscle Nerve 57: 981-988, 2018.