Effect of very old age on anconeus motor unit loss and compensatory remodelling

INTRODUCTION: It is not known how the process of compensatory remodeling through collateral reinnervation continues into very old age (>80 years) or whether there is a limit to effective motor unit (MU) reinnervation. Therefore, we explore electrophysiological properties related to motor unit number estimates (MUNEs) in very old participants (79-90 years of age) compared with young controls (25-29 years of age). METHODS: Decomposition-enhanced spike-triggered averaging was used to collect surface and intramuscular electromyography information from the anconeus to derive a MUNE. RESULTS: Young participants had a MUNE of ∼38 and ∼25 at 30% and 50% root mean squared maximum voluntary contraction (RMSMVC ) with surface motor unit potentials (S-MUPs) of ∼145 μV and 236 μV, respectively. Older participants had a MUNE of ∼23 and ∼16 at 30% and 50% RMSMVC with S-MUPs of 168 μV and 232 μV, respectively. DISCUSSION: In this muscle, an age limit to successful remodeling through collateral reinnervation, to compensate for the presumed ongoing losses of MUs, may have been surpassed. Muscle Nerve 57: 659-663, 2018.