Motor unit number estimates in world‐class masters athletes: is 80 the new 60?

Abstract

Despite age‐related loss of functioning motor units (MU), masters athletes (MA) in their 7th decade of life retained more MUs than recreationally active controls in the tibialis anterior (TA). It is unknown whether MAs beyond the 7th decade would show similar results. The purpose was to estimate the number of functioning MUs (MUNE) in world‐class, older male (n=4; 80 ± 5 y) and female (n=4; 80 ± 8 y) MAs ranging from 75 to 93 y. A maximal compound muscle action potential (CMAP) was recorded from the TA. Decomposition‐enhanced spike‐triggered averaging was used to analyze surface and intramuscular EMG from the TA during voluntary dorsiflexion contractions in order to derive a MUNE. For both sexes, CMAP was ~43% greater than previously reported in age‐matched normative data in males (6.7 ± 0.9 vs 4.7 ± 1.0 mV) (McNeil et al 2005), which may suggest a maintenance of excitable muscle mass in MAs. Mean surface MU potential (SMUP) size was similar between female MAs (64.3 ± 8.1 μV ) and normative data (78.2 ± 19.3 μV ), whereas male MAs had greater SMUP size than either group (138.0 ± 58.5 μV ). The resultant MUNE for female and male MAs was 100 ± 9 and 55 ± 24 MUs, respectively (p<0.05), with females but not males being higher than age norms. These preliminary results may indicate a sex‐specific protection of MUs in elite MAs >; 75 y of age, where MAs of both sexes may better maintain excitable muscle mass with aging.Supported by: CIHR (MOP 84408 to T.T.)