Neuromuscular Transmission Stability In Very Old World-class Masters Athletes

Abstract

Natural adult aging is associated with the gradual loss of functioning motor units (MUs), a process that accelerates in the 8th decade of life. It has been shown in only a few studies that endurance trained masters athletes (MA) between 60 and 95 years of age had more MUs than age-matched controls, but both groups had lower numbers than young adults. However, it is not known how physical activity may affect the fidelity of neuromuscular transmission in old age. PURPOSE: To explore electrophysiologic factors that reflect MU stability in world-class masters athletes, 75 years of age and older, in comparison with age-matched controls. METHODS: A maximal compound muscle action potential (CMAP) was recorded from the tibialis anterior muscle (TA), in 5 healthy controls (aged 75 to 95 years) with a comparable group of 6 MA of the same age range. Decomposition-enhanced spike-triggered averaging was used to analyze surface and intramuscular EMG from the TA during a series of submaximal (20% MVC) voluntary dorsiflexion contractions in order to derive a motor unit number estimation (MUNE). Near fibre (NF) motor unit potential (MUP) analysis was performed to provide a detailed assessment of neuromuscular status. Near fibre jiggle is a parameter that measures the variability of consecutive isolated MUs. RESULTS: Compared with controls, the MA were 39% stronger and had greater MUNEs (51 vs. 73, respectively). Furthermore, preliminary results indicate that controls had a significantly higher jiggle value than the MA (66.9% vs. 46.3%, respectively). CONCLUSIONS: Greater MU stability in MA may be due to the high-intensity or volume of training and indicative of more stable MUs (lower degree of MU remodeling), which could reflect the physical activity-associated relative preservation of MUs compared with controls. Supported by NSERC.