Relative Neuroadaptive Effect of Resistance Training along the Descending Neuroaxis in Older Adults

Abstract

Age-related decline in voluntary force production represents one of the main contributors to the onset of physical disability in older adults and is argued to stem from adverse musculoskeletal alterations and changes along the descending neuroaxis. The neural contribution of the above is possibly indicated by disproportionate losses in voluntary activation (VA) compared to muscle mass. For young adults, resistance training (RT) induces muscular and neural adaptations over several levels of the central nervous system, contributing to increased physical performance. However, less is known about the relative neuroadaptive contribution of RT in older adults. The aim of this review was to outline the current state of the literature regarding where and to what extent neural adaptations occur along the descending neuroaxis in response to RT in older adults. We performed a literature search in PubMed, Google Scholar and Scopus. A total of 63 articles met the primary inclusion criteria and following quality analysis (PEDro) 23 articles were included. Overall, neuroadaptations in older adults seemingly favor top-down adaptations, where the preceding changes of neural drive from superior levels affect the neural output of lower levels, following RT. Moreover, older adults appear more predisposed to neural rather than morphological adaptations compared to young adults, a potentially important implication for the improved maintenance of neuromuscular function during aging.

Keywords: aging; neural adaptations; physical function; resistance training.

Figure 1

Flow-chart illustration of the literature search.

Figure 2

Potential sites of evaluations along the descending neuroaxis with corresponding techniques and parameters. Legend: TMS, Transcranial magnetic stimulation; V-wave, Volitional wave; H-wave, Hoffman wave; H-reflex, Hoffman reflex; EMG, Electromyography; EMS, Electrical muscle stimulation; SICI, Short-interval intracortical inhibition; LICI, Long-interval, Intracortical inhibition; RMT, Resting motor threshold; MEP, Motor-evoked potential; MUDR, Motor-unit discharge rate; M-max, Maximal elicited muscle amplitude.