The influence of strength training on muscle activation in elderly persons: a systematic review and meta-analysis.

Age-related muscle weakness is only partially related to muscle atrophy, due to neuromuscular changes including reduced voluntary muscle activation and antagonist muscle co-activation. The respective contribution of these mechanisms in exercise-induced strength gains at higher age is unclear. Here the literature was systematically reviewed for studies reporting exercise-induced effects on voluntary muscle activation and antagonist muscle co-activation in elderly persons. Seventeen relevant studies were identified, 4 investigated voluntary muscle activation, 8 antagonist muscle co-activation and 5 studies investigated both. Meta-analysis showed an exercise-induced improvement in voluntary activation in plantar flexors (weighted mean difference (WMD) +8.8%, p<0.001), and knee extensors (WMD +1.8%, p<0.001), with greater gains in activation capacity obtained in subjects with lower voluntary activation level prior to the onset of training. We found no significant overall effect of strength training on antagonist co-activation during ankle plantar flexion (WMD +0.6%, p=0.686) or knee extension (WMD -1.1%, p=0.699 for the RCT's and -1.8%, p=0.516 for the non-controlled trials). Based on our results we can conclude that there is evidence for exercise-induced increase in voluntary activation related to strength gains in the lower extremities in elderly persons. The results for exercise-induced effects on antagonist co-activation are inconsistent and more research is necessary to determine its contribution to strength gains following resistance training in elderly persons.