Abstract
The decline in torque production of postural muscles during aging is considered as a key factor in the risk of falling. Recent works showed that the maximal torque of plantar flexor muscles (PF) was lower in older adults with recent fall history (OF) than in older non-fallers (ONF). The present study aimed to investigate the neural and mechanical factors associated with the lower maximal PF torque production in OF. Fifteen young adults (YA) (22 ± 4 years), 15 OF (84 ± 4 years) and 15 ONF (83 ± 4 years) were included in this study. Torque and electromyographic activity of soleus, gastrocnemii and tibialis anterior (TA coactivation) muscles were recorded during maximal voluntary contractions of the PF. Electrical nerve stimulation was used to assess the voluntary activation level (neural factor) during maximal plantar-flexion and the muscle contractile properties (mechanical factor). The results showed that the maximal PF torque was significantly lower (P<0.05) for OF (51 ± 12 Nm) than ONF (70 ± 15 Nm) and YA (119 ± 40 Nm). The voluntary activation level was lower (P<0.05) for OF (73 ± 18%) than ONF (82 ± 19%) and YA (90 ± 14%). A similar trend was observed for the maximal PF electromyographic activity. No difference in TA coactivation was reported among the three groups. While age affected the mechanical properties of ankle muscles (P<0.001), no difference was observed between ONF (13 ± 3 Nm) and OF (12 ± 3 Nm).
These results suggest that the alteration of muscle force production observed in OF could be mainly related to a deficit in muscle activation capability rather than reduced muscle contractile properties.