Age related changes of the motor excitabilities and central and peripheral muscle strength.

<bold>Introduction: </bold>The purpose was to investigate the age effects on central versus peripheral sources of strength, fatigue, and central neural excitabilities.<bold>Methods: </bold>42 healthy subjects were recruited as young group (23.73 ± 2.15 years; n = 26) and middle-aged group (57.25 ± 4.57 years; n = 16). Maximum voluntary contraction force (MVC), voluntary activation level (VA), and twitch force of quadriceps were evaluated to represent general, central, and peripheral strengths. Central and peripheral fatigue indexes were evaluated using femoral nerve electrical stimulation. Cortical excitabilities were evaluated using transcranial magnetic stimulation (TMS).<bold>Results: </bold>The middle-aged group had lower MVC and twitch force of quadriceps, but not VA, than young group. No between group differences were found in fatigue indexes. The cortical excitability in middle-aged group was different from young group in paired TMS with inter-stimulus interval of 7 ms.<bold>Conclusion: </bold>The age-related strength loss at early stage was primarily caused by peripheral muscular strength. The deviation of central neural excitability can be detected but the activation level was not impaired in middle-age adults. [ABSTRACT FROM AUTHOR]