Sex-related Differences in Fractionated Reaction Time Are Not Related to Corticospinal Excitability and Inhibition.

To identify sex-related differences in fractionated reaction time (FRT) and assess the relationship between corticospinal excitability and inhibition and FRT of the first dorsal interosseous (FDI) muscle. Twenty-three healthy males (24.8 ± 2.8 years) and 23 healthy females (24.1 ± 3.6 years) completed 30 trials each of a simple and go/no-go (GNG) reaction time test. Participants abducted their index finger as fast as possible in response to a visual stimulus. FRT splits the reaction time response into the following segments: Premotor time (PMT; duration between stimulus onset and start of muscle activity), motor time (MT; duration between the onset of muscle activity and initiation of force production), and total reaction time (TRT; duration between stimulus onset and force production), were determined for each trial. Corticospinal excitability and inhibition of the FDI were assessed through the amplitude of the motor evoked potential normalized to Mmax (MEP/Mmax), and duration of the corticospinal silent period (CSP), respectively. Simple MT (p < 0.01), GNG MT (p < 0.01), and GNG TRT (p < 0.01) were significantly longer in females compared to males. Remaining FRT measures were not significantly different between sexes (p ≥ 0.06). Corticospinal excitability was similar between sexes (p = 0.21), while corticospinal inhibition was greater in males compared to females (p = 0.02). No significant correlations were present between FRT and corticospinal measures (r ≤ 0.33; p ≥ 0.13). Males begin to produce force sooner and have greater corticospinal inhibition. However, there was no relationship between FRT and corticospinal communication.