Corticospinal Inhibition Is Greater In Males Than Females In An Upper And Lower Limb Muscle

Males and females differ in their neuroanatomy and may therefore differ in their neurophysiology. A previous study found greater corticospinal inhibition in males compared with females in the first dorsal interosseous (FDI). However, it is unclear if this sex-related difference in corticospinal inhibition is muscle specific. PURPOSE: The purpose of this study was to compare corticospinal excitability and inhibition between males and females in the FDI and tibialis anterior (TA) muscles. METHODS: Twenty healthy males (age: 23.2 ± 2.7 years; height: 179.7 ± 7.3 cm; weight: 77.1 ± 12.3 kg) and 20 healthy females (age: 22.7 ± 2.2 years; height: 163.8 ± 5.9 cm; weight: 61.6 ± 9.1 kg) completed two testing sessions, one for the FDI and one for the TA. The amplitude of the maximal M-wave (Mmax) was assessed as the maximal electrical response of the muscle to electrical stimulation of the ulnar nerve and deep fibular nerve. Participants then contracted their FDI or TA to 50% of their maximum force while single-pulse transcranial magnetic stimulation was applied to the area of the brain that controls the FDI or TA. Corticospinal excitability was measured through the amplitude of the motor evoked potential (MEP) and normalized to Mmax of each muscle. Corticospinal inhibition was assessed as the duration of the cortical silent period (CSP). Outcome measures were compared between muscles and sexes. RESULTS: There were no significant differences in MEP/Mmax amplitude between sexes (p = 0.64) or muscles (p = 0.23), and no significant interaction between sex and muscle (p = 0.40). CSP duration was significantly longer in males compared to females (p < 0.001) but was not different between muscles (p = 0.88), and there was no significant interaction between sex and muscle (p = 0.80). CONCLUSION: Healthy males had greater corticospinal inhibition than females in both the upper and lower limb, despite having similar levels of excitability. Natural Sciences and Engineering Research Council of Canada (RGPIN-2019-05127)