Pastorio, E. | bioRxiv Science

bioRxiv2025

Menstrual cycle phase alters corticospinal excitability and spike-timing-dependent plasticity in healthy females

The known fluctuations in ovarian hormone concentrations across the eumenorrheic menstrual cycle contribute to modulations in cortical excitability and inhibition. However, how such changes affect spike-timing-dependent plasticity (STDP) has not been systematically studied. This research aimed to determine the effect of the menstrual cycle on corticospinal excitability and STDP. Twelve eumenorrheic female participants (age: 25 {+/-} 5 years), visited the lab in three menstrual cycle phases: early follicular (EF), late follicular (LF), and mid-luteal (ML). Visits comprised of corticospinal excitability (motor evoked potential [MEP]/Mmax), short-intracortical inhibition (SICI), and intracortical facilitation (ICF) measures, recorded in the resting first dorsal interosseous. Followed by a paired associative stimulation (PAS) protocol, utilising ulnar nerve and transcranial magnetic stimulation (25 ms interstimulus interval) to elicit neuroplasticity. To assess the time course of STDP, measurements were repeated at 15 and 30-minutes post PAS. Corticospinal excitability (MEP/Mmax) was greater in the LF phase (p[≤]0.002) compared to EF and ML, with no phase effects observed for SICI or ICF (p[≥]0.112). PAS elicited an increase in MEP/Mmax across all phases at 15-minutes (112 {+/-} 5, 115 {+/-} 5, and 113 {+/-} 7% baseline, p[≤]0.010), whereas at 30-minutes only ML was facilitated (126 {+/-} 7% baseline, p=0.029). The present data demonstrates facilitatory STDP can be induced with PAS across the tested menstrual cycle phases, but responses are prolonged and potentiated in the ML phase. Additionally, increased corticospinal excitability in the LF phase is likely due to intrinsic changes within the descending tract, as no changes in intracortical neurotransmission were observed.

neuroscience↗

bioRxiv2025

Sex differences in durability following heavy intensity cycling exercise in trained athletes

The ability to withstand impairments in key physiological variables during prolonged exercise, known as durability, is emerging as an important factor in cycling performance. While females possess physiological characteristics that could confer enhanced durability relative to males, little is known about potential sex differences. 32 trained cyclists (16 males and 16 females) performed an incremental exercise test to exhaustion in visit 1. In visit 2 they performed 90 minutes of heavy intensity cycling (HVY) at 110% of gas exchange threshold (GET), followed by another incremental test. During HVY, pulmonary gas exchange ([V]O2 and [V]CO2) ventilation ([V]E), heart rate (HR), rating of perceived exertion (RPE), near-infrared spectroscopy and electromyography were recorded, and blood lactate (BLa) was collected. Before and after HVY, maximal voluntary contraction (MVIC), voluntary activation (VA) and potentiated twitches (100Hz, 10Hz, Qtw{middle dot}pot) of the knee extensors were assessed. Power at GET (-16{+/-}15% vs -2{+/-}13%) and respiratory compensation point (-13{+/-}10% vs -6{+/-}9%) decreased more in males than females (P[≤]0.049). All aspects of neuromuscular function decreased from pre to post (all P<0.001), without sex differences (P[≥]0.096). During HVY, HR, [V]O2 (%peak), relative energy expenditure increased more in males (P[≤]0.008), whereas respiratory exchange ratio decreased more in females (P=0.001). BLa was higher in males than females (P=0.030). Muscle oxygen extraction was lower (P=0.004) and tissue saturation index higher for females (P<0.001). The smaller reductions exhibited by females in submaximal thresholds, associated with lesser derangements to oxidative efficiency, highlight the need to consider sex-specific training prescription and pacing strategies for long duration events. Key PointsO_LIDurability, as measured by the reduction in incremental exercise test outcomes, is relatively unexplored in females compared to males, despite physiological sex differences that might confer a female advantage. C_LIO_LIAfter 90 minutes of heavy intensity cycling, males demonstrated greater reductions in the power outputs associated with gas exchange threshold and respiratory compensation point. C_LIO_LIThe maximal rate of oxygen consumption and incremental test peak power output decreased similarly in both sexes. C_LIO_LIThese changes are associated with greater carbohydrate metabolism and losses of efficiency in males, whereas no sex differences were observed in neuromuscular fatigue. C_LI

physiology↗