Biology subjects

Spillane, P.

Publications and source records attributed to Spillane, P..

5 recordsLinked to original sources

bioRxiv2026

Motor unit discharge properties are modestly influenced by menstrual cycle-related fluctuations in sex hormone concentrations

Concentrations of estradiol (E2) and progesterone (P4), the main female sex hormones, exhibit large fluctuations across the menstrual cycle. Due to their receptors throughout the central nervous system, both hormones have the potential to influence motor function by influencing ionotropic and metabotropic inputs to motor pools, which can be estimated through the neural codes extracted from motor unit discharge patterns. To address key methodological limitations in prior menstrual cycle research on motor output, we established the Motor Units and Sex Hormones (MUSH) collaboration. The objective of this multi-site investigation was to determine whether endogenous fluctuations in estradiol and progesterone influence human motor unit activity. We hypothesized that motor unit discharge rates and persistent inward current (PIC)-related contributions to discharge would be greatest during the late follicular phase, when estradiol concentrations were highest. Fifty females completed a comprehensive protocol involving menstrual cycle and ovulation tracking, serum hormone measurement, and high-density surface electromyographic recordings during isometric contractions to quantify motor unit activity in the early follicular, late follicular, and mid luteal phases. After exclusion of 10 females with either atypical hormone concentration profiles or insufficient motor unit yield, 40 remained in the final analysis. There were significant changes in several motor unit discharge variables between menstrual cycle phases and significant associations with hormone concentrations. Increased estradiol was associated with higher peak discharge rates and ascending discharge rate nonlinearity, while increased progesterone was associated with higher peak discharge rates, more discharge rate hysteresis and ascending discharge rate nonlinearity. Despite reaching statistical significance, the magnitudes of these effects (i.e., effect sizes) were small. Overall, these findings indicate that fluctuations in sex hormones influence motor unit behavior, but the effects are subtle, highlighting the need for well-powered and methodologically rigorous menstrual cycle research. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=151 SRC="FIGDIR/small/699975v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@2eb2c0org.highwire.dtl.DTLVardef@1d98359org.highwire.dtl.DTLVardef@13e772borg.highwire.dtl.DTLVardef@1bb27_HPS_FORMAT_FIGEXP M_FIG C_FIG KEY POINTSO_LIThere are small but detectable differences in motor unit discharge rates between menstrual cycle phases, which are predicted by within-participant fluctuations in estradiol and progesterone. C_LIO_LIDischarge rate patterns that provide estimates of neuromodulatory and inhibitory input suggest that estradiol and progesterone can influence spinal cord circuitry differently than has previously been documented in the brain, highlighting an understudied aspect of female neurophysiology. C_LIO_LIVariability in menstrual cycles and associate hormones makes large-scale, rigorous studies especially valuable in female neuromuscular research. C_LI

neuroscience↗

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↗

bioRxiv2025

Corticospinal, reticulospinal, and motoneuronal contributions to fatigability during a sustained contraction of the elbow flexors

Synaptic input to the motoneuron pool is altered during fatiguing muscle contractions. In humans, the corticospinal tract is often studied, with equivocal findings regarding its role in the reduction of force. To date, the involvement of the reticulospinal tract during states of fatigue has not been explored. Fourteen participants (28{+/-}6 years, nine males) visited the laboratory twice, first for a familiarisation, then an experimental trial. Participants completed a 5-min sustained elbow flexor contraction at an intensity eliciting 40% of the EMG recorded during a maximal isometric voluntary contraction (MVC). Before, during, and after the contraction, transcranial magnetic stimulation and electrical cervicomedullary stimulation were used to elicit motor evoked potentials (MEPs) and cervicomedullary evoked potentials during the silent period (SP-CMEPs) respectively, with CMEPs also being evoked in combination with a startling acoustic sound (CMEPcon). Electrical stimulation of the brachial plexus was used to evoke maximal compound action potentials of the elbow flexors (Mmax). The 5-min contraction induced a 53% loss of force (p<0.001), with no change in background EMG ([~]4% Mmax, p=0.293). Neither MEP amplitude (p=0.246) nor CMEPcon ratio (p=0.489) were altered during the contraction. Whereas CMEP and SP-CMEP amplitudes were reduced by [~]20 and 50%, respectively (p<0.001) and remained depressed post-task. The results suggest that neither corticospinal nor reticulospinal tract excitability was altered during a 5-min constant-EMG task at 40% maximal EMG. Instead, the aetiology of the neural contribution to fatigability appeared to be primarily related to the loss of motoneuron excitability.

neuroscience↗

bioRxiv2024

Sex differences in the cardiopulmonary and neuromuscular response to high-intensity interval exercise

Sex differences exist in the integrative response to exercise, however, these are typically researched during constant-load exercise. Interval exercise involves high-intensity efforts interspersed with recovery periods to repeatedly stress physiological systems, and it is currently unknown whether the response to this form of exercise differs between sexes. Ten males and ten females (age: 25{+/-}3 years) completed two experimental visits. First, an incremental treadmill exercise test was performed to obtain submaximal (lactate threshold) and maximal ([Formula] O2peak) data. Thereafter, visit two involved 4 x 3-min running intervals at 90% of the final incremental test velocity (v[Formula] O2peak), with 90 secs rest between intervals. Before exercise and after each interval, maximal voluntary contraction (MVC), quadriceps potentiated twitch (Qtw.pot), and voluntary activation (VA) were recorded. The rates of oxygen uptake ([Formula] O2), carbon dioxide production ([Formula] CO2) and ventilation ([Formula] E) were continuously recorded throughout. There was no sex difference in relative [Formula] O2peak (males: 47.2{+/-}6.0 vs. females: 44.4{+/-}5.8 ml.kg- 1.min-1, p=0.292). When expressed relative to peak values, there were no sex differences in the [Formula] O2 or [Formula] CO2 response to the interval task (p[≥]0.781). Females had greater [Formula] E, [Formula] E/[Formula] O2, and [Formula] E/[Formula] CO2 values during the first two intervals (p[≤]0.046). There were no sex differences in the reductions in MVC, Qtw.pot, and VA during the interval task (p[≥]0.150), however females had lesser reductions in Qtw.pot values post-exercise (-24{+/-}9 vs. -15{+/-}8%, p=0.044). Sex differences exist in the physiological response to interval exercise. Compared to males, females experienced greater hyperpnoea during the initial stages, and had lesser decreases in contractile function post-exercise.

physiology↗