Biology subjects

Piasecki, M.

Publications and source records attributed to Piasecki, M..

13 recordsLinked to original sources

bioRxiv2026

The heterogeneity of age-related muscle atrophy of lower limb muscles

Age-related skeletal muscle atrophy differs between upper and lower body muscles and may also differ between lower limb muscles, but these muscle-specific patterns remain poorly characterised. We acquired axial 3T magnetic resonance images from sex-balanced samples of thirty young (24+/-4 years) and thirty older adults (73+/-4 years). Muscle volume of seventeen lower limb muscles/compartments was quantified using manual segmentation and expressed as absolute volume, relative to body mass, and as a percentage of total muscle volume. Absolute muscle volume was lower in older adults in 13 out of 17 muscles compared to young, with substantial heterogeneity in the effect sizes (d=0.01-3.36). Age group * muscle interaction contrasts revealed muscle-specific age-related differences in volume. Three of the quadriceps muscles demonstrated greater age-related atrophy compared to several other muscles (e.g. vastus lateralis differing from 14 of the other 16 muscles; d[≥]1.54). Conversely, the anterior and deep posterior compartments of the shank and biceps femoris short head showed significantly smaller age-related atrophy than several other muscles. These interaction effects were exacerbated when expressed in relative terms. Consequently, three of four shank compartments, gluteus maximus and adductor magnus represented a greater proportion of total muscle volume in older adults, whereas the vastus lateralis, vastus intermedius, rectus femoris, semitendinosus, gracilis, and iliopsoas contributed a smaller proportion in older adults. These findings highlight the variability in age-related leg muscle atrophy in a large mixed sex cohort, resulting in a redistribution of muscle volume in the lower limb.

physiology↗

bioRxiv2026

Acute caffeine ingestion differentially alters motor unit behaviour during submaximal and fatiguing contractions

Background: Caffeine is widely used as an ergogenic aid, yet its effect on neuromuscular function remains heterogeneous across exercise conditions. Although caffeine is known to enhance central nervous system excitability through adenosine receptor antagonism, the extent to which these effects modify spinal motor output remains unclear. Therefore, the present study aimed to characterise acute caffeine-induced alterations in neuromuscular properties during submaximal and sustained fatiguing contractions of the knee extensors. Methods: Seventeen healthy adults completed a randomised, placebo-controlled crossover study (3 mg/kg caffeine). Circulating serum caffeine concentrations were periodically quantified, while motor unit (MU) discharge behaviour, and delta F were derived from high-density surface electromyography. Statistical significance was set at p = 0.05. Results: No intervention effects were observed for MVC, force steadiness, or time to task failure (all p > 0.05). During graded contractions, vastus lateralis MU discharge rate was higher under caffeine (p < 0.001), and discharge variability was lower (p = 0.016). Recruitment and derecruitment thresholds were significantly greater under caffeine at 50% MVC (both p < 0.012), whereas paired MU analyses of delta F was unchanged (p = 0.083). During sustained contractions, caffeine altered fatigue-related trajectories of both MU discharge and discharge variability (intervention * phase interaction, p < 0.011). Conclusions: Acute caffeine ingestion alters motor unit behaviour without enhancing maximal force or fatigue resistance. These effects vary with contraction intensity and fatigue state but are not accompanied by a detectable change in discharge rate hysteresis in the vastus lateralis.

physiology↗

bioRxiv2026

Reduction in Ia afferent input via ischaemia alters motor unit discharge characteristics and estimates of persistent inward currents

Persistent inward currents (PICs) govern motoneuron output and are influenced by diffuse neuromodulation and local inhibition. When large diameter afferent feedback is lost, as in some neurological conditions, PICs might additionally amplify and prolong synaptic inputs. Here, we examined whether reducing Ia afferent transmission via ischaemic nerve block alters PIC contribution to tibialis anterior (TA) motor unit (MU) discharge. Across two experiments 12 adults (5 female) performed triangular-shaped isometric dorsiflexion to 30% (Experiments 1 and 2) and 50% (Experiment 2) maximum voluntary force (MVF) at baseline, after a 20-minute rest (control), and during occlusion after inducing an ischaemic nerve block, confirmed by abolition of the soleus H-reflex. TA myoelectrical activity measured during contractions was decomposed into MU spike trains, and from smoothed MU discharges, discharge rate hysteresis ({Delta}F) and ascending non-linearity (brace height) were quantified. Results from Experiment 1 involving contractions matched to absolute force levels revealed increased peak discharge rate, {Delta}F, and brace height post-occlusion. However, {Delta}F normalised to maximal theoretical hysteresis did not change across time points. In Experiment 2, where MVF was reassessed at each timepoint and contractions were matched to relative force, peak discharge rate, normalised {Delta}F and brace height increased post-occlusion compared to pre-, across both contraction intensities. {Delta}F only increased post-occlusion at 50% MVF, with no changes at 30% MVF. These results show that ischaemic block of large-diameter axons, likely reducing reciprocal inhibition, increases PIC contribution to discharge rate modulation, highlighting the role of Ia afferent input in shaping motoneuron output in humans.

neuroscience↗

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

Task Complexity and Limb Dominance Modulate the Effects of Ageing on Neuromuscular Function

BackgroundNeuromuscular function is critical for independence in ageing, yet asymmetries between dominant and non-dominant limbs, arising from central or peripheral mechanisms, are not well understood. This study examined age- and limb-related differences and motor unit (MU) firing behaviour of the vastus lateralis under tasks of varying difficulty. MethodsTwenty-one young (22 {+/-} 4 years; 15M, 6F) and seventeen older adults (74 {+/-} 5 years; 12M, 5F) performed constant and variable force unilateral isometric knee extensions. In both limbs, high-density surface electromyography signals were decomposed into MU spike trains. Force control and MU firing properties were analysed using multilevel mixed-effects regression models. ResultsOlder adults showed reduced maximal muscle strength (p<0.001) and increased force tracking error (p=0.008), MU firing rate (MUFR) was significantly lower in older adults during constant contractions (p = 0.001) and trended toward lower during variable contractions (p=0.061). MUFR variability showed a significant Leg x AgeGroup interaction (p<0.001); older adults had greater variability in non-dominant legs, while younger adults showed the opposite. With variable force contractions in both age groups, MUFR was higher during ascending segments with greater variability during descending segments. ConclusionNeuromuscular ageing involves asymmetric adaptations rather than a uniform decline, with leg dominance effects become more pronounced under variable force modulation. Task difficulty amplifies these asymmetries, underscoring the need to consider limb-specific neural control in age-related motor assessments.

physiology↗

bioRxiv2025

Bilateral neuromuscular adaptation to acute unilateral resistance exercise in healthy older adults

IntroductionResistance exercise (RE) enhances functionality in older adults and has proven effective as a means of cross-education in scenarios of unilateral disuse. However, the extent to which older adults demonstrate cross-limb transfer at the motor unit (MU) level following a single bout of unilateral RE is unclear. MethodsThirteen healthy older adults (74.9 {+/-} 4.8 years; 5 females) underwent bilateral neuromuscular assessments pre- and post- a single bout of unilateral RE consisting of 3-4 sets of 8-12 repetitions of leg extension of the dominant (exercise) leg, at 75% of 1 repetition maximum, performed to failure. Maximum voluntary contraction (MVC) and force steadiness (FS) were measured. Central and peripheral features of individual MU were recorded using high-density surface electromyography and intramuscular electromyography (HDs/iEMG), during contractions normalised to 25% MVC. ResultsFollowing unilateral RE, MVC reduced in exercise (-14.8%, p < 0.001) and control (-6.9%, p = 0.003) legs, with reduced FS performance in the exercise leg compared to the control (p = 0.002). MU firing rate increased during contractions normalised to 25% baseline MVC in the exercised leg (p < 0.05), with no adaptation in the control leg (p > 0.05). All iEMG recorded measures of MU potentials remained unchanged in both legs (all p > 0.05). ConclusionAcute unilateral RE leads to bilateral MVC reduction in older males and females, demonstrating the cross-limb transfer effect. However, adaptation of MU features was only apparent in the exercised limb, and mechanisms underlying the force decline in the non- exercised limb remain uncertain.

physiology↗

bioRxiv2024

Theta-gamma transcranial alternating current stimulation enhances motor skill acquisition in healthy young and older adults

Theta-gamma transcranial alternating current stimulation (TG tACS) over primary motor cortex (M1) can improve motor skill acquisition in young adults, but the effect on older adults is unknown. This study investigated the effects of TG tACS on motor skill acquisition and M1 excitability in 18 young and 18 older adults. High-definition TG tACS (6 Hz theta, 75 Hz gamma) or sham tACS was applied over right M1 for 20 minutes during a ballistic left-thumb abduction motor training task performed in two experimental sessions. Motor skill acquisition was quantified as changes in movement acceleration during and up to 60 minutes after training. Transcranial magnetic stimulation (TMS) was used to assess changes in M1 excitability with motor-evoked potentials (MEP) and short-interval intracortical inhibition (SICI) before and after training. We found that TG tACS increased motor skill acquisition compared with sham tACS in young and older adults (P < 0.001), with greater effects for young adults (P = 0.01). The improved motor performance with TG tACS lasted at least 60 minutes after training in both age groups. Motor training was accompanied by greater MEP amplitudes with TG tACS compared to sham tACS in young and older adults (P < 0.001), but SICI did not vary between tACS sessions (P = 0.40). These findings indicate that TG tACS over M1 improves motor skill acquisition and alters training-induced changes in M1 excitability in healthy young and older adults. TG tACS may therefore be beneficial to alleviate motor deficits in the ageing population. Key Points SummaryO_LITheta-gamma transcranial alternating current stimulation (TG tACS) can improve motor function in healthy young adults, but the effect on older adults is unknown. C_LIO_LIWe found that TG tACS improved motor skill acquisition with long-lasting effects in healthy young and older adults, but effects were stronger in young adults. C_LIO_LITranscranial magnetic stimulation showed that TG tACS altered the training-induced changes in motor cortex excitability, but there was no effect of TG tACS on intracortical inhibition in young or older adults. C_LIO_LIOur data suggest that TG tACS represents a promising approach to improve motor skill acquisition throughout the lifespan, and may be beneficial in older patient populations that experience motor or cognitive deficits. C_LI

neuroscience↗

bioRxiv2023

Sex disparities in age-related neuromuscular decline: unveiling female susceptibility from early to late elderly

BackgroundFemales typically have a longer lifespan than males which is not matched by an improved healthspan, with older females having higher rates of frailty, characteristic of a sex specific degradation of the neuromuscular system. Several motor unit (MU) characteristics show sex-specific behaviour during mid-level contractions in healthy younger people, highlighting a potential influence of hormonal differences that may be augmented in older age. The purpose of this study was to investigate sex differences in physical performance and MU features of the aged human vastus lateralis (VL) from early to late elderly. MethodsThis study included 21 healthy older males (mean {+/-} SD, range: 67.2 {+/-} 7.6, 56 - 81 yrs) and 17 healthy older females (69.5 {+/-} 5.2, 60 - 78 yrs). Intramuscular electromyography data were collected from VL during standardised submaximal sustained contractions. Muscle size and physical performance characteristics were also measured. Multiple mixed-effects linear regression models with age considered were conducted and statistical significance was accepted when p<0.05. ResultsWhen compared to males, early to late elderly females had smaller cross-sectional area of VL (p<0.001), lower knee extensor torque (p<0.001) and poorer force steadiness (p=0.036), as well as higher MU firing rate (FR) (p=0.025) and greater MU FR variability (p=0.031). With progression from early to late elderly, both sexes showed decreased functional capacity at a similar rate. ConclusionFunctional deterioration occurs to a similar extent in both sexes from early to late elderly. However, throughout the majority of the elderly period males demonstrate a greater muscle size, strength, and functional performance. Older females have greater MUFR variability and worse force steadiness than older males. These findings help to address the lack of MU data in older females, and suggest earlier interventions are needed in older females to prevent functional deterioration and reduce the health-sex paradox within ageing humans.

physiology↗

bioRxiv2023

Menstrual cycle associated alteration of vastus lateralis motor unit function

Estrogen and progesterone are the primary female sex hormones and have net excitatory and inhibitory effects, respectively, on neuronal function. Fluctuating concentrations across the menstrual cycle has led to several lines of research in relation to neuromuscular function, yet evidence from animal and cell culture models have yet to be demonstrated in human motor units (MU) coupled with quantification of circulating hormones. Intramuscular electromyography (iEMG) was applied to record MU potentials (MUP) and corresponding MUP trains (MUPT) from the vastus lateralis of eumenorrheic females during the early follicular, ovulation and mid luteal phases of the menstrual cycle, alongside assessments of neuromuscular performance. Multi-level regression models were applied to explore effects of time and of contraction level. Statistical significance was accepted as p<0.05. Knee extensor maximum voluntary contraction (MVC), jump power, force steadiness, and balance did not differ across the menstrual phases (all p>0.4). Firing rate of low threshold MU (10% MVC) was reduced during phases of high progesterone ({beta}=-0.82Hz, p<0.001), with no difference in MUPs analysed from 25% MVC contractions. MUPs were more complex during ovulation and mid luteal phase (p<0.03), with no change in neuromuscular junction transmission instability (p>0.3). Assessments of neuromuscular performance did not differ across the menstrual cycle. The suppression of low threshold MU firing rate during periods of increased progesterone may suggest a potential inhibitory effect and an alteration of recruitment strategy, however this had no discernible effect on performance. These findings highlight contraction level dependent modulation of VL MU function over the eumenorrheic cycle.

physiology↗

bioRxiv2023

Reduced motoneuron excitability and common synaptic inputs of the aged human vastus lateralis

Although muscle atrophy may partially account for age-related strength decline, it is further influenced by alterations of neural input to muscle. Persistent inward currents and the level of common synaptic inputs to motoneurons influence neuromuscular function. However, these have not yet been described in aged human quadriceps. High density surface electromyography (HDsEMG) signals were collected from the vastus lateralis of 15 young (mean{+/-}SD, 23 {+/-} 5 y) and 15 older (67 {+/-} 9 y) men during submaximal sustained and 20-s ramped contractions. HDsEMG signals were decomposed to identify individual motor unit discharges, from which delta F and intramuscular coherence were estimated. Older participants produced significantly lower knee extensor torque (p<0.001) and poorer force tracking ability (p<0.001) than young. Older participants also had lower delta F (p=0.001) and coherence estimates in the alpha frequency band (p<0.001) during ramp contractions when compared to young. Persistent inward currents and common synaptic inputs are lower in the vastus lateralis of older males when compared to young. These data highlight altered neural input to the clinically and functionally important quadriceps, further underpinning age-related loss of function which may occur independently of the loss of muscle mass. Key PointsO_LIThe age-related loss of muscle mass is exceeded by the loss of function, which is influenced by structural and functional alterations of the nervous system. C_LIO_LIMotoneuronal persistent inward currents and common synaptic inputs play an important role in the activation of motor units and subsequent force generation and control ability. C_LIO_LIHere we show reduced estimates of persistent inward currents and lower common synaptic inputs to older vastus lateralis, potentially contributing to observed lower strength and poorer force tracking. C_LIO_LIThese findings highlight decrements of the aged human motor system, accompanied by muscle atrophy in functionally relevant muscle groups, which should be considered in the application of interventions targeting aged human muscle. C_LI

physiology↗

bioRxiv2022

Motor unit dysregulation following 15 days of unilateral lower limb immobilisation

Disuse atrophy, caused by situations of unloading such as limb immobilisation, causes a rapid yet diverging reduction in skeletal muscle function compared to muscle mass. While mechanistic insight into the loss of mass is well studied, deterioration of muscle function with a focus towards the neural input to muscle remains underexplored. This study aimed to determine the role of motor unit adaptation in disuse-induced neuromuscular deficits. Ten young, healthy male volunteers underwent 15 days of unilateral lower limb immobilisation with intramuscular EMG (iEMG) recorded from the vastus lateralis during knee extensor contractions normalised to maximal voluntary contraction (MVC) pre and post disuse. Muscle cross-sectional area was determined by ultrasound. Individual MUs were sampled and analysed for changes in MU discharge and MU potential (MUP) characteristics. Vastus lateralis (VL) CSA was reduced by approximately 15% which was exceeded by a two-fold decrease of 31% in muscle strength in the immobilised limb, with no change in either parameter in the non-immobilised VL. Parameters of MUP size were largely reduced with immobilisation, while neuromuscular junction (NMJ) transmission instability increased, and MU firing rate decreased at several contraction levels. All adaptations were observed in the immobilised limb only. These findings highlight impaired neural input following immobilisation reflected by suppressed MU discharge rate and instability of transmission at the NMJ which may underpin the disproportionate reductions of strength relative to muscle size. Key pointsO_LIMuscle mass and function decline rapidly in situations of disuse such as bed rest and limb immobilisation. C_LIO_LIThe reduction in muscle function commonly exceeds that of muscle mass, which may be associated with the dysregulation of neural input to the muscle. C_LIO_LIWe have used intramuscular electromyography to sample individual motor unit and near fibre potentials from the vastus lateralis following 15 days of unilateral limb immobilisation. Following disuse, the disproportionate loss of muscle strength when compared to size was associated with suppressed motor unit firing rate and increased markers of neuromuscular junction transmission instability. C_LIO_LIThese central and peripheral motor unit adaptations were observed at multiple contraction levels and in the immobilised limb only. Our findings demonstrate neural dysregulation as a key component of functional loss following muscle disuse in humans. C_LI

physiology↗

bioRxiv2022

Training induced improvements in knee extensor force accuracy are associated with reduced vastus lateralis motor unit firing variability

BackgroundMuscle force output during sustained submaximal isometric contractions fluctuates around an average value and is known to be influenced by variation in motor unit (MU) firing rates. MU firing rate variability seemingly reduces following exercise training interventions, however, much less is known with respect to peripheral MU properties. We therefore investigated whether targeted force accuracy training could lead to improved muscle functional capacity and control, in addition to determining any alterations of individual MU features. MethodsTen healthy participants (7 females, 3 males, 27{+/-}6 years, 170{+/-}8 cm, 69{+/-}16kg) underwent a 4-week supervised, unilateral, force accuracy training intervention. The coefficient of variation for force (FORCECoV) and sinusoidal wave force tracking accuracy (FORCESinu) were determined at 25% maximal voluntary contraction (MVC) pre- and post-training. Intramuscular electromyography was utilised to record individual MU potentials from the vastus lateralis (VL) muscles at 25% MVC during sustained contractions, pre- and post-training. ResultsKnee extensor muscle strength remained unchanged following training, with no improvements in unilateral leg-balance. FORCECoV and FORCESinu significantly improved in only the trained knee extensors by ~13% (p=0.01) and ~30% (p<0.0001) respectively. MU firing rate variability significantly reduced in the trained VL by ~16% (n=8; p=0.001), with no further alterations to MU firing rate or neuromuscular junction transmission instability. ConclusionOur results suggest muscle force control and tracking accuracy is a trainable characteristic in the knee extensors, which is likely explained by the reduction in MU firing rate variability apparent in the trained limb only.

physiology↗

bioRxiv2021

Motor unit recruitment strategies of the vastus lateralis according to sex

AimDespite men exhibiting greater muscle strength and fatigibility than women, it remains unclear if there are sex-based differences in muscle recruitment strategies e.g. motor unit (MU) recruitment and modulation of firing rate (FR) at normalised forces and during progressive increases in force. MethodsTwenty-nine healthy male and thirty-one healthy female participants (18-35 years) were studied. Intramuscular electromyography was used to record individual motor unit potentials (MUPs) and near fibre MUPs from the vastus lateralis (VL) during 10% and 25% maximum isometric voluntary contractions (MVC), and spike-triggered averaging was used to obtain motor unit number estimates (MUNE) of the VL. Multilevel mixed-effects linear regression models were used to investigate the effects of sex at each contraction level. ResultsMen exhibited greater muscle strength (p<0.001) and size (p<0.001) than women, with no difference in force steadiness at 10% or 25% MVC. Women had smaller MUs and higher FR at 10% MVC (both p<0.02), similar to that at 25% MVC in MU size (p=0.062) and FR (p=0.031). However, both sexes showed similar increases in MU size and FR when moving from low-to mid-level contractions. There were no sex differences in any near fibre MUP parameters or in MUNE. ConclusionIn the vastus lateralis, women produce muscle force via different neuromuscular recruitment strategies to men which is characterised by smaller MUs discharging at higher rates. However, similar strategies are employed to increase force production from low to moderate contractions. These findings of similar proportional increases between sexes support the use of mixed sex cohorts in studies of this nature. Key pointsO_LIIncreases in muscle force production are mediated by motor unit (MU) recruitment, and MU firing rate (FR). C_LIO_LIWomen are underrepresented in studies of human neuromuscular research and markedly differ to men in a number of aspects of neuromuscular function, yet little is known of the recruitment strategies of each. C_LIO_LIHere we demonstrate men and women have similar vastus lateralis MU number estimates, yet women recruit smaller MUs with higher FR than men at normalised contraction levels. However, increases in force are achieved via similar trajectories of MU recruitment and MU FR in men and women. C_LIO_LIAlthough men and women exhibit divergent neuromuscular recruitment strategies to achieve normalised forces, increases in force are achived similarly and support the inclusion of mixed sex cohorts in studies of this nature. C_LI

physiology↗