Biology subjects

Piasecki, M.

Publications and source records attributed to Piasecki, M..

5 recordsLinked to original sources

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↗