Biology subjects

Pourreza, E.

Publications and source records attributed to Pourreza, E..

4 recordsLinked to original sources

bioRxiv2026

Neural and mechanical properties of vastus lateralis and vastus medialis at different rectus femoris muscle lengths

This study investigated how altering the length of one muscle influences motor unit discharge behavior of its synergists. Eighteen participants performed isometric knee extensions at 10% and 30% of maximal voluntary contraction (MVC) with the hip joint at 90{degrees} (shortened rectus femoris, RF) and 180{degrees} (lengthened RF). High-density surface electromyograms were recorded from vastus medialis, RF and vastus lateralis, and decomposed into motor unit spike trains. Mean discharge rate and coefficient of variation of interspike interval were analyzed for tracked units in the vasti and non-tracked in the RF. While no changes were observed in RF motor units, lengthening the RF led to increased discharge rates of vasti motor units at 10% MVC, but not 30% MVC. To further explore these force-dependent changes, two further experiments were conducted. The first showed that the discharge rate at recruitment during ramp-up contractions increased with RF lengthening, but only for low-threshold vasti units. In the second, electrically evoked twitch contractions in the vasti revealed significantly reduced twitches at 180{degrees} during low-frequency, but not high-frequency stimulation. These findings collectively suggest that the force-dependent changes in the vasti motor unit discharge rates are likely driven by RF-length dependent changes in the vasti muscles contractile properties.

physiology↗

bioRxiv2025

Motor unit rate coding in intrinsic hand muscles during isolated finger contractions and pinch task

PurposeMuscle force output is modulated via motor unit recruitment and rate coding, yet how rate coding in intrinsic hand muscles differs between isolated and synergistic hand tasks remains unclear. This study examined motor unit discharge behaviour in the first dorsal interosseous (FDI) and thenar during isolated index finger flexion, isolated thumb flexion, and a tip pinch task. MethodsSeventeen participants performed each task at 10%, 20%, and 30% of their maximal voluntary contraction (MVC) while high-density surface electromyograms (HDsEMG) were recorded from both muscles. Motor unit spike trains were completely decomposed from the HDsEMG recordings, tracked across force levels, and their mean discharge rates and recruitment thresholds were calculated. ResultsFor both FDI and thenar muscles, the mean discharge rate increased with force, but the FDI exhibited steeper slopes than the thenar and at 10-20% MVC than 20%-30% MVC. In addition, lower recruitment thresholds and higher mean discharge rates were observed in the FDI compared to the thenar. Task-dependent differences were also observed in the FDI, with the pinch task yielding higher discharge rates than isolated contractions. In the thenar, differences between tasks were limited to higher forces. ConclusionThese findings demonstrate muscle- and task-specific motor unit modulation across forces in the intrinsic hand muscles, where the FDI relies more on rate coding, while the thenar likely prioritizes recruitment to cope with increased force demands.

physiology↗

bioRxiv2025

Differential changes in the effective neural drive following new motor skill acquisition between vastus lateralis and medialis

PurposeTo investigate whether short-term learning of a new motor task is mediated by changes in common synaptic inputs to motor neurons within and between synergistic muscles. MethodsSeventeen healthy individuals performed 15 repetitions of a complex force-matching task at 10% of a maximal voluntary contraction. Two trials were selected for analysis, the one with the highest force-target error (pre-learning) and the one with the lowest (post-learning). High-density surface electromyograms recorded from vastus medialis (VM) and vastus lateralis (VL) were decomposed into their constituent motor unit spike trains, with individual motor units being tracked between trials. Motor unit discharge behavior and common synaptic oscillations across the delta, alpha, and beta bands were calculated and compared between pre- and post-learning. ResultsForce-target matching improved across trials, accompanied by a significant decrease in the coefficient of variation of the inter-spike interval (p < 0.01), while the mean discharge rate remained similar (p > 0.85). The area under the curve within delta (p < 0.003) and alpha (p < 0.004) bands decreased between trials, with no significant changes in the beta band (p > 0.05). Notably, reductions in the alpha band correlated significantly with performance improvements in VL (R = 0.81) but not in VM (R = 0.12). ConclusionThe acquisition of a new motor task is mediated by modulations in common synaptic inputs to motor units, leading to improved force control. Our findings further suggest that these changes in common synaptic inputs, particularly in the alpha band, differ between VM and VL.

neuroscience↗

bioRxiv2025

A single low-dimensional neural component of motor unit activity explains force generation across repetitive isometric tasks

Previous studies suggest that low-dimensional control underlies motor unit activity, with low-frequency oscillations in common synaptic inputs serving as the primary determinant of muscle force production. In this study, we used principal component analysis (PCA) and factor analysis (FA) to investigate the relationship between low-dimensional motor unit components and force oscillations during repetitive isometric tasks with similar force profiles. We assessed the consistency of these components across trials in both individual (tibialis anterior; first dorsal interosseous) and synergistic muscles (vastus medialis, VM; vastus lateralis, VL). Participants performed 15 trials of a force-matching learning task. Three post-skill acquisition trials were selected for analysis to ensure high similarity in force profiles. Motor units were decomposed from high-density surface electromyograms, tracked across trials, and their smoothed discharge rates were decomposed into low-dimensional components using PCA and FA. Parallel analysis indicated that a single component could explain the smoothed discharge rates for the individual muscles and two components for VM-VL. Importantly, the first component explained most of the variance ([~]70%) in smoothed discharge rates across all muscles. The first motor unit component also showed significantly higher correlations with force oscillations than the second component and remained highly consistent across trials. These findings were further supported by a non-linear framework combining network- and information-theoretic tools, which revealed high motor unit network density in the first component of all muscles. Collectively, these results suggest that, during isometric contractions, motor unit activity is primarily controlled by a single dominant shared synaptic input that closely mirrors force oscillations.

neuroscience↗