Biology subjects

Maeo, S.

Publications and source records attributed to Maeo, S..

4 recordsLinked to original sources

bioRxiv2026

Muscle-specific reticulospinal contributions to limb-trunk coordination during standing arm curls in strength-trained and untrained individuals

Limb-trunk coordination plays an essential role in daily actions. The reticulospinal excitability of limb muscles has been suggested to be modulated by long-term motor experience, such as strength training. However, it remains unclear whether reticulospinal contributions in the limb and trunk muscles during limb-trunk coordinated movements are modulated by strength training. This study aimed to determine whether reticulospinal contributions to limb-trunk coordination differ between strength-trained and untrained individuals. Fifteen long-term ([≥]3 yrs) strength-trained and 15 untrained healthy men participated in this study. Participants performed a rapid bilateral arm-curl task while standing, using a load corresponding to 35% of their one-repetition maximum, in response to visual, visual-auditory (80 dB), or visual-startling (115 dB) stimuli. Electromyography (EMG) was recorded from the right biceps brachii (BB) and erector spinae (ES) muscles during the task. In the trained group, EMG onset of the ES was closer to that of the BB than in the untrained group, indicating tighter temporal coordination between the limb prime mover and trunk postural muscles in strength-trained individuals. In both groups, visual-startling stimuli shortened the EMG onset of both the BB and ES, suggesting reticulospinal contributions to both muscles. Notably, the reduction in EMG onset of the BB induced by the startling stimulus was smaller in the trained group than in the untrained group, whereas no difference between groups was observed for the ES. These findings suggest that long-term strength training may modify limb-trunk muscle coordination during standing arm curls and may be associated with muscle-specific adaptations in reticulospinal contributions.

neuroscience↗

bioRxiv2024

Motor unit discharge properties of the vastii muscles and their modulation with contraction level depend on the knee-joint angle

This study examined the effect of the knee-joint angle on motor unit (MU) discharge properties of the vastii muscles and their modulation with contraction level. Twelve young adults performed unilateral isometric knee-extension contractions during three experimental sessions at either 25, 55, and 85{degrees} of knee flexion (full extension: 0{degrees}) in a randomised order. Each session involved maximal voluntary contractions (MVCs) followed by submaximal trapezoidal and triangular contractions at different levels relative to maximal voluntary torque (MVT). High-density surface electromyograms were recorded from vastus lateralis and medialis muscles and, subsequently, decomposed to obtain discharge timings of individual MUs. MVT was the greatest, whereas MU discharge rate (DR) during MVCs and submaximal contraction levels ([≥]30% MVT) was the lowest at the intermediate joint angle (55{degrees}). The highest DR during MVCs and high-level contractions (70% MVT), however, was at the most flexed knee position (85{degrees}), which was due to a greater DR increase 50-70% MVT compared to 25{degrees} and 55{degrees}. The onset-offset DR hysteresis ({Delta}F), an estimate of persistent inward current contribution to motoneuron discharge, decreased with knee flexion and increased with contraction level, whereas the degree of motoneuron input-output nonlinearity (brace height) did not vary with joint angle but decreased with contraction level. At 85{degrees}, {Delta}F increased more and brace height decreased less with contraction level compared to 25{degrees} and 55{degrees}. These findings indicate that vastii MU DR and its modulation with contraction level vary with knee-joint angle, which could be partly explained by the modulation of motoneuron intrinsic electrical properties. NEW & NOTEWORTHYThis study explored the relationship between motoneuron output to the vastii muscles at different knee-joint angles (quadriceps lengths) and isometric contraction levels. We showed that the motor unit discharge rate was lowest at the angle of the greatest absolute torque capacity, whereas the contraction-level-induced increases in discharge rate and motoneuron excitability were the greatest in the flexed position. These findings suggest that joint-angle-dependent adjustments in sensory feedback modulate motor control of the knee-extensor muscles.

physiology↗

bioRxiv2022

Non-invasive muscle biopsy: estimation of muscle fibre size from a neuromuscular interface

Because of the biophysical relation between muscle fibre diameter and the propagation velocity of action potentials along the muscle fibres, motor unit conduction velocity (MUCV) could be a non-invasive index of muscle fibre size in humans. However, the relation between MUCV and fibre size has been only assessed indirectly in animal models and in human patients with invasive intramuscular EMG recordings, or it has been mathematically derived from computer simulations. By combining advanced non-invasive techniques to record motor unit activity in vivo, i.e., high-density surface EMG, with the gold standard technique for muscle tissue sampling, i.e., muscle biopsy, here we investigated the relation between the conduction velocity of populations of motor units identified from the biceps brachii muscle, and muscle fibre diameter. Moreover, we demonstrate the possibility to predict muscle fibre diameter (R2 = 0.66) and cross-sectional area (R2 = 0.65) from conduction velocity estimates with low systematic bias (~2% and ~4% respectively) and a relatively low margin of individual error (~8% and ~16%, respectively). The proposed neuromuscular interface opens new perspectives in the use of high-density EMG as a non-invasive tool to estimate muscle fibre size without the need of surgical biopsy sampling. The non-invasive nature of high-density surface EMG for the assessment of muscle fibre size may be useful in studies monitoring child development, aging, space and exercise physiology. SIGNIFICANCE STATEMENTOur study explored the relation between the conduction velocity of populations of motor units and muscle fibre size in healthy humans. Our results provide in vivo evidence that a high-density surface EMG-derived physiological parameter, i.e. motor unit conduction velocity, can be adopted to estimate muscle fibre size, without the need of surgical biopsy sampling. Here we propose a neuromuscular interface that opens new perspectives not only in the study of neuromuscular disorders, but also in other fields where the non-invasive and painless determination of muscle fibre and motor unit size becomes a priority, such as in aging, space and exercise physiology.

physiology↗

bioRxiv2022

Neural decoding from surface high-density EMG signals: influence of anatomy and synchronization on the number of identified motor units

ObjectiveHigh-density surface electromyography (HD-sEMG) allows the reliable identification of individual motor unit (MU) action potentials. Despite the accuracy in decomposition, there is a large variability in the number of identified MUs across individuals and exerted forces. Here we present a systematic investigation of the anatomical and neural factors that determine this variability. ApproachWe investigated factors of influence on HD-sEMG decomposition, such as synchronization of MU discharges, distribution of MU territories, muscle-electrode distance (MED - subcutaneous fat thickness), maximum anatomical cross-sectional area (ACSAmax), and fiber CSA. For this purpose, we recorded HD-sEMG signals, ultrasound, magnetic resonance imaging, and muscle biopsy of the biceps brachii muscle from two groups of participants - untrained-controls (UT=14) and strength-trained (>3 years of training, ST=16) - while they performed isometric ramp contractions with elbow flexors (at 15, 35, 50 and 70% maximum voluntary torque - MVT). We assessed the correlation between the number of accurately detected MUs by HD-sEMG decomposition and each measured parameter, for each target force level. Multiple regression analysis was then applied. Main resultsST subjects showed lower MED (UT: 4.8 {+/-} 1.4 vs. ST: 3.7 {+/-} 0.8 mm) associated to a greater number of identified motor units (UT: 21.3 {+/-} 10.2 vs. ST: 29.2 {+/-} 11.8 MUs/subject). Both groups showed a negative correlation between MED and the number of identified MUs at low forces (r= -0.6, p=0.002 at 15% MVT). Moreover, the number of identified MUs was positively correlated to the distribution of MU territories (r=0.56, p=0.01) and ACSAmax (r=0.48, p=0.03) at 15% MVT. By accounting for all anatomical parameters, we were able to partly predict the number of decomposed MUs at low but not at high forces. SignificanceOur results confirmed the influence of subcutaneous tissue on the quality of HD-sEMG signals and demonstrated that MU spatial distribution and ACSAmax are also relevant parameters of influence for current decomposition algorithms.

bioengineering↗