TY - JOUR
T1 - Neural control of matched motor units during muscle shortening and lengthening at increasing velocities
AU - Oliveira, Anderson Souza
AU - Negro, Francesco
PY - 2021
Y1 - 2021
N2 - Modulation of movement velocity is necessary during daily life tasks, work, and sports activities. However, assessing motor unit behavior during muscle shortening and lengthening at different velocities is challenging. High-density surface electromyography (HD-sEMG) is an established method to identify and track motor unit behavior in isometric contractions. Therefore, we used this methodology to unravel the behavior of the same motor units in dynamic contractions at low contraction velocities. Velocity-related changes in tibialis anterior motor unit behavior during concentric and eccentric contractions at 10 and 25% maximum voluntary isometric contraction were assessed by decomposing HD-sEMG signals recorded from the tibialis anterior muscle of eleven healthy participants at 5°/s, 10°/s, and 20°/s. Motor units extracted from the dynamic contractions were tracked across different velocities at the same load levels. On average, 14 motor units/participant were matched across different velocities, showing specific changes in discharge rate modulation. Specifically, increased velocity led to an increased rate of change in discharge rate (e.g., discharge rate slope, p=0.025), recruitment and derecruitment discharge rates (p=0.003 and p=0.001), and decreased recruitment angles (p=0.0001). Surprisingly, the application of the motor unit extraction filters calculated from 20°/s onto the recordings at 5°/s and 10°/s revealed that >92% of motor units recruited at the highest velocity were active on both lower velocities, indicating no additional recruitment of motor units. Our results suggest that motor unit rate coding rather than recruitment is responsible for controlling muscle shortening and lengthening contractions at increasing velocities against a constant load.
AB - Modulation of movement velocity is necessary during daily life tasks, work, and sports activities. However, assessing motor unit behavior during muscle shortening and lengthening at different velocities is challenging. High-density surface electromyography (HD-sEMG) is an established method to identify and track motor unit behavior in isometric contractions. Therefore, we used this methodology to unravel the behavior of the same motor units in dynamic contractions at low contraction velocities. Velocity-related changes in tibialis anterior motor unit behavior during concentric and eccentric contractions at 10 and 25% maximum voluntary isometric contraction were assessed by decomposing HD-sEMG signals recorded from the tibialis anterior muscle of eleven healthy participants at 5°/s, 10°/s, and 20°/s. Motor units extracted from the dynamic contractions were tracked across different velocities at the same load levels. On average, 14 motor units/participant were matched across different velocities, showing specific changes in discharge rate modulation. Specifically, increased velocity led to an increased rate of change in discharge rate (e.g., discharge rate slope, p=0.025), recruitment and derecruitment discharge rates (p=0.003 and p=0.001), and decreased recruitment angles (p=0.0001). Surprisingly, the application of the motor unit extraction filters calculated from 20°/s onto the recordings at 5°/s and 10°/s revealed that >92% of motor units recruited at the highest velocity were active on both lower velocities, indicating no additional recruitment of motor units. Our results suggest that motor unit rate coding rather than recruitment is responsible for controlling muscle shortening and lengthening contractions at increasing velocities against a constant load.
KW - Dynamic
KW - Eccentric
KW - Motor unit
KW - Neural drive
KW - Shortening
UR - http://www.scopus.com/inward/record.url?scp=85108303439&partnerID=8YFLogxK
U2 - 10.1152/japplphysiol.00043.2021
DO - 10.1152/japplphysiol.00043.2021
M3 - Journal article
C2 - 33955258
SN - 8750-7587
VL - 130
SP - 1798
EP - 1813
JO - Journal of Applied Physiology
JF - Journal of Applied Physiology
IS - 6
ER -