The neuromechanical delay of the vastii muscles lengthens during a voluntary isometric contraction to exhaustion
Krätschmer R, Paternoster FK, Del Vecchio A (2026)
Publication Type: Journal article
Publication year: 2026
Journal
Book Volume: 140
Pages Range: 1732-1743
Journal Issue: 6
DOI: 10.1152/japplphysiol.01134.2025
Abstract
The latency between neural drive to a muscle and the resulting force production during continuous contractions is described by the neuromechanical delay (NMD). NMD shortens with increasing contraction intensity and speed, varies between muscle groups and fascicle lengths, and lengthens under pain sensation. However, it remains unclear how NMD changes during fatigue. We investigated the NMD of the vastii muscles during a sustained sinusoidal contraction performed to exhaustion. Ten healthy adults (9 males) performed maximum voluntary contractions (pre-MVCs), the biofeedback-controlled contraction to exhaustion at a mean force of 30% MVC, and a post-MVC. High-density electromyographic signals were recorded from the vastii muscles and decomposed into motor unit discharge timings. Cross-correlation between neural drive and force was used to determine NMD as the time lag between the two signals. We did not find any differences in neural drive measures or NMD between muscles (P > 0.05). Post-MVC force was significantly reduced by 19% compared with pre-MVC (P < 0.001). NMD increased from 113 (±19) to 168 (±16) ms from the initial 10% to 100% of exhaustion time (P < 0.001). The observed NMD prolongation likely reflects slowed and diminished force transmission due to fatigue-induced accumulation of myofibrillar metabolites, which alter twitch characteristics and mechanical properties of the motor units. Prolongation of the NMD may serve as a key indicator of fatigue, as delays in action potential transmission to force production can generate inhomogeneous muscle forces, thereby potentially increasing the risk of injury. NEW & NOTEWORTHY This is the first study to demonstrate that the latency between neural drive and muscle force production lengthens with fatigue during voluntary contractions. Although prior research reported fatigue-related increases in electromechanical delay, these findings come from electrically evoked contractions or the initiation of voluntary contractions from resting muscle. Our approach enables the analysis of neural and force signals during naturally controlled muscle contractions, offering new insight into fatigue-induced changes in neuromuscular function under physiological conditions.
Authors with CRIS profile
Involved external institutions
Germany (DE)How to cite
APA:
Krätschmer, R., Paternoster, F.K., & Del Vecchio, A. (2026). The neuromechanical delay of the vastii muscles lengthens during a voluntary isometric contraction to exhaustion. Journal of Applied Physiology, 140(6), 1732-1743. https://doi.org/10.1152/japplphysiol.01134.2025
MLA:
Krätschmer, Rafael, Florian Kurt Paternoster, and Alessandro Del Vecchio. "The neuromechanical delay of the vastii muscles lengthens during a voluntary isometric contraction to exhaustion." Journal of Applied Physiology 140.6 (2026): 1732-1743.
BibTeX: Download