Neuromuscular responses to fatiguing locomotor exercise

Abstract

Over the last two decades, an abundance of research has explored the impact of fatiguing locomotor exercise on the neuromuscular system. Neurostimulation techniques have been implemented prior to and following locomotor exercise tasks of a wide variety of intensities, durations, and modes. These techniques have allowed for the assessment of alterations occurring within the central nervous system and the muscle, while techniques such as transcranial magnetic stimulation and spinal electrical stimulation have permitted further segmentalization of locomotor exercise‐induced changes along the motor pathway. To this end, the present review provides a comprehensive synopsis of the literature pertaining to neuromuscular responses to locomotor exercise. Sections of the review were divided to discuss neuromuscular responses to maximal, severe, heavy and moderate intensity, high‐intensity intermittent exercise, and differences in neuromuscular responses between exercise modalities. During maximal and severe intensity exercise, alterations in neuromuscular function reside primarily within the muscle. Although post‐exercise reductions in voluntary activation following maximal and severe intensity exercise are generally modest, several studies have observed alterations occurring at the cortical and/or spinal level. During prolonged heavy and moderate intensity exercise, impairments in contractile function are attenuated with respect to severe intensity exercise, but are still widely observed. While reductions in voluntary activation are greater during heavy and moderate intensity exercise, the specific alterations occurring within the central nervous system remain unclear. Further work utilizing stimulation techniques during exercise and integrating new and emerging techniques such as high‐density electromyography is warranted to provide further insight into neuromuscular responses to locomotor exercise.

A single bout of downhill running attenuates subsequent level running-induced fatigue

“…In accordance with the literature, the LR was performed in the heavy intensity domain (i.e., above the LT), which involves exercises with duration between ~ 40 min and 3 h 17 , 18 . The impairment of neuromuscular function at these exercise intensities can be explained by central and peripheral mechanisms such as decreased neural drive, compromised motoneuron excitability and failure in excitation–contraction coupling, among others 19 . Specific alterations occurring within the central nervous system involved in the strength loss within the heavy intensity domain have not yet been fully understood 19 .…”

“…The impairment of neuromuscular function at these exercise intensities can be explained by central and peripheral mechanisms such as decreased neural drive, compromised motoneuron excitability and failure in excitation–contraction coupling, among others 19 . Specific alterations occurring within the central nervous system involved in the strength loss within the heavy intensity domain have not yet been fully understood 19 . However, studies have shown a greater reduction in voluntary activation when compared to the severe intensity domain 20 , 21 .…”

“…Therefore, it is possible to hypothesize that the factors that determined the lower strength loss after LR can be predominantly related to peripheral factors. Peripherally, the strength loss during exercise performed within the heavy intensity domain may be related to depletion of glycogen stores, and to increased production of reactive nitrogen and oxygen species, which seem to interfere with Ca 2+ release (for details, please see Brownstein et al 19 ). Additionally, in running, which involves the stretching-shortening cycle, the myofibrillar disintegration and the disorganization of sarcomeres generated by muscle damage can also contribute to the strength loss observed in the present study, especially 48 h post-LR 26 .…”

Physical exercise—A toxin‐free complement to cancer therapy

“…Physical exercise can counteract many cancer promoting factors, such as high inflammatory levels, high levels of adipose tissue, cachexia, cardiovascular diseases 5 and a low mitochondrial capacity. Therefore, researchers are more and more eager to understand the molecular mechanisms that promote the manifold of effects that exercise can have on our physiology 6‐9 …”

Quantification of central fatigue: a central debate

“…However, the ongoing debate surrounds the quantification of central fatigue. The twitch interpolation technique offers the advantage to be easily quantified but it is mostly limited to maximal isometric contraction and the relevance of the reduction in voluntary activation to exercise performance during submaximal intensity tasks is unclear (Brownstein et al 2021). In their review, Dotan et al (2021) advance several arguments suggesting that the variables used for the calculation of voluntary activation are affected by peripheral factors or factors independent of muscle fatigue, questioning the use of the twitch interpolation technique to determine central fatigue.…”