The role of the nervous system in neuromuscular fatigue induced by ultra-endurance exercise

Abstract

Ultra-endurance events are not a recent development but they have only become very popular in the last 2 decades, particularly ultramarathons run on trails. The present paper reviews the role of the central nervous system in neuromuscular fatigue induced by ultra-endurance exercise. Large decreases in voluntary activation are systematically found in ultra-endurance running but are attenuated in ultra-endurance cycling for comparable intensity and duration. This indirectly suggests that afferent feedback, rather than neurobiological changes within the central nervous system, is determinant in the amount of central fatigue produced. Whether this is due to inhibition from type III and IV afferent fibres induced by inflammation, disfacilitation of Ia afferent fibers owing to repeated muscle stretching or other mechanisms still needs to be determined. Sleep deprivation per se does not seem to play a significant role in central fatigue although it still affects performance by elevating ratings of perceived exertion. The kinetics of central fatigue and recovery, the influence of muscle group (knee extensors vs plantar flexors) on central deficit as well as the limitations related to studies on central fatigue in ultra-endurance exercise are also discussed in the present article. To date, no study has quantified the contribution of spinal modulations to central fatigue in ultra-endurance events. Future investigations utilizing spinal stimulation (i.e., thoracic stimulation) must be conducted to assess the role of changes in motoneuronal excitability on the observed central fatigue. Recovery after ultra-endurance events and the effect of sex on neuromuscular fatigue must also be studied further.

Effects of 120 vs. 60 and 90 g/h Carbohydrate Intake during a Trail Marathon on Neuromuscular Function and High Intensity Run Capacity Recovery

“…Moreover, it has been shown that mountain running endurance events have a high impact on peripheral fatigue, reducing muscle function and performance [ 3 , 20 , 58 ]. Specifically, changes in excitation–contraction (E-C) coupling failure and neuromuscular propagation reduction may contribute to a decrease in maximal force production [ 58 ].…”

“…Moreover, it has been shown that mountain running endurance events have a high impact on peripheral fatigue, reducing muscle function and performance [ 3 , 20 , 58 ]. Specifically, changes in excitation–contraction (E-C) coupling failure and neuromuscular propagation reduction may contribute to a decrease in maximal force production [ 58 ]. In the same line, downhill running induced eccentric contractions and EIMD are related to so-called low-frequency fatigue (LFF), which has been closely associated with E-C coupling failure and, as explained, with muscle force reduction [ 20 , 59 , 60 , 61 ].…”

“…Moreover, the absence of glycogen measurements might represent a major limitation that could have enabled us to understand the mechanisms of and reasons for the findings [ 72 ]. A direct assessment of both central and peripheral neuromuscular function, was not carried out using specific tools such as electrical stimulation and electromyographic recordings, as done previously in this sports discipline [ 3 , 18 , 58 ]. On the other hand, using the same speed for all participants during the high intensity run capacity (20 km/h) could be a limitation.…”

Ultra-Endurance Associated With Moderate Exercise in Rats Induces Cerebellar Oxidative Stress and Impairs Reactive GFAP Isoform Profile

“…Brain glycogen is chiefly located in these glial cells and it decreases with extensive and prolonged exercise ( Matsui et al, 2012 , 2017 ). However, it is still unknown whether UE running induces altered glial activity as well as modifies antioxidant defense mechanisms when associated with high-volume running training ( Jastrzȩbski et al, 2015 ; Rama et al, 2015 ; Knechtle and Nikolaidis, 2018 ; Millet et al, 2018 ).…”

“…The current discussion on the negative effects of high-volume and UE on runner health ( Knechtle and Nikolaidis, 2018 ; Millet et al, 2018 ), and the scarcity of knowledge about these effects in locomotion-related brain regions has motivated the present study. We hypothesized that rodent cerebellar resilience to oxidative injuries may be reduced after high-volume training, regardless of the exhaustion test simulating UE running.…”