Effects of induced local ischemia during a 4-km cycling time trial on neuromuscular fatigue development

Abstract

The present study analyzed the effects of local ischemia during endurance exercise on neuromuscular fatigue (NMF). Nine cyclists performed, in a counterbalanced order, two separate 4-km cycling time trials (TT) with (ISCH) or without (CONTR) induced local ischemia. NMF was characterized by using isometric maximal voluntary contractions (IMVC), while central [voluntary activation (VA)] and peripheral fatigue [peak torque of potentiated twitch (TwPt)] of knee extensors were evaluated using electrically-evoked contractions performed before (PRE) and 1 min after (POST) the TT. Electromyographic activity (EMG), power output (PO), oxygen uptake (V̇O2) and rating of perceived exertion (RPE) were also recorded. The decrease in IMVC (-15±9% vs -10±8 %, P=0.66), VA (-4±3% vs -3±3%, P=0.46), and TwPt (-16±7% vs -19±14%, P=0.67) were similar in ISCH and CONTR. Endurance performance was drastically reduced in ISCH condition (512±29 s) compared to CONTR (386±17 s) (P<0.001), which was accompanied by lower EMG, PO, and V̇O2 responses (all P<0.05). RPE was greater in ISCH compared to CONTR (P < 0.05), but the rate of change was similar throughout the TT (0.016±0.005 and 0.020±0.006 RPE·s-1, respectively; P>0.05). These results indicate that similar end-exercise NMF levels were accompanied by impaired endurance performance in ISCH compared to CONTR. These novel findings suggest that the local reduced oxygen availability affected the afferent feedback signals to the central nervous system, ultimately increasing perceived effort and reducing muscle activity and exercise intensity in order to avoid surpassing a sensory tolerance limit before the finish line.

Prior Involvement of Central Motor Drive Does Not Impact Performance and Neuromuscular Fatigue in a Subsequent Endurance Task

“…Rather, it is more plausible that inhibitory feedback coming from group III/IV muscle afferents played an important role in exercise termination. The observation from this and previous studies (12,44–46) that exercise cessation coincides with similar and consistent levels of decline in Q tw,pot (Fig. 3C) supports the concept of the existence of a “critical threshold of peripheral fatigue.” This idea proposes that metabolic perturbation (and therefore peripheral fatigue) is a tightly monitored and regulated variable, which, through group III/IV afferents-mediated feedback, lead the central nervous system to restrict motoneuronal output and promote central fatigue, to limit the disturbance to the muscle homeostasis.…”

“…Rather, it is more plausible that inhibitory feedback coming from group III/IV muscle afferents played an important role in exercise termination. The observation from this and previous studies (12,(44)(45)(46) that exercise cessation coincides with similar and consistent levels of decline in Q tw,pot (Fig. 3C) supports the concept of the existence of a "critical threshold of peripheral fatigue."…”

Intervention Effect of Long-Term Aerobic Training on Anxiety, Depression, and Sleep Quality of Middle School Students With Depression After COVID-19

“…However, without real-time heart rate monitoring equipment, this intensity is considerably difficult to monitor. The RPE method used in this study to monitor exercise intensity is a subjective feeling based on heart rate intensity and has a very wide range of applications in the field of competitive sports ( 25 ). The authors of the current paper attempted to introduce it into this study to provide assistance in monitoring the intensity of the subjects throughout the exercise cycle.…”