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.