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

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), whereas 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 ((V)over dot(2)), 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) was similar in ISCH and CONTR. Endurance performance was drastically reduced in ISCH condition (512 +/- 29 s) compared with CONTR (386 +/- 17 s) (P < 0.001), which was accompanied by lower EMG, PO, and (V)over dot(2) responses (all P < 0.05). RPE was greater in ISCH compared with CONTR (P 0.05), but the rate of change was similar throughout the TT (8.19 +/- 2.59 vs. 7.81 +/- 2.01 RPE.% of total time -1, P> 0.05). These results indicate that similar end-exercise NMF levels were accompanied by impaired endurance performance in ISCH compared with 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 to avoid surpassing a sensory tolerance limit before the finish line.