The influence of cyclists` performance levels on caffeine-induced increases in neuromuscular fatigue after a 4-km cycling time trial (TT) was investigated. Nineteen cyclists performed a 4-km cycling TT 1 h after ingesting caffeine (5 mg·kg-1) or placebo (cellulose). Changes from baseline to after exercise in voluntary activation (VA) and potentiated 1 Hz force twitch (Qtw,pot) were used as markers of central and peripheral fatigue, respectively. Participants were classified as "high performing" (HP, n = 8) or "low performing" (LP, n = 8) in accordance with their performance in a placebo trial. Compared with placebo, caffeine increased the power, anaerobic mechanical power, and anaerobic work, reducing the time to complete the trial in both groups (p < 0.05). There was a group versus supplement and a group versus supplement versus trial interaction for Qtw,pot, in which the postexercise reduction was greater after caffeine compared with placebo in the LP group (Qtw,pot = -34% ± 17% vs. -21% ± 11%, p = 0.02) but not in the HP group (Qtw,pot = -22% ± 8% vs. -23% ± 10%, p = 0.64). There was no effect of caffeine on VA, but there was a group versus trial interaction with lower postexercise values in the LP group than in the HP group (p = 0.03). Caffeine-induced improvement in 4-km cycling TT performance seems to come at the expense of greater locomotor muscle fatigue in LP but not in HP cyclists.
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