Histamine-receptor blockade does not influence the heavy-severe domain boundary and time to task failure in the severe domain during cycling exercise in adults.

The influence of histamine in skeletal muscle during exercise is poorly characterized. This investigation tested the hypothesis that histamine-receptor blockade lowers the power associated with the heavy-severe domain boundary and reduces time to task failure in the severe domain. Following a graded exercise test and a familiarization trial, 17 participants (8 M/9 F, 29 ± 8 years, VO_2peak 60.0 ± 7.5 mL/kg/min, mean ± SD) completed cycle ergometer exercise on two separate occasions, after either histamine-receptor blockade or placebo, in a double-blind randomized crossover protocol. Exercise intensities were designed to span the moderate, heavy, and severe domains. Skeletal muscle tissue oxygen saturation (%SmO₂, via near-infrared spectroscopy) and expired gases were measured continuously throughout exercise. There were no differences between blockade and placebo in power associated with the heavy-severe domain boundary (216 [195, 236] vs. 213 [191, 234] W, mean [95% CI]; p = 0.41) or time to task failure (474 [377, 572] vs. 473 [380, 566] s; p = 0.95). %SmO₂ slope decreased, and oxygen uptake increased with intensity (p < 0.01), but were not affected by blockade (all p > 0.05). These findings suggest that histamine is not crucial to supporting power at the heavy-severe domain boundary or short-duration exercise in the severe domain.