Histamine-Receptor Antagonists Slow 10-km Cycling Performance in Competitive Cyclists

Histamine is released within skeletal muscle during exercise. In humans, antihistamines have no effect on speed, power output, or time-to-completion of short-duration high-intensity exercise. In mice, blocking histamine's actions decreases speed and duration of endurance tasks. It is unknown if these opposing outcomes are the result of differences in histamine's actions between species or are related to duration and/or intensity of exercise, as blocking histamine during endurance exercise has not been examined in humans. Purpose Determine the effects of histamine-receptor antagonism on cycling time trial performance in humans, with and without a preceding bout of sustained steady-state exercise. Methods Eleven (3F) competitive cyclists performed six 10-km time trials on separate days. The first two time trials served as familiarization. The next four time trials were performed in randomized-block order, where two were preceded by 120 min of seated rest (rest) and two by 120 min of cycling exercise (Exercise) at 50% VO2peak. Within each block, subjects consumed either combined histamine H-1 and H-2 receptor antagonists (Blockade) or Placebo, before the start of the 120-min Rest/Exercise. Results Blockade had no discernible effects on hemodynamic or metabolic variables during Rest or Exercise. However, Blockade increased time-to-completion of the 10-km time trial compared with Placebo (+10.5 +/- 3.7 s, P < 0.05). Slowing from placebo to blockade was not different between rest (+8.7 +/- 5.2 s) and Exercise (+12.3 +/- 5.8 s, P = 0.716). Conclusions Exercise-related histaminergic signaling appears inherent to endurance exercise and may play a role in facilitating optimal function during high-intensity endurance exercise.