Hypoxic Exercise Performance with an Antihistamine: Influence of Aerobic Fitness

Abstract

At altitude, impairments in pulmonary oxygen diffusion and oxygen delivery have a detrimental effect on endurance exercise tolerance. Analogues of over-the-counter antihistamines have been shown to improve oxyhemoglobin saturation (SpO2) and oxygen delivery during heavy exercise, but hypoxic performance outcomes have not been studied. PURPOSE: To determine the effect of the antihistamine, cetirizine (Zyrtec®) on hypoxic exercise performance in recreationally active subjects. METHODS: Eight subjects [6 men, 2 women; age = 22 ± 1y; V̇O2max = 44.3 ± 8.3 ml·kg-1·min-1 (range: 32.0-55.2 ml·kg-1·min-1) ] completed constant load exercise at 45% and 65% of normoxic VO2max and an 8km time trial in conditions of normoxia (NORM), hypoxia with placebo (HYP+P), and hypoxia with cetirizine (HYP+C). Subjects inspired 15% oxygen to simulate an altitude of 2,500m for HYP+P and HYP+C and were given a 10mg fixed-dose of cetirizine one hour prior to exercise for HYP+C. Measures of SpO2 via pulse oximetry and muscle tissue oxyhemoglobin concentration ([OxyHb+Mb]) of the vastus lateralis via near infrared spectroscopy were continuously measured throughout exercise. RESULTS: There was no significant difference (P ≥ 0.232) in SpO2 between HYP+P and HYP+C during the 45% (89 ± 6% vs. 89 ± 4%) and 65% (87± 6% vs. 85 ± 5%) constant loads. The cetirizine intervention had a significant effect (P = 0.005) on Δ [OxyHb+Mb] (%) during the 65% constant load with a difference between HYP+P and HYP+C (-28 ± 45% vs. +14 ± 16%). There was no difference in 8km performance times between HYP+P and HYP+C (18.08 ± 2.87 min vs. 17.03 ± 1.92 min, P = 0.112, dz= 0.63). However, when co-varied by V̇O2max, cetirizine had a significant effect (P = 0.047) on 8km time trial performance with a difference of 1.06 min (95% CI [0.01, 2.11]) between HYP+P and HYP+C. VO2max accounted for 53% of the variance in time trial performance changes between interventions. CONCLUSION: Cetirizine improves endurance exercise performance in hypoxia with a larger effect on individuals with lower V̇O2max. The cetirizine intervention resulted in greater skeletal muscle oxygenation at 65% V̇O2max with hypoxia. These results would suggest that cetirizine does not improve SpO2, but improves hypoxic exercise performance perhaps through enhanced oxygen delivery to the skeletal muscles.