Woodrow T. Murray-Wood1, Jonathan W. Specht1, Alexia S. Thiros1, Christina A. Buchanan1. Effect of Sildenafil on VO2max in Collegiate Runners Acclimatized to Moderate Altitude1High Altitude Exercise Physiology Program, Western Colorado University, Gunnison, CO, USA.


Introduction: There are many factors that contribute to reduced performance at altitude. Some of the physiological responses to hypoxia include a decreased stroke volume, decreased blood oxygen saturation, and an increase in both systemic and pulmonary vasoconstriction. Sildenafil, a potent vasodilator, inhibits phosphodiesterase type 5 which promotes vasodilation via the augmentation of intracellular cGMP. Methods: Eight well-trained men (18.5 ± 0.53 yrs), acclimatized to 2348m, were asked to complete three graded exercise tests: A familiarization test, one after taking 50mg orally-ingested sildenafil (SIL) and one with a placebo (PLA). Subjects began the test on the treadmill at a speed of 8mph and a grade of 0%. Speed remained the same and grade was increased 1% each minute until volitional fatigue was reached. Performance was determined by measuring heart rate (HR), blood pressure (BP), time to exhaustion (TTE), blood oxygen saturation (SpO2), rating of perceived exertion (RPE), and maximal oxygen consumption (VO2max). HR and VO2max were continually monitored, while RPE was measured every minute and SpO2 data was collected every two minutes. BP was measured at rest, at maximal effort (immediately following volitional fatigue), and five minutes post completion. SPSS version 25.0 was used to run a paired-samples t-test for each independent variable and for both groups (PLA vs SIL). Results: TTE significantly increased in the SIL group compared to PLA (631.25 ± 52.07 vs. 584.63 ± 51.58, p<.001) as well as average SpO2 (87.5 ± 2.05% vs. 92.6 ± 1.53%, p<.002). VO2max decreased in the SIL group compared to PLA (62.38 ± 3.51 vs. 63.43 ± 3.52) though not significantly (p>0.05). Systolic BP at maximal effort decreased in the SIL group compared to PLA (156.88 ± 3.48 vs. 134.38 ± 11.48, p<.001). Conclusions: Athletes training or competing at altitude may see an increase in performance with sildenafil. This research is preliminary and further research should include a larger subject pool, a shorter timeframe for data collection, and additional performance measures such as a live race/competition.