Ischemic Preconditioning and Cycling Time Trial Performance in Hypoxia

Abstract

Ischemic preconditioning (IPC) of the legs prior to exercise has been shown as a novel approach to improve performance in a number of different exercise modes in normoxia. Very little has been done potential mechanisms behind the performance improvements in well-trained subjects, and less has been done examining the influence of these mechanisms during exercise in hypoxia. PURPOSE: To determine if IPC is an effective intervention for improving 5km cycle time trial (TT) performance in both normoxia and hypoxia. METHODS: Thirteen men (age= 24 ± 4 years, V[Combining Dot Above]2Omax= 63.1 ± 5.1 ml·kg-1·min-1) completed four randomized trials of each combination of hypoxia (F I 2O = 2 0.16) or normoxia with a resting pre-exercise IPC protocol (4 x 5min at 220mmHg) or SHAM (4 x 5min at 20mmHg) procedure. Following the IPC/SHAM protocol subjects completed two constant load bouts and a 5km time trial on a cycling ergometer. Breath-by-breath V[Combining Dot Above] O , oxyhemoglonin saturation, and skeletal muscle oxygenation/extraction (measured via near-infrared spectroscopy) were continuously monitored throughout the trials. RESULTS: IPC significantly improved 5km TT time in normoxia by 0.9 ± 1.7% compared to SHAM (IPC: 491.2 ± 33.7s vs. SHAM: 495.9 ± 34.5s, P < 0.05). IPC did not alter 5km TT performance times in hypoxia. Muscle oxygenation, extraction, and tissue saturation did not differ between treatments or inspirates (P > 0.05). CONCLUSION: IPC improves 5km cycling TT performance in normoxia only. Muscle oxygenation was unchanged suggesting that highly trained subjects choose power output based on a set level of muscular oxygenation regardless of the fraction of inspired oxygen or treatment with IPC.