Abstract
Ischemic preconditioning (IPC) is a strategy that may enhances endurance performance in thermoneutral environments. Exercising in the heat increases thermoregulatory and cardiovascular strain, decreasing endurance performance. The current study aimed to determine whether IPC administration improves endurance performance in the heat. In a randomized crossover design, 12 healthy subjects (V̇O(2max): 54.4 ± 8.1 mL·kg(-1)·min(-1)) underwent either IPC administration (220 mmHg) or a sham treatment (20 mmHg), then completed a moderate-intensity 6-min running (EX1) and a high-intensity time-to-exhaustion running test (EX2) in a hot environment (35 °C, 50 % RH). Cardiac function, oxygen consumption (V̇O(2)), and core body temperature (T(CORE)) were measured. During EX2, IPC administration increased the total running time in the heat compared to the sham treatment (IPC: 416.4 ± 61.9 vs. sham 389.3 ± 40.7 s, P = 0.027). IPC administration also increased stroke volume (IPC: 150.4 ± 17.5 vs. sham: 128.2 ± 11.6 ml, P = 0.008) and cardiac output (IPC: 27.4 ± 1.7 vs. sham: 25.1 ± 2.2 ml min(-1), P = 0.007) during 100% isotime of EX2. End-exercise V̇O(2) (IPC: 3.72 ± 0.85 vs. sham: 3.54 ± 0.87 L·min(-1), P = 0.017) and slow phase amplitude (IPC: 0.57 ± 0.17 vs. sham: 0.72 ± 0.22 L·min(-1), P = 0.016) were improved. When compared with the baseline period, an increase in T(CORE) was less in the IPC condition during EX1 (IPC: 0.18 ± 0.06 vs. sham: 0.22 ± 0.08 °C, P = 0.005) and EX2 (IPC: 0.87 ± 0.10 vs. sham: 1.03 ± 0.10 °C, P < 0.001). IPC improves high-intensity endurance performance in the heat by 6.9 %. This performance benefit could be associated with improved cardiac and thermoregulatory function engendered by IPC administration.