The Effects Of Ischemic Preconditioning On Endurance Running Performance In The Heat

Exercising in the heat results in decreased performance due to heightened physiological stress. Ischemic preconditioning (IPC) has been shown to be a novel strategy for improving endurance performance in a thermoneutral environment. Few studies have examined the effects of IPC on endurance exercise in the heat. PURPOSE: This study aimed to investigate the effects of IPC on endurance performance and evaluate whether IPC would attenuate heat-induced physiological stress. METHODS: Using a randomized crossover design, twelve healthy young subjects (8 men/ 4 women) performed a 6-min moderate-intensity exercise (EX1) and a time to exhaustion test at a heavy-intensity (EX2) in a hot environment (35 °C, 50 % RH), preceded by an IPC (4 × 5 min occlusion at 220 mmHg) or SHAM (4 × 5 min occlusion at 20 mmHg) procedure. For the IPC session, the cuffs were placed on the uppermost portion of the thigh and inflated in an alternating fashion for 5-min bouts. To ensure a sufficient rest interval between the treatment and exercise, a 20-min recovery period followed by treatment. During all trails, we measured stroke volume, heart rate, cardiac output, pulmonary V̇O2 kinetics, muscle oxygen saturation, skin blood flow, and core temperature. RESULTS: IPC significantly increased total running time in the heat compared with SHAM (IPC: 416.4 ± 61.9 s vs SHAM 389.3 ± 40.7 s, p = 0.027). During the EX2, IPC significantly increased stroke volume (IPC: 154.7 ± 33.8 ml vs SHAM: 127.7 ± 16.3 ml, p = 0.002), cardiac output (IPC: 27.6 ± 5.9 L/min vs SHAM: 24.2 ± 3.0 ml/min, p = 0.013), the end-exercise of V̇O2 (IPC: 3.72 ± 0.85 L/min-1 vs SHAM: 3.54 ± 0.87 L/min-1, p = 0.017) and slow phase amplitude (IPC: 0.72 ± 0.22 L/min-1 vs SHAM: 0.57 ± 0.17 L/min-1, p = 0.016) compared with SHAM. During the recovery phase, IPC significant increased skin blood flow compared to BL (VL, BL: 91.2 ± 14.4 au vs Recovery: 119.2 ± 32.4 au, p = 0.001; GA, BL: 48.4 ± 16.1 au vs Recovery: 59.4 ± 19.1 au, p = 0.025). There was less core temperature increase following IPC compared with SHAM during EX1 (IPC: 0.18 ± 0.06 °C vs SHAM: 0.22 ± 0.08 °C, p = 0.005) and EX2 (IPC: 0.87 ± 0.10 °C vs SHAM: 1.03 ± 0.10 °C, p < 0.001). CONCLUSIONS: IPC effectively mitigates the physiological stress induced by the thermal environment during exercise, then has the potential to improve endurance performance.