The effect of ischemic preconditioning and changing inspired O2 fractions on neuromuscular function during intense exercise

The aim of the present study was to determine whether ischemic preconditioning (IPC) mediated effects on neuromuscular function are dependent on tissue oxygenation. Eleven resistance-trained males completed four exercise trials (6 sets of 11 repetitions of maximal effort dynamic single-leg extensions) in either normoxic (fraction of inspired oxygen (FiO2): 21%) or hypoxic (FiO2: 14%) conditions, preceded by treatments of either IPC (3 x 5 min bilateral leg occlusions at 220 mmHg) or sham (3 x 5 min at 20 mmHg). Femoral nerve stimulation was utilized to assess voluntary activation and potentiated twitch characteristics during maximal voluntary contractions (MVCs). Tissue oxygenation (via near-infrared spectroscopy) and surface electromyography activity was measured throughout the exercise task. MVC and twitch torque declined 62% and 54%, respectively (MVC: 96 ± 24 Nm, Cohen's d= 2.9, p < 0.001; twitch torque: 37 ± 11 Nm, d= 1.6, p < 0.001), between pre-trial measurements and the sixth set without reductions in voluntary activation (p > 0.21); there were no differences between conditions. Tissue oxygenation was reduced in both hypoxic conditions compared to normoxic (p < 0.001), with an even further reduction of 3% evident in the hypoxic IPC compared to hypoxic sham trial (mean decrease 1.8 ± 0.7%, d= 1.0, p < 0.05). IPC did not affect any measure of neuromuscular function regardless of tissue oxygenation. A reduction in FiO2did invoke a humoral response and improved muscle O2extraction during exercise, however it did not manifest into any performance benefit.