Understanding the effects of training on brain and muscle hemodynamics during exercise-induced muscle fatigue

BACKGROUND: While the muscle fatigue during weightlifting exercise is well-documented, the relationship of brain/muscle activity are less known. PURPOSE: to investigate the changes in oxygenation levels in the brain and muscles during resistance training, comparing these effects between athletes (ATH) and sedentary (SED) individuals. METHODS: 24 participants (14 SED, 10 ATH) were recruited. The bench press protocol included four sets of twelve repetitions at a weight corresponding to a Rate of Perceived Exertion (RPE) of 6. Oxygenation levels in prefrontal cortex and the right triceps muscle were continuously monitored using near-infrared spectroscopy (NIRS) (Oxymon Mk III). NIRS data was normalized relative to baseline rest values. Brain and muscle oxyhemoglobin (CerHbO, MuHbO), deoxyhemoglobin (CerHHb, MuHHb), and total hemoglobin (CertHb, MutHb) were measured. RESULTS: During the bench press exercise, MuHbO decreased in exercise set 1, 2, 3 (8.19 vs. -1.57 vs. -6.73) respectively (P < 0.05), MuHHb increased in set 1-2, and 3-4 (-6.53 vs. 9.06; 1.06 vs. 21.09) respectively (P < 0.05), and MutHb slightly decreased in set 2-3 (8.97 vs. 1.06) respectively (P < 0.05) in SED group. In ATH group, MuHbO slightly decrease in set 1-2 (7.24 vs. 5.01) respectively (P < 0.05) and slight decrease in MutHb in set 1-2 (24.62 vs. 22.40) respectively (P < 0.05). CerHbO and CertHb increased in set 3-4 (6.15 vs. 10.23; 5.39 vs. 9.97) respectively in SED (P < 0.05). CerHbO and CertHb significantly increased in set 3-4 (19.53 vs. 51.19; 28.29 vs. 64.51) respectively (P < 0.01) in ATH group. There was no statistical differences comparing muscle and brain oxygenation between SED and ATH. CONCLUSION: ATH displayed greater brain oxygenation during fatigue compared to SED, but there was little to no difference in muscle oxygenation. It may be possible ATH use different muscles to compensate for exercise-induced muscle fatigue