Near Infrared Spectroscopy (NIRS) Observation of Vastus Lateralis (Muscle) and Prefrontal Cortex (Brain) Tissue...

The development of underwater Near-Infrared Spectroscopy (uNIRS) has enabled the measurement of tissue oxygenation within the swim environment. Unique physiological responses, such as the diving reflex, have been shown to occur during synchronized swimming and demonstrate an innate oxygen-conserving reflex. However, the prevalence of a sudden loss of consciousness ('hypoxic blackout') is an ongoing concern in this swim population. The purpose of this study was to investigate the reported low tissue oxygen conditions experienced in elite level synchronized swimmers (SyncS) during swim routines. Changes in peripheral muscle and brain oxygenation (Tissue Saturation Index (TSI %)) were continuously recorded during simulated synchronized swim routines. Six elite female synchronized swimmers were assessed; age 29.0 ± 4.4 years; height 168.4 ± 7.1 cm; weight 53.2 ± 3.2 kg; quadriceps skin fold; 10.2 ± 0.8 mm; ΔTSI (%) between the vastus lateralis (VL) and prefrontal cortex (PFC) were analyzed using paired (two-tailed) t-tests. The level of significance for analysis was set at p < 0.05. Significant difference (p = 0.001) was found in ΔTSI (%) between the VL and PFC. During dynamic leg kicking exercise, the initial effect of each leg kicking sequence is a rapid drop in TSI (%). This is consistent with an initial constriction (drop in blood flow in the muscle) accompanied by an increase in oxygen consumption. Cerebral oxygenation (PFC) remained largely unchanged during both maximal breath-hold and during vigorous exercise, presumably due to protective mechanisms in the brain in this population. We conclude that uNIRS is able to provide novel insights into SyncS hemodynamic responses and could be used to inform on the safety of new routines.