The Effect of Breathing Patterns Common to Competitive Swimming on Gas Exchange and Muscle Deoxygenation During Heavy-Intensity Fartlek Exercise

During competitive freestyle swimming, the change of direction requires a turn followed by similar to 15 m of underwater kicking at various intensities that require a similar to 5 s breath-hold (BH). Upon surfacing, breathing must be regulated, as head rotation is necessary to facilitate the breath while completing the length of the pool (similar to 25 s). This study compared the respiratory and muscle deoxygenation responses of regulated breathing vs. free breathing, during these 25-5 s cycles. It was hypothesized that with the addition of a BH and sprint during heavy-intensity (HVY) exercise, oxygen uptake (VO2) and oxygen saturation (SatO2) would decrease, and muscle deoxygenation ([HHb]) and total hemoglobin ([Hb(tot)]) would increase. Ten healthy male participants (24 +/- 3 years) performed 4-6 min trials of HVY cycling in the following conditions: (1) continuous free breathing (CONLD); (2) continuous with 5 s BH every 25 s (CONLD-BH); (3) Fartlek (FLK), a 5 s sprint followed by 25 s of HVY; and (4) a combined Fartlek and BH (FLK-BH). Continuous collection of VO2 and SatO2, [Hb(tot)], and [HHb] via breath-by-breath gas analysis and near-infrared spectroscopy (normalized to baseline) was performed. Breathing frequency and tidal volumes were matched between CONLD and CONLD-BH and between FLK and FLK-BH. As a result, VO2 was unchanged between CONLD (2.12 +/- 0.35 L/min) and CONLD-BH (2.15 +/- 0.42 L/min; p = 0.116) and between FLK (2.24 +/- 0.40 L/min) and FLK-BH (2.20 +/- 0.45 L/min; p = 0.861). SatO2 was higher in CONLD (63 +/- 1.9%) than CONLD-BH (59 +/- 3.3%; p < 0.001), but was unchanged between FLK (61 +/- 2.2%) and FLK-BH (62 +/- 3.1%; p = 0.462). Delta[Hb(tot)] is higher in CONLD (3.3 +/- 1.6 mu M) than CONLD-BH (-2.5 +/- 1.2 mu M; Delta 177%; p < 0.001), but was unchanged between FLK (2.0 +/- 1.6 mu M) and FLK-BH (0.82 +/- 1.4 mu M; p = 0.979). Delta[HHb] was higher in CONLD (7.3 +/- 1.8 mu M) than CONLD-BH (7.0 +/- 2.0 mu M; Delta 4%; p = 0.011) and lower in FLK (6.7 +/- 1.8 mu M) compared to FLK-BH (8.7 +/- 2.4 mu M; p < 0.001). It is suggested that the unchanged VO2 between CONLD and CONLD-BH was supported by increased deoxygenation as reflected by decreased Delta[Hb(tot)] and blunted Delta[HHb], via apneic-driven redistribution of blood flow away from working muscles, which was reflected by the decreased SatO2. However, the preserved VO2 during FLK-BH vs. FLK has been underpinned by an increase in [HHb].