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Thesis Format

Integrated Article


Master of Science




Belfry, Glen R.


The purpose of this study was to compare the respiratory and muscle deoxygenation (HHb) responses of regulated breathing versus free-breathing, during continuous exercise (CONLD) and intermittent 5s breath holds (BH) (CONLD-BH), intermittent 5s sprint (FLK) and combined 5s BH and sprint (FLK-BH) followed by 25s of free-breathing. Oxygen uptake(V̇O2)was unchanged between CONLD (2.12±0.35L/min) and CONLD-BH (2.15±0.42L/min; p=0.116), and FLK (2.24±0.40L/min) and FLK-BH (2.20±0.45L/min; p=0.861). Δ[Hbtot]: CONLD (3.3±1.6µM) > CONLD-BH (-2.5±1.2µM; ∆177%; p<0.001), but unchanged between FLK (2.0±1.6µM) and FLK-BH (0.82±1.4µM; p=0.979). Δ[HHb]: CONLD (7.3±1.8µM) > CONLD-BH (7.0±2.0µM; ∆4%; p=0.011), and FLK (6.7±1.8µM) < FLK-BH (8.7±2.4µM; p<0.001). It is suggested that the unchanged V̇O2 between CONLD and CONLD-BH was supported by increased deoxygenation, reflected by decreased ∆[Hbtot] and blunted ∆[HHb], via apneic-driven redistribution of blood flow away from working muscles, which is reflected by the decreased SatO2. However, the preserved V̇O2 during FLK-BH versus FLK has been underpinned by the increase [HHb].

Summary for Lay Audience

Breath holds (BH) during exercise restrict oxygen transport to tissues, which hinders the working muscles’ ability to maintain the required energy demand. This is because oxygen is required for one of the major energy regeneration processes, aerobic metabolism. In aquatic sports such as swimming, irregular breathing and BH patterns limit gas exchange at the lungs, including oxygen uptake and carbon dioxide (CO2) removal. Since the rate of oxygen consumption (V̇O2) ultimately reflects the rate of aerobic metabolism, it was expected that V̇O2 would be lower compared to similar exercises on land.

Near infrared spectroscopy (NIRS) can be used to measure regional oxyhemoglobin concentrations non-invasively. Deoxyhemoglobin (HHb) represents successful offloading of oxygen from hemoglobin (Hb) and myoglobin (Mb). Total hemoglobin (Hbtot) reflects the number of Hb under the NIRS probe.

In the present study, we were interested in the effects of a free-breathing protocol constant load (CONLD) compared to a regulated breathing strategy common to front crawl swimming. To mimic swimming 50 m laps, repeated cycles of 5 s BHs performed every 30 s were employed. During the 25 s, breathing frequency was matched to the same period of the free-breathing protocol (CONLD-BH). In two other conditions, a periodic sprint was performed every 30 s under normal (FLK) and BH conditions (FLK-BH) during the 5 s intervals. Breathing was also regulated between FLK and FLK-BH during the non-apneic 25 s intervals. Mean V̇O2 was unchanged between CONLD and CONLD-BH. However, [Hbtot] was lower in CONLD-BH, perhaps reflecting reduced regional blood flow to the muscle. [HHb] was also lower in CONLD-BH, however, [Hbtot] was minimally affected. This suggests that the muscle under investigation (quadriceps) was relying on increased deoxygenation. The observed redistribution of blood flow away from working muscles allows deep diving athletes to reach further depths. Elite deep divers can maintain the V̇O2 required by their exhaustive efforts while simultaneously rerouting drastic volumes of blood to central organs.

V̇O2 was also unchanged between FLK and FLK-BH. This BH resolution was expressed by an increase in [HHb] reflecting greater muscle oxygenation from Hb. Therefore, both protocols resolved unchanged V̇O2 through increased oxygen offloading from Hb.