Swimmers can train in hypoxia at sea level through voluntary hypoventilation

• We measured blood oxygenation in swimmers thanks to a waterproofed forehead sensor.
• Voluntary hypoventilation at low lung volume induced severe hypoxemia in swimmers.
• Hypoventilation at low lung volume increased the solicitation of anaerobic glycolysis.
• Voluntary hypoventilation at high lung volume did not lead to hypoxemia in swimmers.
• Hypoventilation at high lung volume decreased the glycolytic stimulus in swimmers.

This study used an innovative technique of pulse oximetry to investigate whether swimmers can train under hypoxic conditions through voluntary hypoventilation (VH). Ten trained subjects performed a front crawl swimming series with normal breathing (NB), VH at high (VHhigh) and low pulmonary volume (VHlow). Arterial oxygen saturation was continuously measured via pulse oximetry (SpO2) with a waterproofed forehead sensor. Gas exchanges were recorded continuously and lactate concentration ([La]) was assessed at the end of each test. In VHlow, SpO2 fell down to 87% at the end of the series whereas it remained above 94% in VHhigh during most part of the series. Ventilation, oxygen uptake and end-tidal O2 pressure were lower in both VHhigh and VHlow than in NB. Compared to NB, [La] significantly increased in VHlow and decreased in VHhigh. This study demonstrated that swimmers can train under hypoxic conditions at sea level and can accentuate the glycolytic stimulus of their training if they perform VH at low but not high pulmonary volume.