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Features of gas exchange in advanced level freediver during monofin practice in pool

During a monofin freedive in pool an athlete goes into hypercapnia and hypoxia. This limits his or her performance. During breatholds the air stored in the lungs and airways is changing it’s composition. The changes are poorly studied, or not at all for advanced level freedivers. Some research was done on spearfishers, which is a poor approximation of freediving. We analyzed the end-tidal air of an advanced level freediver in pool training. Continuous freedives under 60% of personal bests, or interval series with each dive under 20-40% of personal best lead to moderate hypoxia and acute hypercapnia and are good for laying-the-bases training periods, increasing personal tolerance to CO2 (though this will not directly improve athletic performance). On the other hand, for pre-competitive training periods for experienced freedivers we recommend continuous one-time dives (with a safety buddy) at distances over 70% of personal best.