Physiologists thought the human body’s limit for diving was 30 meters until Jacques Mayol dove to 70.4 meters in 1968, shattering this belief. Herbert Nitsch set a world record at 214 meters in 2007, challenging physiologists even further. Free diving involves descending and returning with one breath, facing extreme pressures and no access to oxygen. Critical physiological responses, such as the mammalian diving reflex and the frog breathing technique, enable divers to reach such depths. Mental adaptation is crucial, as divers must go against the urge to breathe. Safety divers are present to prevent shallow water blackout and drowning. The maximum diving depth is still being investigated, with advanced techniques suggesting a potential limit of 320 meters.
https://www.mcgill.ca/oss/article/student-contributors-did-you-know/how-deep-can-humans-really-go