FREEDIVING

Physiology This section needs expansion. You can help by adding to it. (July 2017) The human body has several oxygen-conserving adaptations that manifest under diving conditions as part of the mammalian diving reflex. The adaptations include:

Reflex bradycardia: Significant drop in heart rate. Blood-shift: Blood flow and volume is redistributed towards vital organs by means of a reflex vasoconstriction. Blood vessels distend and become engorged, which in the case of the pulmonary capillaries assists with pressure compensation that comes with increasing diving depth, and without which a largely air-filled chest cavity would simply collapse for lack of compliance. Body-cooling: peripheral vasoconstriction results in cooling of peripheral tissue beds, which lower their oxygen demand in a thermodynamic manner. In addition, Murat et al. (2013) recently discovered that breath-holding results in prompt and substantial brain cooling, just like in diving birds and seals. (Dry) breath-holds result in cooling on the order of about 1 °C/minute, but this is likely to be greater with cold water submersion, in proportion to the magnitude and promptness of the dive response. Splenic contraction: Releasing red blood cells carrying oxygen.

Techniques Breath-holding ability and, hence dive performance, is a function of on-board oxygen stores, scope for metabolic rate reduction, efficient oxygen utilization, and hypoxia tolerance. Various athletes attempt to accomplish this in various ways. Most divers rely on increasing fitness by increasing lung capacity. Some use `packing´ which increases lung volume beyond normal total lung capacity. Simple breath-holding practice is highly effective for increasing lung capacity. In addition, training is allocated to enhance blood and muscle oxygen stores, to a limited extent. A substantial proportion of performance is the result of metabolic suppression and redistribution of blood oxygen stores, the so-called dive response.

Training Training for freediving can take many forms, some of which can be performed on land.

One example is the apnea walk. This consists of a preparation "breathe-up", followed by a short (typically 1 minute) breath hold taken at rest. Without breaking the hold, the participant then initiates a walk for as far as they can, until it becomes necessary to breathe again. Athletes can do close to 400 meters in training this way.

This form of training is good for accustoming muscles to work under anaerobic conditions, and for tolerance to CO2 build-up in the circulation. It is also easy to gauge progress, as increasing distance can be measured.

Before competition attempts, freedivers perform a preparation sequence, which usually consists of physical stretching, mental exercise and breath exercise. It may include sequention of variable length static apnea and special purging deep breaths. Results of the preparation sequence are slower metabolism, lower heart rate and breath rate, lower level of CO2 in bloodstream and overall mental equilibrium.

WIKI FREEDIVING