How Does It Work?

Despite there being an abundance of research on CWI, the primary mechanisms for its ability to improve recovery are still not fully understood, although the following theories have been suggested:

Vasoconstriction
The theory suggests that immersion into cold water causes vasoconstriction (constriction of th blood vessels), leading to less localised blood flow. It is thought that the cold temperature activates the thermal nerve cells (nociceptors), leading to a change in sympathetic nerve activity and is therefore responsible for this reduced blood flow. This temperature-induced reduction in blood flow around the damaged tissues that is caused by strenuous exercise is thought to reduce oedemas and inflammatory activity.

Analgesic effects of the cold water
The theory postulates that the reduced perception of pain is due to the analgesic effect of the cold water. Whereby immersion into cold water leads to decreased nerve conduction speeds and excitability, thus reducing nociceptor communication with the sympathetic nervous system. Ultimately, this would lead to a reduction in the perception of pain.

Reducing inflammatory pathways
The Theory suggests that the decrease in the perception of pain is related to reduced inflammatory pathways – namely: reduced nociceptor sensitisation, reduced exercise-induced oedema (swelling), and reduced white blood cell access. This theory is a combination of effects, and is often referred to in the research as the primary physiological reason for improved recovery.

Placebo effect
The theory suggests that the effectiveness of CWI on the reduction of post-exercise pain and fatigue is primarily down to psychological perception (i.e. a placebo effect). This suggests that individual simply feels more ‘awake’ during and/or after the immersion into the cold water, causing a decrease in their sensitivity to pain. This theory is supported by a recent and extensive review which reported that CWI reduces the athlete’s perception of DOMS and RPE.

Hydrostatic Pressure

When an individual is immersed in water they are subject to the effects of hydrostatic pressure.  This hydrostatic pressure causes an inward and upward squeezing action on the body. Some experts believe that the movement of these fluids towards the thoracic region may be the principal component for enhanced recovery. It is thought that this action may reduce exercise-induced oedemas, increases the transfer of extracellular fluid into the bloodstream and increases cardiac output. Increased cardiac output means increased blood flow and metabolism of waste products that accumulate during exercise. The buoyancy effect of water immersion may also reduce fatigue by lowering neuromuscular signalling and improving energy conservation.

The Benefits

Cold water immersion causes hydrostatic pressure that acts in a similar manner to compression garments. It is hypothesised that compression of the underlying muscle from this pressure can squeeze blood out of the muscles aiding in circulation and removal of metabolic waste products. It is also hypothesised that cold water can also reduce core body temperature and blood flow as well as swelling from hard contact sports (e.g. combat, hard contact, and tackling). An analgesic (pain reducing) effect can also be seen from the cold temperature of the water.

Benefits seen in the literature:

• Reduction in recovery time so that an athlete can return to competition or training sooner

• Reduction in the severity and pain associated with delayed onset of muscle soreness (DOMS) 24, 48, and 96h post-exercise

• Reduced effect of rate of perceived exertion (RPE) 24h post-exercise