How long should you cool; is a 2 second ice-bath or a bottle of cold water over your head effective?
In cooling during exercise, a distinction is made between:
- subjective sensation of coolness
- actual reduction in core temperature.
The sensation of coolness is mainly determined by cooling the skin, as skin thermo-receptors respond directly to temperature drops. The experience of ‘nice and cool’ is subjective and can occur without any significant change in core temperature. Short, local cooling such as cold towels, ice bags or cold water on the skin often quickly provide a sensation of coolness, while hardly affecting core temperature.
Core temperature is effectively lowered only when sufficient heat is removed from the body, by applying sufficient cooling power and enough time. This requires a combination of surface cooling and effective blood flow to transport heat from the deep tissues to the skin.
There is evidence that the perception of temperature can be independent of changes in core temperature. Athletes can experience thermal comfort (sensation of cooling) without a decrease in core temperature. This is attributed to factors such as skin temperature and psychological effects. (*62)
The length required to achieve considerable core temperature reduction was studied. Hand ánd forearm immersion in water was used to reduce core temperature. But, time was required. Hand immersion of both hands ánd forearm for 20 minutes in water of 20°C (68°F) resulted in a core temperature reduction of 1.2°C (2.2°F). Starting at 38.5°C (101.3°F), after 20 minutes the core temperature decreased to 37.3°C (99.1°F). (*16)
From this study we learn 3 things:
- Prolonged cooling time is essential
- The cooling-load does not have to be extremely cold
- Enough cooling power/volume is required.
Talking about sensation; menthol sprayed on a jersey in a 16.1-km cycling time trial did not improve performance time. *19
It is very natural that endurance sporters search for heat relief, also in mediate temperature conditions. Cold water, ice, a sponge, they all fulfill temporary sensory relief and perceived cooling that indeed can help endurance athletes mentally and physically cope with heat for a short moment. But it does not help at all to lower core temperature significantly.