Health and Fitness March 08
by Dr Rod Edwards PhD
r.edwards@griffith.edu.au
School of Education and Professional Studies, Griffith University
Water requirements and Exercise in the Heat.
For most of the year, South East Queensland is quite hot and humid and we need to be sensible in our own activity and in organised sport to protect us from heat and dehydration problems.
How does the body deal with the heat?
Water requirements and Exercise in the Heat.
For most of the year, South East Queensland is quite hot and humid and we need to be sensible in our own activity and in organised sport to protect us from heat and dehydration problems.
How does the body deal with the heat?
The brain registers that our core temperature is rising
Circulation moves more to the skin (hence the redness)
Water passes from the blood to the outside of the skin through sweat glands
The water (hopefully, if it is not too humid) evaporates, thus cooling the skin and the blood just below the surface.
This blood then cools the rest of the body
We then need to replace that water.
Note that this mechanism will not be good enough if it is too hot or humid or both. If the core temperature of the body exceeds 40 degrees (37 degrees is normal), the risk of heat injury is very real.
Wet Bulb Globe Temperature (WBGT).
This is different to dry or ambient temperature as it takes humidity, radiation and wind movement into account and all sporting organisers should have a WBGT thermometer available. Sports Medicine Australia says that moderate to heavy exercise in WBGT of more than 28 degrees presents considerable risk.
How much water to drink?
Research suggests that, for an adult, at least 600 mls should be taken in the two hours before exercise and then (depending on sweating), about 250 mls every 15 to 20 minutes during activity.
What about children?
Children sweat later and less than adults as the sweat glands that create body odour do not start operating until puberty. Thus, they may not be able to cool down as well.
Sports Medicine Australia, in its “Preventing Heat Illness in Sport” Policy states:
“Events and activities involving children and adolescents that are conducted or scheduled for times likely to present conditions where the ambient (dry) air temperature is greater than or equal to 34 degrees Celsius, should be postponed or cancelled.” P.4
What to drink?
Water is still the best, although there is some evidence that sports drinks (less than 8% sugar) may be useful. Soft drinks and sweet cordial (greater than 8% sugar) should be avoided. Water should be cool, not iced.
For more information, go to the Sports Medicine Australia website: www.sma.org.au
Circulation moves more to the skin (hence the redness)
Water passes from the blood to the outside of the skin through sweat glands
The water (hopefully, if it is not too humid) evaporates, thus cooling the skin and the blood just below the surface.
This blood then cools the rest of the body
We then need to replace that water.
Note that this mechanism will not be good enough if it is too hot or humid or both. If the core temperature of the body exceeds 40 degrees (37 degrees is normal), the risk of heat injury is very real.
Wet Bulb Globe Temperature (WBGT).
This is different to dry or ambient temperature as it takes humidity, radiation and wind movement into account and all sporting organisers should have a WBGT thermometer available. Sports Medicine Australia says that moderate to heavy exercise in WBGT of more than 28 degrees presents considerable risk.
How much water to drink?
Research suggests that, for an adult, at least 600 mls should be taken in the two hours before exercise and then (depending on sweating), about 250 mls every 15 to 20 minutes during activity.
What about children?
Children sweat later and less than adults as the sweat glands that create body odour do not start operating until puberty. Thus, they may not be able to cool down as well.
Sports Medicine Australia, in its “Preventing Heat Illness in Sport” Policy states:
“Events and activities involving children and adolescents that are conducted or scheduled for times likely to present conditions where the ambient (dry) air temperature is greater than or equal to 34 degrees Celsius, should be postponed or cancelled.” P.4
What to drink?
Water is still the best, although there is some evidence that sports drinks (less than 8% sugar) may be useful. Soft drinks and sweet cordial (greater than 8% sugar) should be avoided. Water should be cool, not iced.
For more information, go to the Sports Medicine Australia website: www.sma.org.au
