Never Mind the Bullocks, Here's the Science by Karl Kruszelnicki Page A
Authors: Karl Kruszelnicki
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11.46 kcal/min.
Assume that this heat energy is dissipated by evaporating sweat (which is close to 100% water).
The Latent Heat of Evaporation of water = 2.43 kJ/g = 0.58 kcal/g.
So a sweating person who generates 800 watts of waste heat needs to evaporate about 20 g of water/sweat each minute. This works out to about 1,200 g/hr, or 1.2 litres per hour.
Sports and Stress
The effect that different sports have upon the body ranges from relatively non-stressful (such as lawn bowls or billiards) to very stressful (such as marathon running).
How stressful? Consider a person with a fever so excessively high that it is almost lethal. Their metabolism can increase by 100% above normal. But medium-distance runners can increase their metabolism by 2,000% above normal—and survive. Some sports, if continued for too long, can be lethal if they interfere too much with your electrolyte levels, or cause hyperthermia (extremely high body temperature).
What You Need
You need sugar if you burn lots of energy and electrolytes if you have lost some via sweating. This is because sweat removes mainly sodium from your body.
Depending on the sport, there are four possibilities with regard to sugar and electrolytes. You will need (1) sugar and electrolytes; or (2) just sugars; or (3) just electrolytes; or (4) neither sugar nor electrolytes.
In the first situation, a person needing both sugar and electrolytes might be a marathon runner, who will burn energy and sweat a lot. Marathon runners, American Football players and male competition tennis players can sweat fluids at over 2 litres/hr.
In the second situation, a person needing mainly extra sugar might play a so-called intermittent sport in cold weather. They stop and start a lot, and so burn up energy, but might not sweat a lot. Depending on the position played, this could be someone in amateur soccer or tennis. Mind you, ‘serious’ amateurs could pushthemselves hard and sweat a lot, and so be shifted up to the first category of needing both sugar and electrolytes.
A person in the third category—who would need only electrolytes (and water, of course)—might be an athlete sweating in a sauna, in order to keep their weight down to a class limit. This can be dangerous if the person takes the dehydration too far—and is not recommended.
People who go for a 10 minute jog around the park every morning fall into the fourth category. They would not really need any extra sugar or electrolytes, just H 2 O. On the other hand, they might enjoy the taste of the sports drink (even though it’s more expensive than petrol, volume for volume).
Advantages of Sports Drinks
Sports physiologists agree that some athletes in prolonged exhaustive sports definitely need a combination of sugars and salts. Sports drinks also help athletes engaged in moderate to intense activity of an hour or more. Athletes also hydrate better with a sports drink—they tend to consume more, and the water is better absorbed. And if the athlete is low on energy before the start of the event, the carbohydrates in the sports drink can help maintain the glucose levels in the blood better. And, surprisingly, just having the taste of sugars in the mouth can make athletes perform better.
Test cricketers can get dehydrated after a hot day of intermittent activity, mostly spent standing on the cricket field. Surprisingly, there have been cases where the cricketers did not rehydrate overnight, and so began the next day on the cricket field already slightly dehydrated. Sports drinks could help here.
Sports physiologists also agree that drinking pure water does not flush away electrolytes, and that most people who exercise for less than an hour do not need sports drinks.
Rinse Mouth to Perform Better!
It seems perfectly reasonable that you can improve your sports performance by consuming some fuel (e.g. sugars). But, strangely, it also seems that you get the same effect from simply rinsing it around your mouth, and then spitting it
Assume that this heat energy is dissipated by evaporating sweat (which is close to 100% water).
The Latent Heat of Evaporation of water = 2.43 kJ/g = 0.58 kcal/g.
So a sweating person who generates 800 watts of waste heat needs to evaporate about 20 g of water/sweat each minute. This works out to about 1,200 g/hr, or 1.2 litres per hour.
Sports and Stress
The effect that different sports have upon the body ranges from relatively non-stressful (such as lawn bowls or billiards) to very stressful (such as marathon running).
How stressful? Consider a person with a fever so excessively high that it is almost lethal. Their metabolism can increase by 100% above normal. But medium-distance runners can increase their metabolism by 2,000% above normal—and survive. Some sports, if continued for too long, can be lethal if they interfere too much with your electrolyte levels, or cause hyperthermia (extremely high body temperature).
What You Need
You need sugar if you burn lots of energy and electrolytes if you have lost some via sweating. This is because sweat removes mainly sodium from your body.
Depending on the sport, there are four possibilities with regard to sugar and electrolytes. You will need (1) sugar and electrolytes; or (2) just sugars; or (3) just electrolytes; or (4) neither sugar nor electrolytes.
In the first situation, a person needing both sugar and electrolytes might be a marathon runner, who will burn energy and sweat a lot. Marathon runners, American Football players and male competition tennis players can sweat fluids at over 2 litres/hr.
In the second situation, a person needing mainly extra sugar might play a so-called intermittent sport in cold weather. They stop and start a lot, and so burn up energy, but might not sweat a lot. Depending on the position played, this could be someone in amateur soccer or tennis. Mind you, ‘serious’ amateurs could pushthemselves hard and sweat a lot, and so be shifted up to the first category of needing both sugar and electrolytes.
A person in the third category—who would need only electrolytes (and water, of course)—might be an athlete sweating in a sauna, in order to keep their weight down to a class limit. This can be dangerous if the person takes the dehydration too far—and is not recommended.
People who go for a 10 minute jog around the park every morning fall into the fourth category. They would not really need any extra sugar or electrolytes, just H 2 O. On the other hand, they might enjoy the taste of the sports drink (even though it’s more expensive than petrol, volume for volume).
Advantages of Sports Drinks
Sports physiologists agree that some athletes in prolonged exhaustive sports definitely need a combination of sugars and salts. Sports drinks also help athletes engaged in moderate to intense activity of an hour or more. Athletes also hydrate better with a sports drink—they tend to consume more, and the water is better absorbed. And if the athlete is low on energy before the start of the event, the carbohydrates in the sports drink can help maintain the glucose levels in the blood better. And, surprisingly, just having the taste of sugars in the mouth can make athletes perform better.
Test cricketers can get dehydrated after a hot day of intermittent activity, mostly spent standing on the cricket field. Surprisingly, there have been cases where the cricketers did not rehydrate overnight, and so began the next day on the cricket field already slightly dehydrated. Sports drinks could help here.
Sports physiologists also agree that drinking pure water does not flush away electrolytes, and that most people who exercise for less than an hour do not need sports drinks.
Rinse Mouth to Perform Better!
It seems perfectly reasonable that you can improve your sports performance by consuming some fuel (e.g. sugars). But, strangely, it also seems that you get the same effect from simply rinsing it around your mouth, and then spitting it
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