Fluid ingestion

Fluid ingestion pre-exercise, during and post exercise

When we perform physical work our bodies produce heat as a waste product. We can also gain heat from the environment around us. The human body only operates at a +/- 2 degrees Celcius tolerance level at the core so it has to constantly manage temperature through the hyper thalamus located in the brain. It is this area that 'turns on' our sweat response, attempts to move heat from the core to the surface and dilates blood vessels in our skin. It also causes us to feel thirsty and so seek to drink fluids. However, our thirst response is very poor and out of step with the actual needs of the body. Often, when we feel thirsty we are already suffering some degree of de-hydration. The very real danger of losing too much fluid from our body is that we suffer heat stroke which can lead to death (and has in sports people of many sorts). In most cases though the danger in not taking on fluids at the right time, and of the right sort, is a fall in performance levels through fatigue induced by the low levels of fluid and essential electrolytes such as sodium.

Much research has been carried out into the recommended levels of hydration that differing types of physical activity demand, how best to ensure a hydrated state exists during the activity and the importance of carrying on this hydration regime after the activity has ended. The following is a summary of some of that research (much of it gained from the Gatorade Sports Science Exchange) as it affects karate as an activity estimated to be 75-80% anaerobic and 20-25% aerobic with intermittent bouts of exercise.

Ensure that a fully hydrated state exists prior to the activity taking place by cutting down on caffeine drinks some hours before practice (they act as diuretics and increase fluid lost through urination). Imbibe approx. 450ml of fluid in the two hours prior to practice of a fluid/carbohydrate/sodium drink where the carbohydrate is no more than 6% of the total and the sodium is just a pinch.

During exercise:
Aim to drink about 150-300ml of this fluid every 15-20 minutes of heavy exercise (remember don't wait until you feel thirsty to drink). If possible try to cool your drink down as this passes through the intestinal wall quicker than warmed fluid.

Post exercise:
Continue with your rehydration regime with 450ml of your chosen fluid (above) per pound of body weight lost during the activity. Spread this fluid intake over the first 2 hours or so after exercise cessation to compensate for fluid lost in urination.

Your chosen fluid replacement:
Experiment with various fluids until you find one that you like the taste of, has the correct % of carbohydrate and that you can take in the required quantities. This may be a proprietary 'sports drink', plain water or a mixture of your choosing I prefer to take 1 liter of orange juice and dilute it 1:1 with bottled water. The Tesco variety of juice has the right % of carbohydrates in it when diluted and is cheap at less than 40p a carton!

So you don't think YOU are at risk of heat stroke?
The risk from heat isn't just a factor of the environmental heat outside. Karateka, in particular, need to take account of the ambient temperature inside the dojo as well as any humidity measures as well. The combination of environmental temp. and the relative humidity arrives at an 'apparent temp.' that the body actually feels. For instance, when the environmental temp. is around 80F and the relative humidity at 70% the 'real' effect on the body is 85F. As these factors increase (and this may not always be at similar rates) the effect on the body alters. At 85F and 70% humidity the effect is 93F and the athlete is at risk of heat stroke. For a fuller guide refer to the Heat Index visit the Gatorade site. Heat stroke kills. Make sure you know the signs and symptoms and how to react to it in another. You could be their only chance if they slip into unconsciousness.

The science bit for those who need some persuasion:
Gisolfi et al (1992) suggested that fluid absorption through the intestinal tract was most rapid in solutions containing 6% carbohydrate of any sort in the drink. At an 8% solution the type of carbohydrate made a difference with glucose slowing down absorption.

Murray et al (1991) conducted research into the effects of carbohydrate feeding during exercise and found that performance improved significantly during steady state prolonged exercise. In a 1989 article Murray et al also suggested that a 6% fructose solution impaired performance as it caused gastrointestinal distress and a greater loss of plasma volume.

Mitchell et al (1988) determined that in tests looking at the levels of carbohydrate feeding (%'s) that solutions between 5 and 7.5% carbohydrate improved performance and encouraged gastric emptying at the same rate as plain water.

Ivy et al (1988) looked at carbohydrate feeding following performance and determined that carbohydrate drinks consumed immediately after and up to 2 hours exercise improved muscle glycogen storage for the next bout of exercise maybe later in the day. This is important for those who have multiple work outs each day.

Shirreffs et al (1996) took the above research one step further and suggested that consumption of 150% of the body mass lost to dehydration was the optimal amount to consume post exercise. e.g. if you lose 1lb of weight you need to consume 24 oz of fluid. 200% worked just as well but less than 100% failed to restore body levels as urine production was counter productive to this aim.

The full list of references can be found by visiting the Gatorade web site - Fluids 2000, Fluids and performance Research where much information as to the efficacy of Gatorade also appears.

As a final word on this interesting topic you may like to view the simple to use pyramid illustration below.

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All information on this ASKO website is 2000-2004 Blackrock Karate Club.
Last updated on Friday, August 13th, 2004.