Most nutritional supplements require fairly closely difined concentration, often balanced with complementary vitamins and minerals, to provie optimum performance. Relatively small change in the body’s water content can easily upset those balances and lead to less than optimal performance.
One of the major roles of water during exercise is to aid cooling and maintain body temperature in the narrow band of efficient operating temperature. A key procedure in the cooling system is the evaporation of sweat from skin. This water is lost to the system and there is a limited amount water that can be released for this purpose before the efficiency of other operations is sacrificed.
The rate of sweat loss depends on a number of aspect, including the environment and the intensity of exercise. Whilst warm temperature can increase sweat rates, high humidity can reduce the rate of evaporation and hence restrict the cooling effect. It may be surprising to many that winter training can result in similarly high water losses. Not only is water lost through breathing, but also in the micro environment created by the more protective clothing that is worn. Typically, outside training requires a windproof jacket or top. As exercise increases body temperature, the air under jacket increases the need to cool. The increase in humidity, restricts the evaporation, demanding a further increase in cooling, and hence more sweating. All this leads to greater water loss.
The third component of this situation is core body temperature. As intensity of exercise increases, so too does core temperature, and the need to sweat. This leads to dehydration which, result in an increase in body temperature and so on.
Lose fluid – lose performance
Although typical sweat rates are in the region of 1 litre per hour, athletes have often been recorded as losing as much as 2 litres of fluid in an hour. This equates to a 2 kg per hour weight-loss. Research has shown that performance car drop off by 20% when fluid loss reaches 2% of total body weight. In practical terms, a 60 kg runner need only a mere 1,2 litres of sweat. In adverse conditions this can be reached in the first 90 minutes of exercise! So how do you combat this?
There are basically two remedies :
- make sure that you adopt a re-hydration programme that will keep your fluid levels topped up.
- Use a water-loading technique to provide a larger starting base before exercise.
The fact is that in competitive situations it is highly unlikely that fluid levels can be maintained throughout a long event. Research has shown that, even with the recommended 250-300ml per 30 minutes of exercise, it is unlikely that the fluid can be absorbed at a rate that equates with the rate of loss. In practice however, it has been found that most runners perceive that they are drinking more than they actually are. The voluntary drinking rate tends to be closer to 500-800ml per hour. This compounds the risk of performance loss and de-hydration. Thus long, intense exercise will lead to a degree of dehydration for most people. Partial dehydration automatically result in a reduction in exercise intensity.
By means of contract, it is worth making the point that cyclists do not experience the same reduction in voluntary drinking rate, not do those who exercise at low intensity. There have been several cases of slower ultra marathon runners suffering from ‘hyper hydration’ in races of 50km and longer. It is speculated that these runners may also tend to have been inappropriately trained for the event, and thus in a stage of extreme fatigue for the latter section of the event. Runner who have difficulty in passing urine during exercise are also susceptible. As these slower runner tire they tend to spend more time at refreshment tables and use drinking of fluid as a reason to delay their progress. This lead to excessive fluid intake. Ironically, the symptoms can often be mistaken for dehydration, and there have been cases of drips being applied by the medical staff at the end of the event. Thankfully this condition has received greater awareness to work done in south Africa, primarily by professor Tim Noakes and the team at university of Capetown.
For most, however, the threat to performance comes from dehydration. Whilst hot fluid is obviously not desirable, it has been shown recently that there is little difference in absorption rate between warm and cold fluid. The main benefit of cool drinks is taste and cooling effect. By comparison, if too cold, drinks can have side effects like headaches and stoach cramps.
Sip it!
The best absorption rates are obtained by taking small amounts of fluid on a regular basis. In other words, sipping 100ml of fluid every 10minutes, is better than taking on board 300ml at the end of each half hour.
Although it is useful to have such definitive figures, these are of little use when actually execising, as few carry a measuring jug with them. A simple guide however can be obtained by converting amounts into mouthfuls.
By taking a mouthful of fluid a bottle or cup whilst running an then spitting that into a measuring jug, you will get an idea of how much each swallow of fluid accounts for. In this way it is possible to keep a better track of just how much you are taking on board.
Continue to Easy ways to optimize fluid intake -2
by norrie Williamson