nosh magazine (issue 5) - Page 6

nosh magazine HYDRATION AND PERFORMANCE Sports Dieititians Australia explains the importance of hydration for performance. ater is essential for the human body. It is required to maintain blood volume, regulate body temperature and allow muscle contractions to take place. During exercise, the body maintains its optimal body temperature through sweating. Heat is removed from the body when beads of sweat on the skin evaporate, which results in a loss of body fluid. Sweat production (and therefore fluid loss) increases with a rise in ambient temperature and humidity, as well as with an increase in exercise intensity. So while sweat loss during exercise is essential for body temperature regulation, it can lead to dehydration. W As dehydration increases, there is a gradual reduction in physical and mental performance. There is an increase in heart rate and body temperature, and an increased perception of how hard the exercise feels, especially when exercising in the heat. Impaired skill level can also occur, along with mental fatigue. Studies show that loss of fluid equal to two per cent of body mass is sufficient to cause a detectable decrease in performance (that’s a 1.4kg loss in a 70kg athlete). Dehydration of greater than two per cent loss of body weight increases the risk of nausea, vomiting, diarrhoea and other gastro-intestinal problems during and after exercise. Dehydration also reduces the rate of fluid absorption from the intestines, making it more difficult to reverse the fluid deficit. You may end up feeling bloated and sick if you delay fluid replacement. It is impossible to ‘train’ or ‘toughen’ your body to handle dehydration. Can you drink too much? Drinking more fluid than is comfortable (in any conditions) has the potential to interfere with your performance. In cool weather or when the exercise pace is gentle, the rate of sweat loss may be quite low. It is unnecessary and potentially dangerous to drink at rates that are far greater than sweat losses. Over-hydration during exercise is called hyponatraemia (dilute levels of sodium in the bloodstream). Symptoms include headaches, disorientation, coma, and in severe cases, death. It is important to note though that this is relatively rare and dehydration is a much more common issue for athletes. Estimating your fluid loss Knowing your sweat rate can give you an indication of how much you should be drinking during exercise. Sports dietitians routinely measure an athlete’s sweat rate during training and competition in a range of environmental conditions, to provide them with the information required to design an individual fluid plan. A simple strategy to work out your individual fluid loss is as follows: • Weigh yourself in minimal clothing, as close to the start of exercise as possible. Ideally you should empty your bladder Sports Dietitians Australia (SDA) Learn more at: website To find out more about dehydration and sport, check out the full fact sheet online at Or to find an Accredited Sports Dietitian click here. 6 before weighing. • Commence exercise session. • Weigh yourself at the end of your session, again in minimal clothing, ensuring you towel off any excess sweat from your body, pass urine and void your bowels if necessary. • Your weight change during exercise reflects your total fluid loss (i.e. the difference between your sweat losses and fluid intake). Other minor losses come from breathing, spitting, vomiting and other insignificant sources. • Repeat this procedure under different training conditions to get a good understanding of your individual fluid needs, for example in hot versus cold temperatures, high versus low intensity sessions. • Remember that weight loss during exercise is primarily water loss (not fat loss), and needs to be replaced soon after finishing exercise. In summary • Aim to match your sweat rate and fluid loss with fluid intake as closely as possible. • Get to know your fluid loss by weighing yourself before and after training sessions and competition. • Ensure that you drink at a rate that is comfortable. • Practice your competition fluid intake plan in training sessions. • Water is an excellent fluid for low intensity and short duration sports. • Sports drinks are ideally suited to high intensity and endurance sports. • Drink alcohol sensibly and assess the detrimental effects on your recovery. N