SODUIM: Alternatively, humans may dehydrate during exercise because they lose up to 60 mEq of Na+ for each litre of sweat (7). As a result, the equivalent of ~ 10 g of replace sweat and energy losses during exercise remain to be established. The NaCl is lost over three hours of exercise and the complete restoration of the fluid and electrolyte losses in three hours of exercise can only be achieved by the consumption of ~10 g of NaCl in food over a 24 hr period.
Drinking isotonic (280 mOsm) CHO + NaCl solutions will not adequately replace sweat Na+ losses. For the maintenance of plasma and interstitial Na+ ion concentrations and hence volumes, an athlete would have to ingest one litre of a CHO solution containing 60 mmol/l of NaCl every hour. But such a solution is unpalatable. NaCl is only palatable up to concentrations of 20 mmol/l and most athletes can only drink ~ 0.5 l/hr. Hence, whether the replacement of 10 of the ~ 60 mEq of Na+ lost in sweat per hr significantly helps to maintain plasma volume during prolonged exercise is open to debate.
POTASSIUM:Potassium is the major intracellular ion and is lost from the body in sweat and urine during exercise. However these losses are small (<1 gm even during very prolonged exercise) and are replaced by the normal daily dietary intake of 2-4 g. There is no evidence that potassium supplementation is required by the physically active
Magnesium: Magnesium is another intracellular ion that, like potassium, is lost in sweat and urine during exercise. But the losses are trivial. There is no published evidence showing that magnesium deficiency is either common amongst the physically active, or that magnesium supplementation can either increase the intracellular magnesium stores, or enhance performance.
MY COMMENT: Dr. Noakes is recognized as a pioneer in the science of dehydration and fluid replacement for endurance athletes.