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Water Replacement before, during, and after Exercise
Published in Flavia Meyer, Zbigniew Szygula, Boguslaw Wilk, Fluid Balance, Hydration, and Athletic Performance, 2016
Ronald J. Maughan, Susan M. Shirreffs
A concern with pre-exercise hyperhydration is that it may result in reductions in plasma sodium concentrations before starting exercise and therefore increase the risk of dilutional hyponatremia if large volumes of fluid are consumed during subsequent exercise (Sawka et al. 2007). Hyponatremia is further discussed below, but it should be noted that most of the reports on exercise-associated hyponatremia (EAH) did not assess pre-exercise sodium status. Where it was measured, this was most often done at the pre-race registration 2–3 days before the event rather than in the immediate pre-exercise period. While those reported cases were therefore undoubtedly associated with exercise, it is less clear that they were caused by the exercise or by behaviors specifically associated with exercise.
Effects of an Active Lifestyle on Water Balance and Water Requirements
Published in James M. Rippe, Lifestyle Medicine, 2019
Gethin H. Evans, Ronald J. Maughan, Susan M. Shirreffs
Much attention has been given to the acute and chronic effects of hypohydration, but large, acute increases in body water, though less common than hypohydration, can also be hazardous. Overhydration can occur as a result of the ingestion of water in excess of the amount needed to maintain euhydration, an electrolyte deficit, and/or an inability of the renal system to compensate for these changes by appropriate adjustments of renal function. As with chronic hypohydration, chronic overhydration is unlikely to lead to serious health consequences in healthy individuals, but occasionally it can be fatal. If the concentration of sodium in the extracellular space falls, water moves from the interstitial space into the cellular compartment, leading to swelling of cells. In most tissues this is of little consequence, though it may have implications for a number of cellular functions.69 If sufficiently severe, however, an increase in intracranial pressure will result and symptoms associated with “water intoxication,” including headache, nausea, confusion, and changes in behavior. If intracranial pressure continues to increase, this can lead to central nervous system dysfunction, coma, and death. Exercise-associated hyponatremia, brought about by ingesting a greater volume of water than is lost via sweat, has been associated with several deaths and was reported in 13% of finishers of the Boston marathon in 2002 despite these individuals showing no clinical symptoms.70 A number of non-exercise cases of “water intoxication,” brought on due to excessive fluid ingestion, have also been described. These include cases from fraternity initiation practices, co-ingestion of large volumes of fluid with recreational drugs such as MDMA, water ingestion during weight loss plans, and social competitions involving large volumes of fluid intake.71
Altitude, temperature, circadian rhythms and exercise
Published in Adam P. Sharples, James P. Morton, Henning Wackerhage, Molecular Exercise Physiology, 2022
Henning Wackerhage, Kenneth A. Dyar, Martin Schönfelder
In relation to exercise in the heat, sweating and the resultant fluid loss and dehydration are key reactions and issues. Humans have ≈4 million exocrine sweat glands. Sweat generates heat loss as 2.5 kJ are required to transfer 1 g of water to water vapour at 35°C (41). Of these sweat glands, 90% are the smaller eccrine glands and the remainder are larger apocrine glands (48). Why do we sweat and how does the resultant loss of water (dehydration) and salts/ions affect our performance? During exercise, the whole body sweat rate differs greatly in between humans. In a hot environment, we typically lose between 0.5 and 2 L of sweat per hour but in ≈2% of athletes this can reach more than 3 L per hour with extremes of nearly 6 L of sweat lost per hour (49). To counteract this, the ACSM recommends drinking enough to prevent a loss of more of 2% body weight loss from water deficit and to avoid excessive changes in the electrolyte balance (50). During sweating, water losses are not the only issue as sweat contains salts and sodium (Na+) is a key one. The saltiness of our sweat differs between individuals, with Na+ concentrations ranging from 10 to 90 mmol/L (49). Thus, the harder and longer we exercise in high temperatures, and the more we are genetically predisposed to lose water and Na+, the more we will dehydrate and become hyponatraemic, and this will affect our exercise performance (50). Exercise-associated hyponatremia refers to blood Na+ concentrations below 135 mmol/L and is a health hazard that can lead to death. It typically occurs when athletes drink too much hypotonic, Na+-low fluids such as water so that Na+-losses through sweating and urine exceed the Na+-intake. Depending on the severity, hyponatremia can cause major health issues and it is likely that it was responsible for the death of several athletes (51).
Proteinuria in a high-altitude 161-km (100-mile) ultramarathon
Published in The Physician and Sportsmedicine, 2021
Morteza Khodaee, Anahita Saeedi, Bjørn Irion, Jack Spittler, Martin D. Hoffman
Those runners with post-race proteinuria were demonstrated to have a higher serum CK than those without post-race proteinuria. This is not unexpected, as this relationship was previously demonstrated [14]. Noteworthy is that some have considered a CK greater than 20,000 U/L as an appropriate threshold for treatment to prevent renal failure from rhabdomyolysis [36,37]. With a mean serum CK over 26,000 U/L among the group with post-race proteinuria, this urine marker seems to represent an inexpensive and rapid field measure for assessment of those athletes who might be at some risk for acute kidney injury. Noting that those with post-race proteinuria also had darker urine color, a simple color analysis may offer similar clinical utility. On the other hand, urine may be dark and concentrated due to arginine vasopressin secretion in association with exercise-associated hyponatremia and overhydration, so one should perform a clinical assessment with this in mind before encouraging oral fluid intake [38,39].