Effects of dehydration on exercise performance.
ABSTRACT Dehydration refers both to hypohydration (dehydration induced prior to exercise) and to exercise-induced dehydration (dehydration that develops during exercise). The latter reduces aerobic endurance performance and results in increased body temperature, heart rate, perceived exertion, and possibly increased reliance on carbohydrate as a fuel source. Although the negative effects of exercise-induced dehydration on exercise performance were clearly demonstrated in the 1940s, athletes continued to believe for years thereafter that fluid intake was not beneficial. More recently, negative effects on performance have been demonstrated with modest (<2%) dehydration, and these effects are exacerbated when the exercise is performed in a hot environment. The effects of hypohydration may vary, depending on whether it is induced through diuretics or sauna exposure, which substantially reduce plasma volume, or prior exercise, which has much less impact on plasma volume. Hypohydration reduces aerobic endurance, but its effects on muscle strength and endurance are not consistent and require further study.
Full-textDOI: · Available from: Susan I Barr, Jul 07, 2015
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ABSTRACT: Maintaining a proper fluid balance is important during exercise as athletes are prone to develop dehydration during exercise. Although several factors may regulate the fluid balance, little is known about the role of sex during prolonged moderate-intensity exercise. Therefore, we compared body mass changes and fluid balance parameters in men vs women in a large heterogeneous group of participants during prolonged exercise. Ninety-eight volunteers walked 30-50 km at a self-selected pace. Exercise duration (8 h, 32 min) and intensity (69% HR(max) ) were comparable between groups. Men demonstrated a significantly larger change in body mass than women (-1.6% vs -0.9%, respectively, P < 0.001) and a higher incidence of dehydration (defined as ≥2% body mass loss) compared with women (34% vs 12%, respectively, odds ratio = 4.2, 95% CI = 1.1-16.7). Changes in blood sodium levels were significantly different between men (+1.5 mmol/L) and women (-0.4 mmol/L), while 27% of the men vs 0% of the women showed postexercise hypernatremia (sodium levels ≥ 145 mmol/L). Moreover, men demonstrated a significantly lower fluid intake (2.9 mL/kg/h) and higher fluid loss (5.0 mL/kg/h) compared with women (3.7 and 4.8 mL/kg/h, respectively). Taken together, our data suggest that men and women demonstrate different changes in fluid balance in response to a similar bout of exercise.Scandinavian Journal of Medicine and Science in Sports 08/2011; 23(2). DOI:10.1111/j.1600-0838.2011.01371.x · 3.17 Impact Factor
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ABSTRACT: Voluntary dehydration is a condition where humans do not drink appropriately in the presence of an adequate fluid supply. This may adversely affect their physical and intellectual performance. The present study aimed to describe the prevalence of voluntary dehydration among elementary school children of different ethnicities and countries of birth. Four hundred and twenty-nine elementary school children, aged 8-10 years, from four subpopulations (Israeli-born Jewish and Bedouin-Arab children, and immigrant children who recently arrived to Israel from Eastern Europe and from Ethiopia) were studied. The level of dehydration was determined by noontime urine osmolality, from samples taken over 1 week in mid-summer. Urine osmolality <500 mOsmol kg(-1) H(2)O was considered to be an appropriate level of hydration. Mean urine osmolality was 862 +/- 211 mOsmol kg(-1) H(2)O. Osmolality above 800 mOsmol kg(-1) H(2)O was detected in 67.5% of the urine samples; among these, 25% were above 1000 mOsmol kg(-1) H(2)O. The most dehydrated group was that of Israeli-born Jewish children, whereas the Bedouin-Arab children were the least dehydrated. A high proportion of children who reside in a hot and arid environment were found to be in a state of moderate to severe dehydration. Bedouin ethnicity was associated with better hydration, whereas Israeli-born Jews were most severely dehydrated. Educational intervention programmes promoting water intake should start in early childhood and continue throughout life.Journal of Human Nutrition and Dietetics 05/2009; 22(5):455-60. DOI:10.1111/j.1365-277X.2009.00960.x · 2.07 Impact Factor
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ABSTRACT: In this review the effects of diurnal fasting on normal physiological processes are considered. Ramadan is placed in a circadian context, food and fluid ingestion being displaced to the pre-sunrise and post-sunset hours. Over the holy month, negative energy balance is often experienced, though this deficit is not a universal finding. Responses to exercise during the day show influences consistent with hypohydration and an increased reliance on fat as a source of fuel for exercise. Muscle performance and psychomotor performance are impaired as the month of fasting progresses but it is not clear how circadian rhythms in responses to activity are altered. For some measures at rest there is a reduction in amplitude and a delay in acrophase. Health-related benefits are reflected in a rise in high-density lipoprotein cholesterol and individuals with predispositions for coronary heart disease are not at increased risk of cardiovascular disorders due to fasting. The physiological adjustments during the month have some similarities to the disturbances in circadian rhythms experienced in different circumstances. The Ramadan model provides an alternative to those for ageing, nocturnal shift-work and time-zone transitions in understanding the links between behaviour and endogenous circadian rhythms.Physiology & Behavior 03/2007; 90(2-3):219-28. DOI:10.1016/j.physbeh.2006.09.004 · 3.03 Impact Factor