International Olympic Committee consensus statement on thermoregulatory and altitude challenges for high-level athletes.

Challenging environmental conditions, including heat and humidity, cold, and altitude, pose particular risks to the health of Olympic and other high-level athletes. As a further commitment to athlete safety, the International Olympic Committee (IOC) Medical Commission convened a panel of experts to review the scientific evidence base, reach consensus, and underscore practical safety guidelines and new research priorities regarding the unique environmental challenges Olympic and other international-level athletes face. For non-aquatic events, external thermal load is dependent on ambient temperature, humidity, wind speed and solar radiation, while clothing and protective gear can measurably increase thermal strain and prompt premature fatigue. In swimmers, body heat loss is the direct result of convection at a rate that is proportional to the effective water velocity around the swimmer and the temperature difference between the skin and the water. Other cold exposure and conditions, such as during Alpine skiing, biathlon and other sliding sports, facilitate body heat transfer to the environment, potentially leading to hypothermia and/or frostbite; although metabolic heat production during these activities usually increases well above the rate of body heat loss, and protective clothing and limited exposure time in certain events reduces these clinical risks as well. Most athletic events are held at altitudes that pose little to no health risks; and training exposures are typically brief and well-tolerated. While these and other environment-related threats to performance and safety can be lessened or averted by implementing a variety of individual and event preventative measures, more research and evidence-based guidelines and recommendations are needed. In the mean time, the IOC Medical Commission and International Sport Federations have implemented new guidelines and taken additional steps to mitigate risk even further.

Voluntary fluid intake and core temperature responses in adolescent tennis players: sports beverage versus water.

OBJECTIVE: To examine differences in ad libitum fluid intake, comparing a 6% carbohydrate/electrolyte drink (CHO-E) and water, and associated differences in core temperature and other selected physiological and perceptual responses in adolescent athletes during tennis training in the heat. METHODS: Fourteen healthy, fit, young tennis players (nine male; five female; mean (SD) age 15.1 (1.4) years; weight 60.6 (8.3) kg; height 172.8 (8.6) cm) completed two 120 minute tennis specific training sessions on separate days (randomised, crossover design) in a warm environment (wet bulb globe temperature: CHO-E, 79.3 (2.6) degrees F; water, 79.9 (2.2) degrees F; p>0.05). RESULTS: There were no significant differences (p>0.05) between the trials with respect to fluid intake, urine volume, fluid retention, sweat loss, perceived exertion, thirst, or gastrointestinal discomfort. However, there was a difference (p<0.05) in the percentage body weight change after training (CHO-E, -0.5 (0.7)%; water, -0.9 (0.6)%). Urine specific gravity before training (CHO-E, 1.024 (0.006); water, 1.025 (0.005)) did not correlate significantly (p>0.05) with any of these measurements or with core body temperature. In examining the main effect for trial, the CHO-E trial showed a significantly lower (p<0.001) mean body temperature (irrespective of measurement time) than the water trial. However, the mean body temperature in each trial was not associated (p>0.05) with fluid intake, fluid retention, sweat loss, or percentage body weight change. CONCLUSION: Ad libitum consumption of a CHO-E drink may be more effective than water in minimising fluid deficits and mean core temperature responses during tennis and other similar training in adolescent athletes.

Effect of hydration status on thirst, drinking, and related hormonal responses during low-intensity exercise in the heat.

During exercise-heat stress, ad libitum drinking frequently fails to match sweat output, resulting in deleterious changes in hormonal, circulatory, thermoregulatory, and psychological status. This condition, known as voluntary dehydration, is largely based on perceived thirst. To examine the role of preexercise dehydration on thirst and drinking during exercise-heat stress, 10 healthy men (21 +/- 1 yr, 57 +/- 1 ml x kg(-1) x min(-1) maximal aerobic power) performed four randomized walking trials (90 min, 5.6 km/h, 5% grade) in the heat (33 degrees C, 56% relative humidity). Trials differed in preexercise hydration status [euhydrated (Eu) or hypohydrated to -3.8 +/- 0.2% baseline body weight (Hy)] and water intake during exercise [no water (NW) or water ad libitum (W)]. Blood samples taken preexercise and immediately postexercise were analyzed for hematocrit, hemoglobin, serum aldosterone, plasma osmolality (P(osm)), plasma vasopressin (P(AVP)), and plasma renin activity (PRA). Thirst was evaluated at similar times using a subjective nine-point scale. Subjects were thirstier before (6.65 +/- 0.65) and drank more during Hy+W (1.65 +/- 0.18 liters) than Eu+W (1.59 +/- 0.41 and 0.31 +/- 0.11 liters, respectively). Postexercise measures of P(osm) and P(AVP) were significantly greater during Hy+NW and plasma volume lower [Hy+NW = -5.5 +/- 1.4% vs. Hy+W = +1.0 +/- 2.5% (P = 0.059), Eu+NW = -0.7 +/- 0.6% (P < 0.05), Eu+W = +0.5 +/- 1.6% (P < 0.05)] than all other trials. Except for thirst and drinking, however, no Hy+W values differed from Eu+NW or Eu+W values. In conclusion, dehydration preceding low-intensity exercise in the heat magnifies thirst-driven drinking during exercise-heat stress. Such changes result in similar fluid regulatory hormonal responses and comparable modifications in plasma volume regardless of preexercise hydration state.

Heat cramps: fluid and electrolyte challenges during tennis in the heat.

Sweat losses during tennis can be considerable. And while most players make a genuine effort to stay well hydrated to maintain performance and reduce the risk of heat illness, regular and copious water intake is often not enough. Besides an extraordinary water loss, extensive sweating can lead to a concomitant large electrolyte deficit too--particularly for sodium. Although a variety of other mineral deficiencies and physiological conditions are purported to cause muscle cramps, evidence suggests that, when a tennis player cramps in warm to hot weather, extensive and repeated sweating during the current and previous matches and a consequent sodium deficit are usually the primary contributing factors. Heat cramps often begin as subtle "twitches" or fasciculations in one or more voluntary muscles and, unless treated, can rapidly progress to widespread debilitating muscle spasms that leave an afflicted player on the court writhing in pain. If sufficient preventive measures are taken well before and during play, such cramping is avoidable in most cases. Appropriate and sufficient salt and fluid intake will enhance rehydration and fluid distribution throughout a player's body, so that heat cramps can be completely averted, even during long matches in the most challenging environments.

Effect of overhydration on time-trial swim performance.

The effect of hydration status on performance has not been adequately emphasized or examined in swimmers. Theoretically, moderate overhydration might reduce the proportionate fluid loss from the circulation during exercise of this nature. To explore this issue, 11 (5 women, 6 men) collegiate swimmers swam 2 183-m (200-yd) time trials (3 days apart) in alternate, randomized euhydrated (EUH) and overhydrated (OH) states. Pre-exercise plasma osmolality (EUH: 288.5 +/- 2.5 and OH: 284.6 +/- 3.3 mOsmol.kg(-1); p < 0.001), urine specific gravity (EUH: 1.022 +/- 0.003 and OH: 1.012 +/- 0.003; p < 0.001), and body weight (EUH: 72.1 +/- 9.3 and OH: 72.6 +/- 9.2 kg; p < 0.01) values distinguished the two hydration states of the swimmers. There was no difference (p > 0.05) between hydration states in postexercise plasma osmolality (EUH: 312.8 +/- 4.8 and OH: 307.2 +/- 9.9 mOsmol.kg(-1)), plasma volume (EUH: -16.5 +/- 10.0 and OH: -17.7 +/- 6.8 %Delta), plasma lactate (EUH: 18.6 +/- 3.6 and OH: 17.8 +/- 3.4 mmol.1(-1)), heart rate (EUH: 167 +/- 11 and OH: 166 +/- 16 beats.min(-1)), or perceived exertion (EUH: 16 +/- 1 and OH: 16 +/- 2) responses. Although performance time improved for 7 of the 11 swimmers during OH, there was not a statistically significant difference between the EUH (121.2 +/- 8.1 seconds) and OH (120.8 +/- 7.7 seconds) conditions. However, there was a modest bivariate correlation (r = -0.602; p < 0.05) between the change in body weight and change in performance time in going from the EUH to OH trials. These data demonstrated that overhydration provided no performance advantage for this group during a 183-m time-trial swim but emphasized the importance of adequate hydration in swim performance.

Physiological responses in tennis and running with similar oxygen uptake.

The purpose of the study was to compare selected physiological responses during singles tennis match play and continuous running at a similar mean oxygen uptake (VO2). The study consisted of two main parts, which were separated by 1 week. In the first part, 12 nationally ranked senior tennis players [six females and six males; 47.2 (6.6) years old and 47.0 (5.4) years old, respectively] each completed a 2-h singles tennis match (TE). Mean VO2 during TE [23.1 (3.1) ml.kg(-1). min(-1) for the women and 25.6 (2.8) ml.kg(-1).min(-1) for the men] was measured by a portable spirometry-telemetry system and corresponded to 56% (women) or 54% (men) of their respective maximum VO2. In the second part, the relative VO2 data measured during TE were used to set a similar workload during a 2-h treadmill run at a constant level (RU). At the measured time points, heart rate [140.1 (15.5) beats.min(-1) vs 126.4 (15.1) beats. min(-1)], lactate concentration [1.53 (0.65) mmol.l(-1) vs 1.01 (0.38) mmol.l(-1)] and glucose concentration [5.45 (0.84) mmol.l(-1) vs 4.34 (0.56) mmol.l(-1)] in capillary blood, as well as the respiratory exchange ratio [0.93 (0.03) vs 0.88 (0.03)], were higher (P<0.05) in TE compared to RU. Serum concentrations of free fatty acids increased (P < 0.05) during both work loads [from 0.25 (0.15) mmol.l(-1) to 1.31 (0.44) mmol.l(-1) in TE and from 0.22 (0.17) mmol.l(-1) to 1.24 (0.35) mmol.l(-1) in RU]. Post-exercise urine concentrations of epinephrine [0.17 (0.14) micromol.l(-1) vs 0.08 (0.04) micromol.l(-1)] and norepinephrine [1.27 (0.59) micromol.l(-1) vs. 0.55 (0.33) micromol.l(-1)] were higher in TE (P<0.05). These results indicate a stronger metabolic emphasis on glycolysis and glycogenolysis and an overall enhanced sympathoadrenal activity during tennis match play compared to continuous running exercise at a similar mean VO2.

Plasma testosterone and cortisol responses to training-intensity exercise in mild and hot environments.

Seven endurance-trained and heat-nonacclimated men (Mean+/-SEM: 20+/-1 yr; VO2max = 67+/-2 ml x kg(-1) x min(-1)) ran in two environments (M: 23 degrees C, H: 38 degrees C; 7 days apart) at two absolute training-intensity velocities (S1: 240 m x min(-1); followed by S2: 270 m x min(-1); 10 min each) during the winter months. Blood samples were taken via cannula before (pre) S1 and after S1 and S2. Plasma testosterone (TEST) concentrations increased (p<0.05) above pre levels after S1 in M (19+/-3 versus 24+/-3 nmol x L(-1)) and H (18+/-2 versus 23+/-3 nmol x L(-1)), and after S2 in H (18+/-2 versus 24+/-1 nmol x L(-1)). Plasma cortisol (CORT) and the molar ratio of TEST/CORT were unchanged from pre levels after S1 and S2 during M and H. No differences were found in plasma TEST, CORT, or the molar ratio of TEST/CORT between M and H. These results indicated that circulating levels of TEST and CORT were not changed in endurance-trained, heat-nonacclimated athletes in response to short-duration running performed at the same absolute intensity in the heat, compared to mild environmental conditions. The lack of significant differences in the molar ratio of TEST/CORT, between the 23 degrees C and 38 degrees C trials, suggested that this short-duration exercise challenge performed in the heat was no more of an anabolic or catabolic stimulus for these athletes.

Heat cramps during tennis: a case report.

A 17-year-old, nationally ranked, male tennis player (AH) had been experiencing heat cramps during tennis match play. His medical history and previous physical exams were unremarkable, and his in-office blood chemistry profiles were normal. On-court evaluation and an analysis of a 3-day dietary record revealed that AH's sweat rate was extensive (2.5 L.hr-1) and that his potential daily on-court sweat sodium losses (89.8 mmol.hr of play-1) could readily exceed his average daily intake of sodium (87.0-174.0 mmol.day-1). The combined effects of excessive and repeated fluid and sodium losses likely predisposed AH to heat cramps during play. AH was ultimately able to eliminate heat cramps during competition and training by increasing his daily dietary intake of sodium.

Fluid-electrolyte balance associated with tennis match play in a hot environment.

Twenty (12 male and 8 female) tennis players from two Division I university tennis teams performed three days of round-robin tournament play (i.e., two singles tennis matches followed by one doubles match per day) in a hot environment (32.2 +/- 1.5 degrees C and 53.9 +/- 2.4% rh at 1200 hr), so that fluid-electrolyte balance could be evaluated. During singles play, body weight percentage changes were minimal and were similar for males and females (males -1.3 +/- 0.8%, females -0.7 +/- 0.8%). Estimated daily losses (mmol.day-1) of sweat sodium (Na+) and potassium (K+) (males, Na+ 158.7, K+ 31.3; females, Na+ 86.5, K+ 18.9) were met by the players' daily dietary intakes (mmol.day-1) of these electrolytes (males, Na+ 279.1 +/- 109.4, K+ 173.5 +/- 57.7; females, Na+ 178.9 +/- 68.9, K+ 116.1 +/- 37.5). Daily plasma volume and electrolyte (Na+, K+) levels were generally conserved, although, plasma [Na+] was lower (p < .05) on the morning of Day 4. This study indicated that these athletes generally maintained overall fluid-electrolyte balance, in response to playing multiple tennis matches on 3 successive days in a hot environment, without the occurrence of heat illness.

Fluid and electrolyte losses during tennis in the heat.

A tennis player's metabolism during play in a hot environment generates an abundance of heat, which is primarily eliminated from the body by evaporation of sweat. An individual's on-court rate of fluid loss will depend on the environmental conditions, intensity of play, acclimatization, aerobic fitness, hydration status, age, and gender. Unless fluid intake closely matches sweat loss, a progressive and significant body water deficit may develop that will proportionately impair cardiovascular and thermoregulatory functions. As a result, a player can experience an increase in core temperature, premature fatigue, performance decrements, and an increased potential for heat illness. Although sweat is hypotonic compared to plasma, extended tennis play, in a hot environment, can lead to sizable Na+ and Cl- losses. Also, ad libitum drinking often leads to involuntary dehydration in these conditions. Therefore, for tennis play and training in the heat, it is important to follow a hydration plan that will minimize on-court water deficits, by optimizing fluid availability, consumption, and absorption. For tennis matches greater than 1 hour in duration, a CHO-electrolyte drink (as described earlier) is the recommended on-court beverage.

Dietary supplementation and improved anaerobic performance.

In the present study, the effects of an increased daily dose of a dietary supplement (ATP-E, 0.2 g.kg-1.day-1) on Wingate test performance were examined in 12 men (21 +/- 1.6 years) prior to and following 14 days of supplement and placebo ingestion. A double-blind and counterbalanced design was used. Results revealed higher (p < .007) preexercise blood ATP (95.4 +/- 10.5 mumol.dl-1) for the entire group following 14 days of ATP-E ingestion compared to placebo measures (87.6 +/- 10.9 mumol.dl-1). Mean power (667 +/- 73 W) was higher (p < .008) after 14 days of ATP-E ingestion versus placebo (619 +/- 67 W). Peak plasma lactate was lower (p < .07) after 14 days of ATP-E ingestion (14.9 +/- 2.8 mmol.L-1) compared to placebo (16.3 +/- 1.6 mmol.L-1). These data suggested that the improvement in 30-s Wingate test performance in this group may be related to the increased dose of ATP-E.

Urinary indices of hydration status.

Athletes and researchers could benefit from a simple and universally accepted technique to determine whether humans are well-hydrated, euhydrated, or hypohydrated. Two laboratory studies (A, B) and one field study (C) were conducted to determine if urine color (Ucol) indicates hydration status accurately and to clarify the interchangeability of Ucol, urine osmolality (Uosm), and urine specific gravity (Usg) in research. Ucol, Uosm, and Usg were not significantly correlated with plasma osmolality, plasma sodium, or hematocrit. This suggested that these hematologic measurements are not as sensitive to mild hypohydration (between days) as the selected urinary indices are. When the data from A, B, and C were combined, Ucol was strongly correlated with Usg and Uosm. It was concluded that (a) Ucol may be used in athletic/industrial settings or field studies, where close estimates of Usg or Uosm are acceptable, but should not be utilized in laboratories where greater precision and accuracy are required, and (b) Uosm and Usg may be used interchangeably to determine hydration status.

Effects of hydration state on plasma testosterone, cortisol and catecholamine concentrations before and during mild exercise at elevated temperature.

This investigation examined the influence of pre-exercise hydration status, and water intake during low intensity exercise (5.6 km.h-1 at 5% gradient) in the heat (33 degrees C), on plasma testosterone (TEST), cortisol (CORT), adrenaline (A), and noradrenaline (NA) concentrations at baseline (BL), pre-exercise (PRE), and immediately (IP), 24 h (24 P), and 48 h postexercise (48 P). Ten active men participated in four experimental treatments. These treatments differed in pre-exercise hydration status [euhydrated or hypohydrated (HY, -3.8 (SD 0.7)% body mass)] and water intake during exercise (water ad libitum or no water intake during exercise, NW). There were no significant changes in TEST, CORT, or A concentrations with time (BL, PRE, IP, 24 P, and 48 P), or among treatments. However, significant increases from BL and PRE plasma NA concentrations were observed at IP during all four treatment conditions. In addition, HY+NW resulted in significantly higher plasma NA concentrations at IP compared to all other treatments. These results suggest that moderate levels of hypohydration during prolonged, low intensity exercise in the heat do not influence plasma TEST, CORT, or A concentrations. However, plasma NA appears to respond in a sensitive manner to these hydration and exercise stresses.

Tennis: a physiological profile during match play.

Heart rate (HR), hematocrit, hemoglobin, blood glucose, and plasma concentrations of lactate, cortisol, and testosterone were monitored in 10 male subjects (Division I, 20.3 +/- 2.5 yrs, VO2max: 58.5 +/- 9.4 ml.kg-1.min-1) during singles tennis and a treadmill test. During the on-court session, HR was 144.6 +/- 13.2 beats.min-1 for the 85 min of play. Plasma lactate rose 50% from a post-warmup value of 1.6 +/- 0.6 mmol.l-1 to 2.3 +/- 1.2 mmol.l-1 during play (p greater than 0.05). Blood glucose slightly decreased (8%, p greater than 0.05) from a pre-exercise value of 4.6 +/- 0.8 mmol.l-1 as a result of the 10-min warmup. This was followed by a 23% rise (p less than 0.05) from 4.2 +/- 1.0 mmol.l-1 to 5.2 +/- 0.6 mmol.l-1, measured after the first 30 min of play. Blood glucose subsequently remained steady at slightly above the pre-exercise value. Plasma cortisol rose (9%, p greater than 0.05) during the warmup and subsequently decreased (p less than 0.05) from a post-warmup value of 558.2 +/- 285.2 nmol.l-1 to 337.1 +/- 173.3 nmol.l-1 (a 40% decrease), and remained decreased during recovery. Plasma testosterone rose 22% (p less than 0.05) from pre-exercise to recovery (13.5 +/- 3.8 nmol.l-1 and 16.5 +/- 2.6 nmol.l-1, respectively). Although tennis is characterized by periods of high-intensity exercise, the overall metabolic response resembles prolonged moderate-intensity exercise.