Dopamine/noradrenaline reuptake inhibition in women improves endurance exercise performance in the heat.

Catecholamine reuptake inhibition improves the performance of male volunteers exercising in warm conditions, but sex differences in thermoregulation, circulating hormones, and central neurotransmission may alter this response. With local ethics committee approval, nine physically active women (mean ± SD age 21 ± 2 years; height 1.68 ± 0.08 m; body mass 64.1 ± 6.0 kg; VO2peak 51 ± 7 mL/kg/min) were recruited to examine the effect of pre-exercise administration of Bupropion (BUP; 4 × 150 mg) on prolonged exercise performance in a warm environment. Participants completed a VO2peak test, two familiarization trials, and two randomized, double-blind experimental trials. All trials took place during the first 10 days of the follicular phase of the menstrual cycle. Participants cycled for 1 h at 60% VO2peak followed by a 30-min performance test. Total work done was greater during the BUP trial (291 ± 48 kJ) than the placebo trial (269 ± 46 kJ, P = 0.042, d = 0.497). At the end of the performance test, core temperature was higher on the BUP trial (39.5 ± 0.4 °C) than on the placebo trial (39.2 ± 0.6 °C, P = 0.021; d = 0.588), as was heart rate (185 ± 9 vs 179 ± 13, P = 0.043; d = 0.537). The results indicate that during the follicular phase of the menstrual cycle, an acute dosing protocol of BUP can improve self-regulated performance in warm conditions.

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.

Hydration and performance during Ramadan.

In the absence of any food or fluid intake during the hours of daylight during the month of Ramadan, a progressive loss of body water will occur over the course of each day, though these losses can be completely replaced each night. Large body water deficits will impair both physical and cognitive performance. The point at which water loss will begin to affect performance is not well defined, but it may be as little as 1-2% of body mass. For resting individuals in a temperate environment, the water loss that occurs during a day without food or fluid will typically amount to about 1% of body mass by the time of sunset. This small loss of body water is unlikely to have a major adverse effect on any aspect of physical or cognitive performance. Larger body water losses will occur, however, in hot weather or if exercise is undertaken. Performance in events lasting about 1 hour or longer may be impaired in the absence of fluid intake during the event. In weight-category sports, there may be difficulties due to the impossibility of restoring body water content between the weigh-in and competition, and athletes will require alternative strategies. Where more than one competition or training session takes place in a single day and where substantial fluid losses are incurred, recovery will be impaired by the absence of fluid intake.

Dietary supplements for athletes: emerging trends and recurring themes.

Dietary supplements are widely used at all levels of sport. Changes in patterns of supplement use are taking place against a background of changes in the regulatory framework that governs the manufacture and distribution of supplements in the major markets. Market regulation is complicated by the increasing popularity of Internet sales. The need for quality control of products to ensure they contain the listed ingredients in the stated amount and to ensure the absence of potentially harmful substances is recognized. This latter category includes compounds prohibited under anti-doping regulations. Several certification programmes now provide testing facilities for manufacturers of both raw ingredients and end products to ensure the absence of prohibited substances. Athletes should carry out a cost-benefit analysis for any supplement they propose to use. For most supplements, the evidence is weak, or even completely absent. A few supplements, including caffeine, creatine, and bicarbonate, are supported by a strong research base. Difficulties arise when new evidence appears to support novel supplements: in recent years, ß-alanine has become popular, and the use of nitrate and arginine is growing. Athletes seldom wait until there is convincing evidence of efficacy or of safety, but caution is necessary to minimize risk.

Distance running in hot environments: a thermal challenge to the elite runner.

Endurance performance is impaired in the heat, and a combination of high temperature and high humidity presents a major challenge to the elite marathon runner, who must sustain a high metabolic rate throughout the race. The optimum temperature for marathon performance is generally about 10-12 °C. The optimum temperature may be lower for faster runners than for slower runners. Sweat evaporation limits the rise in core temperature, but dehydration will impair cardiovascular function, leading to a fall in blood flow to muscle, skin and other tissues. There is growing evidence that the effects of high ambient temperature and dehydration on performance of exercise may be mediated by effects on the central nervous system. This seems to involve serotonergic and dopaminergic functions.

Dehydration and rehydration in competative sport.

Dehydration, if sufficiently severe, impairs both physical and mental performance, and performance decrements are greater in hot environments and in long-lasting exercise. Athletes should begin exercise well hydrated and should drink during exercise to limit water and salt deficits. Many athletes are dehydrated to some degree when they begin exercise. During exercise, most drink less than their sweat losses, some drink too much and a few develop hyponatraemia. Athletes should learn to assess their hydration needs and develop a personalized hydration strategy that takes account of exercise, environment and individual needs. Pre-exercise hydration status can be assessed from urine frequency and volume, with additional information from urine color, specific gravity or osmolality. Changes in hydration status during exercise can be estimated from the change in body mass: sweat rate can be estimated if fluid intake and urinary losses are also measured. Sweat salt losses can be determined by collection and analysis of sweat samples. An appropriate, individualized drinking strategy will take account of pre-exercise hydration status and of fluid, electrolyte and substrate needs before, during and after a period of exercise.

Development of hydration strategies to optimize performance for athletes in high-intensity sports and in sports with repeated intense efforts.

Hypohydration - if sufficiently severe - adversely affects athletic performance and poses a risk to health. Strength and power events are generally less affected than endurance events, but performance in team sports that involve repeated intense efforts will be impaired. Mild hypohydration is not harmful, but many athletes begin exercise already hypohydrated. Athletes are encouraged to begin exercise well hydrated and - where opportunities exist - to consume fluid during exercise to limit water and salt deficits. In high-intensity efforts, there is no need, and may be no opportunity, to drink during competition. Most team sports players do not drink enough to match sweat losses, but some drink too much and a few may develop hyponatremia because of excessive fluid intake. Athletes should assess their hydration status and develop a personalized hydration strategy that takes account of exercise, environment and individual needs. Pre-exercise hydration status can be assessed from urine markers. Short-term changes in hydration can be estimated from the change in body mass. Sweat salt losses can be determined by collection and analysis of sweat samples. An appropriate drinking strategy will take account of pre-exercise hydration status and of fluid, electrolyte and substrate needs before, during and after exercise.

Living, training and playing in the heat: challenges to the football player and strategies for coping with environmental extremes.

Dehydration and hyperthermia both, if sufficiently severe, will impair exercise performance. Dehydration can also impair performance of tasks requiring cognition and skill. Body temperature may exceed 40 °C in competitive games played in hot weather, but limited data are available. Football played in the heat, therefore, poses a challenge, and effects on some aspects of performance become apparent as environmental temperature increases above about 12-15 °C. Prior acclimatization will reduce the impact of high environmental temperatures but provides limited protection when humidity is also high. Ingestion of fluids is effective in limiting the detrimental effects on performance: drinks with added carbohydrate and electrolytes are generally more effective than plain water and drinks may be more effective if taken cold than if taken at ambient temperature. Pre-exercise lowering of body temperature may aid some aspects of performance, but the efficacy has not been demonstrated in football.

Hydration and sweating responses to hot-weather football competition.

During a football match played in warm (34.3 ± 0.6 °C), humid (64 ± 2% rh) conditions, 22 male players had their pre-match hydration status, body mass change, sweat loss and drinking behavior assessed. Pre-match urine specific gravity (1.012 ± 0.006) suggested that all but three players commenced the match euhydrated. Players lost 3.1 ± 0.6 L of sweat and 45 ± 9 mmol of sodium during the 90-min match and replaced 55 ± 19% of their sweat losses and hence by the end of the game were 2.2 ± 0.9% lighter. The water volume consumed during the game was highly variable (1653 ± 487 mL; 741-2387 mL) but there was a stronger relationship between the estimated pre-game hydration status and water volume consumed, than between sweat rate and water volume consumed. In a second match, with the same players 2 weeks later in 34.4 ± 0.6 °C, 65 ± 3% rh, 11 players had a sports drink available to them before and during the match in addition to water. Total drink volume consumed during the match was the same, but approximately half the volume was consumed as sports drink. The results indicate that substantial sweat water and electrolyte losses can occur during match play in hot conditions and a substantial water and sodium deficit can occur in many players even when water or sports drink is freely available.

Effect of hot environmental conditions on physical activity patterns and temperature response of football players.

Heat stress may contribute to decreased match performance when football is played in extreme heat. This study evaluated activity patterns and thermal responses of players during soccer matches played in different environmental conditions. Non-acclimatized soccer players (n=11, 20±2 years) played two matches in conditions of moderate heat (MH) and high heat (HH) index. Core temperature (T(c) ) and physical performance were measured using a telemetric sensor and a global positioning system, respectively. The average ambient temperature and relative humidity were MH 34±1 °C and 38±2%; HH 36±0 °C and 61±1%. Peak T(c) in the MH match was 39.1±0.4 °C and in the HH match it was 39.6±0.3 °C. The total distance covered in the first and second halves was 4386±367 and 4227±292 m for the MH match and 4301±487 and 3761±358 m for the HH match. Players covered more distance (P<0.001) in the first half of the HH match than in the second half. In football matches played at high environmental temperature and humidity, the physical performance of the players may decrease due to high thermal stress.

Fasting and sport: an introduction.

Most humans observe an overnight fast on a daily basis, and the human body copes well with short duration fasting. Periodic fasting is widely practised for cultural, religious or health reasons. Fasting may take many different forms. Prolonged restriction of food and fluid is harmful to health and performance, and it is often automatically assumed that intermittent fasting will lead to decrements in exercise performance. Athletes who choose to fast during training or competitions may therefore be at a disadvantage. The available evidence does not entirely support this view, but there is little or no information on the effects on elite athletes competing in challenging environments. Prolonged periods of training in the fasted state may not allow optimum adaptation of muscles and other tissues. Further research on a wide range of athletes with special nutrition needs is urgently required. In events where performance might be affected, other strategies to eliminate or minimise any effects must be sought.

The effects of fasting on metabolism and performance.

An overnight fast of 8-10 h is normal for most people. Fasting is characterised by a coordinated set of metabolic changes designed to spare carbohydrate and increase reliance on fat as a substrate for energy supply. As well as sparing the limited endogenous carbohydrate, and increased rate of gluconeogenesis from amino acids, glycerol and ketone bodies help maintain the supply of carbohydrate. Many individuals undergo periodic fasts for health, religious or cultural reasons. Ramadan fasting, involving 1 month of abstention from food and fluid intake during daylight hours, is practised by a large part of the world population. This period involves a shift in the pattern of intake from daytime to the hours of darkness. There seems to be little effect on overall daily dietary intake and only small metabolic effects, but there may be implications for both physical and cognitive function. The limited evidence suggests that effects of Ramadan-style fasting on exercise performance are generally small. This needs to be balanced, however, against the observation that small differences in performance are critical in determining the outcomes of sporting events. Studies involving challenging sporting events (prolonged sustained or intermittent high-intensity events, hot and humid environments) are needed. Increases in subjective sensations of fatigue may be the result of loss of sleep or disruption of normal sleep patterns. Modifications to the competition timetable may minimise or even eliminate any effect on performance in sport, but there may be negative effects on performance in some events.

A comparison of water turnover in older people in community and institutional settings.

BACKGROUND: Maintaining water balance is essential for health, but environmental factors, pathology and the ageing process can adversely affect water homeostasis. OBJECTIVE: This study examined the relationship between physical dependency and daily water turnover rate in an older population. DESIGN: Daily water turnover (DWT) was estimated, using deuterium oxide ((2)H(2)O) as a tracer for water, over two separate 7-day periods in summer and winter in two older populations. The independent group (N = 22) lived in their own homes and were self-caring. The dependent group (N = 15) lived in institutional care, and were more physically dependent. None of the subjects had significant mental impairment. Total body water (TBW) and DWT were estimated from the equilibration concentration of ingested (2)H(2)O and its subsequent elimination rate. RESULTS: The independent group had a median (range) age of 75(69-88) y, a mean Barthel Index (BI) of 19.8, and a mean Abbreviated Mental Test (AMT) score of 9.8. The dependent group were older (83(72-93) y), with a mean BI of 13 and a mean AMT of 9.3. Average median (range) DWT in the independent group was similar in summer (2.2(1.3-3.6) l.d(-1)) and winter (2.1(1.4-3.6) l.d(-1)), but faster than in the dependent group (1.5(0.9-2.9) and 1.6(1.0-2.8) l.d(-1), respectively) during the same two periods. Median urine output in the independent group was similar in summer (1.7(0.8-3.3) l.d(-1)) and winter (1.7(0.9-3.2) l.d(-1)), but greater than in the dependent group (1.1(0.6-2.7) and 0.9(0.5-1.6) l.d(-1), respectively). CONCLUSION: These results show that the water turnover rate of many older people is low, and that intake may be affected especially in those with physical disability.

The limits of human athletic performance.

For each individual, there is a limit to the capacity to perform exercise. The limitation, however, depends on the nature of the task and is also influenced by a number of other factors. Muscle strength is determined largely by muscle mass, specifically muscle cross-sectional area, but is also influenced by neural drive and biomechanical factors. Endurance performance depends on both cardiovascular capacity and the metabolic characteristics of the skeletal muscles. These factors are determined in part by genetic endowment: the elite sprinter has a high proportion of Type 2 muscle fibres while the leg muscles of the successful marathon runner are composes mainly of Type 1 fibres. Whatever the genetic potential, expression of this depends on the intensity, duration and frequency of the applied training stimulus, diet and other factors. The limitation may also depend on environmental factors, such as altitude and temperature.

Executive summary and conclusions from the European Hydration Institute Expert Conference on human hydration, health, and performance.

On April 7-8, 2014, the European Hydration Institute hosted a small group of experts at Castle Combe Manor House, United Kingdom, to discuss a range of issues related to human hydration, health, and performance. The meeting included 18 recognized experts who brought a wealth of experience and knowledge to the topics under review. Eight selected topics were addressed, with the key issues being briefly presented before an in-depth discussion. Presented here is the executive summary and conclusions from this meeting.

Total and subcutaneous adipose tissue in women: the measurement of distribution and accurate prediction of quantity by using magnetic resonance imaging.

Total and subcutaneous adipose tissue in seven lean and seven obese women were quantified using magnetic resonance imaging (MRI). The distributions of adipose tissues along the body were closely correlated: subcutaneous with total, both within and between lean and obese groups. Lean women had proportionally less adipose tissue in the lower thorax and upper abdomen than did obese women. Reducing the number of MRI scans from 17 to 4 did not increase the residual SD of predicted body adipose tissue (2.9 percent) when body density was used as the reference measure. MRI gave an estimate of total-body adipose tissue significantly closer to the value for fat percent produced when the results from five other techniques (skinfold thickness, underwater weighing, 40K whole-body counting, isotopic water dilution, and tetrapolar bioelectrical impedance) were averaged than when any other technique was used alone. MRI-determined percent body adipose tissue in women is close to, and proportional to, estimates derived by underwater weighing.