Phil Watson

Exercise, heat, hydration and the brain.

The performance of both physical and mental tasks can be adversely affected by heat and by dehydration. There are well-recognized effects of heat and hydration status on the cardiovascular and thermoregulatory systems that can account for the decreased performance and increased sensation of effort that are experienced in the heat. Provision of fluids of appropriate composition in appropriate amounts can prevent dehydration and can greatly reduce the adverse effects of heat stress. There is growing evidence that the effects of high ambient temperature and dehydration on exercise performance may be mediated by effects on the central nervous system. This seems to involve serotonergic and dopaminergic functions. Recent evidence suggests that the integrity of the blood brain barrier may be compromised by combined heat stress and dehydration, and this may play a role in limiting performance in the heat.

The brain and fatigue : New opportunities for nutritional interventions?

Abstract It is clear that the cause of fatigue is complex, influenced by events occurring in both the periphery and the central nervous system. Work conducted over the last 20 years has focused on the role of brain serotonin and catecholamines in the development of fatigue, and the possibility that manipulation of neurotransmitter precursors may delay the onset of fatigue. While there is some evidence that branched-chain amino acid and tyrosine ingestion can influence perceived exertion and some measures of mental performance, the results of several apparently well-controlled laboratory studies have not demonstrated a positive effect on exercise capacity or performance under temperate conditions. As football is highly reliant upon the successful execution of motor skills and tactics, the possibility that amino acid ingestion may help to attenuate a loss in cognitive function during the later stages of a game would be desirable, even in the absence of no apparent benefit to physical performance. There are several reports of enhanced performance of high-intensity intermittent exercise with carbohydrate ingestion, but at present it is difficult to separate the peripheral effects from any potential impact on the central nervous system. The possibility that changes in central neurotransmission play a role in the aetiology of fatigue when exercise is performed in high ambient temperatures has recently been examined, although the significance of this in relation to the pattern of activity associated with football has yet to be determined.

Heat and cold : what does the environment do to the marathon runner?

The marathon poses a considerable physical challenge for athletes of all levels. When combined with high heat and humidity, not only is performance potentially compromised, but health and well-being are also at risk. There are well recognised effects of heat and hydration status on the cardiovascular and thermoregulatory systems that can account for the decreased performance and increased sensation of effort that are experienced when competing in the heat. Elevated exercise heart rate and core temperature at the same absolute exercise intensity are commonly reported. Dehydration occurring during exercise in the heat and results in reductions in stroke volume, cardiac output and blood pressure, as well as a marked decline in blood flow to the working muscles. Recent work suggests that hyperthermia may have a direct affect on the CNS and the brain may contribute to fatigue during prolonged exercise in a warm environment. At present, evidence supports a significant role of catecholaminergic neurotransmission, but there are a number of metabolic and circulatory perturbations occurring within the brain that may also be important in the fatigue process.

Nutrition, the brain and prolonged exercise

Abstract Possible peripheral mechanisms of fatigue have been widely documented, including the depletion of muscle glycogen and the loss of body fluids. The notion that the brain may be intimately involved in the fatigue process is not a new one, but recently possible neurobiological mechanisms involved in this response have been investigated. Changes in central neurotransmission occur during exercise that may result in feelings of tiredness, lethargy, and a loss of motivation to continue exercise, contributing to the development of fatigue. There is evidence that manipulation of the neurotransmitters serotonin, dopamine, and noradrenaline, through the administration of pharmacological agents, may delay the onset of fatigue during prolonged exercise, particularly when performing in a warm environment. Supplementation with branched-chain amino acids and tyrosine can influence perceived exertion and some measures of mental performance, but the results of several apparently well-controlled laboratory studies have not demonstrated a positive effect on exercise capacity under temperate conditions. The ergogenic effects of carbohydrate and caffeine are well documented, but often little attention is paid to the central effects of these nutrients. Carbohydrate ingestion has been demonstrated to alter brain activity and cerebral metabolism, factors that may be important in the development of fatigue and the maintenance of skill performance. There is strong evidence for a positive effect of caffeine on exercise performance, with recent data highlighting the role of central adenosine as a mediator of this response.

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.

Mild hypohydration increases the frequency of driver errors during a prolonged, monotonous driving task (Abstract, 2nd International and 4th Spanish Hydration Conference)

Purpose: Driver error is the largest cause of road traffic accidents, accounting for around 68 % of all vehicle crashes in the UK. During long and monotonous driving, most individuals display progressive signs of visual fatigue and a loss of vigilance. Since deficits in total body water (TBW) are associated with altered mood and decrements in aspects of cognitive function, it is possible that dehydrated drivers may be more susceptible to errors in judgement and car handling. With this in mind, the aim of the present study was to examine the effects of fluid restriction, on performance during a prolonged, monotonous driving task. Methods: Eleven healthy males (age 22 ± 4 y) completed a familiarisation trial, before two experimental trials were undertaken in a randomised manner. Each experimental trial took place over two days. On day 1 volunteers were instructed to consume a volume of fluid in line with published guidelines (HYD trial) or 25 % of this intake (FR trial). Participants came to the laboratory the following morning after an overnight fast (day 2). One hour following a standard breakfast, a 120 min driving simulation task began. During the HYD trial volunteers were provided with 200 mL of fluid every hour, and on the FR trial only 25 mL was made available each hour. Body mass, serum and urine osmolality, and subjective feelings were recorded during trials. Driver errors, including instances of lane drifting or late breaking, brain activity (EEG) and heart rate were recorded throughout the driving task. Results: Pre-trial body mass (P=0.692), urine osmolality (P=0.838) and serum osmolality (P=0.574) were the same on both trials. FR resulted in a 1.1±0.7 % reduction in body mass, compared to -0.1±0.6 % in the HYD trial (P = 0.002). Urine and serum osmolality were both increased following FR (P Conclusions: The results of the present study suggest that mild hypohydration, resulted in an increase in errors during a prolonged, monotonous drive, compared to that observed while performing the same task in a hydrated condition. The magnitude of decrement reported was similar to that observed following the ingestion of alcohol resulting in a blood alcohol content of approximately 0.08 % (the current UK legal driving limit), or while sleep deprived. There is no question that both drink-driving and driving while tired increases the risk of road traffic accidents, and many countries have instigated national campaigns to educate drivers of the associated risks. Given the present fin- dings, perhaps some attention should also be directed to encouraging appropriate hydration practices among drivers. Key words: Dehydration, Cognitive function, Road traffic accident Language: en

Systematic examination of the influence of carbohydrate supplementation on physical and mental performance in warm conditions

Exercise performance in the heat is not limited by the availability of carbohydrate (CHO), and the provision of more dilute CHO-electrolyte solutions may confer a greater benefit during prolonged exercise in a warm environment. The present study evaluated the effects of low concentrations of CHO on physical and mental performance. Twelve healthy males (mean±SD Age 21±2 years; Height 179±8 cm; Mass 80.2±7.1 kg; VO2max 4.2±0.5 l/min) exercised to volitional exhaustion at a workload corresponding to 60% VO2max at 30°C, 60% RH. Subjects ingested 3 ml/kg body mass of a 0%, 2%, 4% or 6% CHO solution before exercise and a further 1.5 ml/kg body mass of the appropriate solution every 10 min during exercise. Heart rate, core temperature, RPE and perceived thermal stress were recorded at regular intervals. Expired gas samples were collected to determine rates of substrate utilisation. Cognitive function was assessed using a computerised test battery. Exercise time to exhaustion was 94.5±24.5 min, 104.1±20.1 min, 105.5±26.7 min and 112.0±28.7 min in the 0%, 2%, 4% and 6% trials respectively (P=0.046). Drink CHO content did not influence heart rate (P=0.464) or core temperature (P=0.516). Rates of CHO (P=0.105) and fat (P=0.339) oxidation were not influenced by the drink ingested. The exercise bout resulted in a slowing of response times to a visual search task in the 0% and 2% trials (p<0.05). The present data demonstrate a positive relationship between drink CHO content and exercise time to exhaustion. There was some suggestion that CHO may attenuate decrements in motor skills tasks performed after exhausting exercise. The study was carried out in relation to the product Powerade and was funded in part by The Coca-Cola Company.

Influence of fluid ingestion and carbohydrate supplementation on physical and mental performance during intermittent high-intensity exercise

Carbohydrate (CHO) ingestion results in positive effects on exercise capacity, repeated sprint speed and sport-specific skill performance during intermittent exercise. This study evaluated the effects of lower concentrations of CHO on performance during intermittent exercise. Ten healthy males (mean±SD age 25±3 years; height 1.75±0.06 m; mass 75.9±6.4 kg; VO2max 54.2±5.0 ml/kg/min) completed four 15-min periods of intermittent running, consisting of maximal sprinting interspersed with periods of running and walking (Loughborough Intermittent Shuttle Test). This was followed by the multistage shuttle-running fitness test (MSFT) to volitional exhaustion. Subjects consumed 3 ml/kg body mass of plain water, a 3% CHO solution or a 6% CHO solution before exercise and a further 1.5 ml/kg body mass of the appropriate drink after each 15-min block. A trial with no fluid ingestion was also completed. Sprint time, heart rate, core temperature, perceived exertion and thermal stress were recorded at regular intervals. Cognitive function was assessed using a computer-based test battery. Time to exhaustion in the MSFT was 9.9±2.0 min, 10.2±2.0 min, 10.9±1.9 min and 11.2±1.8 min in the no fluid, water, 3% and 6% CHO trials, respectively (p=0.004). Core temperature reached 38.9±0.4°C during the no fluid trial, 38.5±0.4°C in the water trial and 38.6±0.3°C at the end of the CHO trials (p=0.011). There was no change in response times to a visual search task in the no fluid and water trials, but CHO ingestion improved response times after exercise (3% CHO, p=0.036; 6% CHO, p=0.041). These data suggest that drinks containing lower CHO concentrations can produce improvements in exercise capacity and motor response times similar to those observed with the ingestion of the amounts of CHO found in many sports drinks. The study was carried out in relation to the product Powerade and was funded in part by The Coca-Cola Company.