Fluid balance for optimal performance

Fundamental Concepts of Human Thermoregulation and Adaptation to Heat: A Review in the Context of Global Warming

The international community has recognized global warming as an impending catastrophe that poses significant threat to life on earth. In response, the signatories of the Paris Agreement (2015) have committed to limit the increase in global mean temperature to < 1.5 °C from pre-industry period, which is defined as 1950-1890. Considering that the protection of human life is a central focus in the Paris Agreement, the naturally endowed properties of the human body to protect itself from environmental extremes should form the core of an integrated and multifaceted solution against global warming. Scholars believe that heat and thermoregulation played important roles in the evolution of life and continue to be a central mechanism that allows humans to explore, labor and live in extreme conditions. However, the international effort against global warming has focused primarily on protecting the environment and on the reduction of greenhouse gases by changing human behavior, industrial practices and government policies, with limited consideration given to the nature and design of the human thermoregulatory system. Global warming is projected to challenge the limits of human thermoregulation, which can be enhanced by complementing innate human thermo-plasticity with the appropriate behavioral changes and technological innovations. Therefore, the primary aim of this review is to discuss the fundamental concepts and physiology of human thermoregulation as the underlying bases for human adaptation to global warming. Potential strategies to extend human tolerance against environmental heat through behavioral adaptations and technological innovations will also be discussed. An important behavioral adaptation postulated by this review is that sleep/wake cycles would gravitate towards a sub-nocturnal pattern, especially for outdoor activities, to avoid the heat in the day. Technologically, the current concept of air conditioning the space in the room would likely steer towards the concept of targeted body surface cooling. The current review was conducted using materials that were derived from PubMed search engine and the personal library of the author. The PubMed search was conducted using combinations of keywords that are related to the theme and topics in the respective sections of the review. The final set of articles selected were considered "state of the art," based on their contributions to the strength of scientific evidence and novelty in the domain knowledge on human thermoregulation and global warming.

Nutritional knowledge and attitudes of adolescent swimmers in trinidad and tobago

Purpose. To investigate the level of nutrition knowledge and attitude of adolescent male and female swimmers training competitively in Trinidad and Tobago. Methodology. A self-administered questionnaire, which consisted of 21 nutrition knowledge and 11 attitude statements, was utilized to assess the level of nutrition knowledge and attitude of adolescent swimmers. For the assessment of nutrition knowledge, correct answers were given a score of “1” and incorrect answers were given a score of “0.” For the evaluation of attitude towards nutrition, a score ranging from 1 to 5 was assigned to each response; “5” was given to the most positive response, and “1” was given to the most negative. Data were analyzed using SPSS version 21.0. Results. Two hundred and twenty swimmers with a mean age of 14.56 ± 2.544 completed the questionnaire. The mean nutrition knowledge score was 10.97 ± 2.897 and mean attitude score was 41.69 ± 6.215. Nutrition knowledge was positively and significantly related to the number of reported nutrition sources (r = 0.172, P = 0.005). Nutrition knowledge was positively and significantly related to the attitude (r = 0.130, P = 0.027). Conclusions and Implication. Athletes lack nutrition knowledge but have a positive attitude towards nutrition, which may indicate receptiveness to future nutrition education.

Human Thermoregulation and Measurement of Body Temperature in Exercise and Clinical Settings

This review discusses human thermoregulation during exercise and the measurement of body temperature in clinical and exercise settings. The thermoregulatory mechanisms play important roles in maintaining physiological homeostasis during rest and physical exercise. Physical exertion poses a challenge to thermoregulation by causing a substantial increase in metabolic heat production. However, within a non-thermolytic range, the thermoregulatory mechanisms are capable of adapting to sustain physiological functions under these conditions. The central nervous system may also rely on hyperthermia to protect the body from “overheating.” Hyperthermia may serve as a self-limiting signal that triggers central inhibition of exercise performance when a temperature threshold is achieved. Exposure to sub-lethal heat stress may also confer tolerance against higher doses of heat stress by inducing the production of heat shock proteins, which protect cells against the thermolytic effects of heat. Advances in body temperature measurement also contribute to research in thermoregulation. Current evidence supports the use of oral temperature measurement in the clinical setting, although it may not be as convenient as tympanic temperature measurement using the infrared temperature scanner. Rectal and oesophagus temperatures are widely accepted surrogate measurements of core temperature (Tc), but they cause discomfort and are less likely to be accepted by users. Gastrointestinal temperature measurement using the ingestible temperature sensor provides an acceptable level of accuracy as a surrogate measure of Tc without causing discomfort to the user. This form of Tc measurement also allows Tc to be measured continuously in the field and has gained wider acceptance in the last decade. Key words: Core temperature, Gastrointestinal temperature, Ingestible temperature sensor, Thermoregulation

Drinking guidelines for exercise: what evidence is there that athletes should drink "as much as tolerable", "to replace the weight lost during exercise" or "ad libitum"?

The most recent (1996) drinking guidelines of the American College of Sports Medicine (ACSM) propose that athletes should drink "as much as tolerable" during exercise. Since some individuals can tolerate rates of free water ingestion that exceed their rates of free water loss during exercise, this advice has caused some to overdrink leading to water retention, weight gain and, in a few, death from exercise-associated hyponatraemic encephalopathy. The new drinking guidelines of the International Olympic Committee (IOC), recently re-published in this Journal, continue to argue that athletes must drink enough to replace all their weight lost during exercise and to ingest sodium chloride since sodium is "the electrolyte most critical to performance and health". In this rebuttal to that Consensus Document, I argue that these new guidelines, like their predecessors, lack an adequate, scientifically proven evidence base. Nor have they been properly evaluated in appropriately controlled, randomized, prospective clinical trials. In particular, these new guidelines provide erroneous recommendations on five topics. If novel universal guidelines for fluid ingestion during exercise are to be promulgated by important international bodies including the IOC, they should first be properly evaluated in appropriately controlled, randomized, prospective clinical trials conducted under environmental and other conditions that match those found in "out-of-doors" exercise. This, and the potential influence of commercial interests on scientific independence and objectivity, are the two most important lessons to be learned from the premature adoption of those 1996 ACSM drinking guidelines that are not evidence-based. These concerns need to be addressed before the novel IOC guidelines are accepted uncritically. Otherwise the predictable consequences of the premature adoption of the 1996 ACSM guidelines will be repeated.

Weight changes, medical complications, and performance during an Ironman triathlon

BACKGROUND

Subjects exercising without fluid ingestion in desert heat terminated exercise when the total loss in body weight exceeded 7%. It is not known if athletes competing in cooler conditions with free access to fluid terminate exercise at similar levels of weight loss.

OBJECTIVES

To determine any associations between percentage weight losses during a 224 km Ironman triathlon, serum sodium concentrations and rectal temperatures after the race, and prevalence of medical diagnoses.

METHODS

Athletes competing in the 2000 and 2001 South African Ironman triathlon were weighed on the day of registration and again immediately before and immediately after the race. Blood pressure and serum sodium concentrations were measured at registration and immediately after the race. Rectal temperatures were also measured after the race, at which time all athletes were medically examined. Athletes were assigned to one of three groups according to percentage weight loss during the race.

RESULTS

Body weight was significantly (p<0.0001) reduced after the race in all three groups. Serum sodium concentrations were significantly (p<0.001) higher in athletes with the greatest percentage weight loss. Rectal temperatures were the same in all groups, with only a weak inverse association between temperature and percentage weight loss. There were no significant differences in diagnostic indices of high weight loss or incidence of medical diagnoses between groups.

CONCLUSIONS

Large changes in body weight during a triathlon were not associated with a greater prevalence of medical complications or higher rectal temperatures but were associated with higher serum sodium concentrations.

Management of fluid and hydration in patients with acute subarachnoid haemorrhage - an action research project

BACKGROUND

The contemporary role of the nurse in managing fluid and hydration in patients is currently ill-defined. Considering the pivotal function nurses have in the delivery of fluid therapies, and the high priority such therapies have in the successful treatment and prevention of secondary brain injury in subarachnoid haemorrhage, the clarification of this role is essential.

AIMS AND OBJECTIVES

This research aims to clarify the nurse's role in fluid therapies in relation to subarachnoid haemorrhage. The objectives were to determine how nurses presently see their role in relation to fluid management in patients with subarachnoid haemorrhage, to determine the cues to guide their practice, and how this role corresponds to current patient care. A final objective was to identify how the nurse's role can be maximized to provide optimal patient care.

METHODOLOGICAL DESIGN

This project takes an action research approach to examining the nurse's role in the care of patients with subarachnoid haemorrhage. A combination of focus groups, physiological data, nursing and medical documentation and a review of recent literature were used to meet the aims and objectives of the project.

RESULTS

The results illustrate that, while nurses involved in the study are knowledgeable about fluid and hydration in subarachnoid haemorrhage, they have an ambiguity surrounding their role. Improvements can be made in the quality of patient care through educational sessions for staff and clarification of medical and nursing interdisciplinary roles.

CONCLUSION

This action research project has gone a considerable distance towards begin clarifying this role, and has illustrated clearly that the nurse's role is pivotal to the successful implementation of such treatments. With further education and collaboration with the interdisciplinary team the nurses' role can be expanded to provide optimal, and dynamic patient-centred care.

RELEVANCE TO CLINICAL PRACTICE

The results of this study highlight gaps within contemporary nursing and medical approaches to patients with subarachnoid haemorrhage, highlighting areas for improvement. It also begins to clarify the role of the nurse, with evidence of the cues they use to guide their practice.

Effects of changes in water compartments on physiology and metabolism

There is paramount evidence to suggest the importance of cell volume changes for the regulation of cell function, including protein metabolism. Among many other effects, cell swelling inhibits proteolysis and stimulates protein synthesis. However, most of the data pertinent to this theory relate to in vitro experiments. This paper reviews the evidence about the relevance of cell swelling and changes in water compartments to regulation of metabolism at the whole body level in animals and humans. Protein metabolism is most likely regulated by cellular hydration in health and disease. Cellular hydration appears to bear no effect on energy metabolism. The relationship between cellular hydration and lipolysis deserves to be verified. There appears to be a possible weak effect on glucose metabolism. Further studies are therefore necessary to challenge the cell swelling theory. If confirmed, strategies to modify cellular hydration could be used to improve metabolic orientations especially in the critically ill.

Hydration effects on physiological strain of horses during exercise-heat stress

This study examined the effects of hyperhydration, exercise-induced dehydration, and oral fluid replacement on physiological strain of horses during exercise-heat stress. On three occasions, six horses completed a 90-min exercise protocol (50% maximal O2 uptake, 34.5 degrees C, 48% relative humidity) divided into two 45-min periods (exercise I and exercise II) with a 15-min recovery between exercise bouts. In random order, horses received no fluid (NF), 10 liters of water (W), or a carbohydrate-electrolyte solution (CE) 2 h before exercise and between exercise bouts. Compared with NF, preexercise hyperhydration (W and CE) did not alter heart rate, cardiac output (Q), stroke volume (SV), core body temperature, sweating rate (SR), or sweating sensitivity during exercise I. In contrast, after exercise II, exercise-induced dehydration in NF (decrease in body mass: NF, 5.6 +/- 0.8%; W, 1.1 +/- 0.4%; CE, 1.0 +/- 0.2%) resulted in greater heat storage, with core body temperature approximately 1. 0 degrees C higher compared with W and CE. In exercise II, the greater thermal strain in NF was associated with significant (P < 0. 05) decreases in Q (10 +/- 2%), SV (9 +/- 3%), SR, and sweating sensitivity. We concluded that 1) preexercise hyperhydration provided no thermoregulatory advantage; 2) maintenance of euhydration by oral fluid replacement ( approximately 85% of sweat fluid loss) during exercise in the heat was reflected in higher Q, SV, and SR with decreased heat storage; and 3) W or an isotonic CE solution was equally effective in reducing physiological strain associated with exercise-induced dehydration and heat stress.