A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Exertional Heat Illness during Training and Competition

Exertional heat illness can affect athletes during high-intensity or long-duration exercise and result in withdrawal from activity or collapse during or soon after activity. These maladies include exercise associated muscle cramping, heat exhaustion, or exertional heatstroke. While certain individuals are more prone to collapse from exhaustion in the heat (i.e., not acclimatized, using certain medications, dehydrated, or recently ill), exertional heatstroke (EHS) can affect seemingly healthy athletes even when the environment is relatively cool. EHS is defined as a rectal temperature greater than 40 degrees C accompanied by symptoms or signs of organ system failure, most frequently central nervous system dysfunction. Early recognition and rapid cooling can reduce both the morbidity and mortality associated with EHS. The clinical changes associated with EHS can be subtle and easy to miss if coaches, medical personnel, and athletes do not maintain a high level of awareness and monitor at-risk athletes closely. Fatigue and exhaustion during exercise occur more rapidly as heat stress increases and are the most common causes of withdrawal from activity in hot conditions. When athletes collapse from exhaustion in hot conditions, the term heat exhaustion is often applied. In some cases, rectal temperature is the only discernable difference between severe heat exhaustion and EHS in on-site evaluations. Heat exhaustion will generally resolve with symptomatic care and oral fluid support. Exercise associated muscle cramping can occur with exhaustive work in any temperature range, but appears to be more prevalent in hot and humid conditions. Muscle cramping usually responds to rest and replacement of fluid and salt (sodium). Prevention strategies are essential to reducing the incidence of EHS, heat exhaustion, and exercise associated muscle cramping.

Skin manifestations of running

As the United States comes increasingly closer to being the heaviest nation on earth, many people are turning to exercise, especially running, to lose weight. Most runners, whether novice or professional, will have a skin disorder that may prompt them to seek medical attention. Although case reports and sports reviews have discussed, in a cursory fashion, the nature of these skin lesions, to our knowledge there has never been an extensive review of the literature that specifically addresses the skin diseases of runners. In this article, we present the epidemiology, origin, clinical characteristics, treatment, and prevention of skin diseases inherent to runners.

Plasma Hsp72 is higher in runners with more serious symptoms of exertional heat illness

Exertional heat illness is a potentially fatal disorder that primarily affects fit young men. Plasma Hsp72 may be important in the aetiology of this disorder, acting as a danger signal to the organism and leading to an inflammatory response. The aim of this study was to determine whether patients with exertional heat illness following a 14 km run show a difference in their plasma Hsp72 concentration compared with control subjects who completed the event without incident. Patients (n = 22) and controls (n = 7) were all male. The patients were subdivided into two groups, one of which exhibited more serious symptoms indicating neurological impairment such as confusion (n = 13) (CNS) while the other group exhibited mild symptoms (MILD) (n = 9). The CNS group had a higher rectal temperature (T(rec)) compared with the control group (41.0 +/- 0.3 vs. 39.8 +/- 0.2 degrees C, P < 0.05, mean +/- SE). Immediately after the run plasma Hsp72 was higher in the CNS group compared to controls and patients with mild symptoms (37.9, 17.0, and 20.9 ng/ml, respectively, P < 0.005). There was a correlation between plasma Hsp72 and T(rec) measured immediately after the race (r = 0.597, P < 0.001, n = 29). However, core temperature was not the only factor leading to increased plasma Hsp72 immediately post race. Plasma Hsp72 was still higher in CNS patients compared with the control group (P < 0.05) when T(rec )was included as a covariate. In conclusion, plasma Hsp72 was elevated immediately after a 14 km run with higher levels in patients with more serious symptoms of heat illness.

Heat exhaustion in The Sun-Herald City to Surf fun run

OBJECTIVE

To investigate the relationship between motivational factors and physical and biological causes of heat exhaustion in fun run entrants.

DESIGN AND SETTING

Case-control study, The Sun-Herald City to Surf fun runs in Sydney in 1991 and 1992.

PARTICIPANTS

There were 63,732 race entrants who completed the run and received a finishing time; 79 runners with heat exhaustion and 310 age, sex and performance matched controls were enrolled in the study.

MAIN OUTCOME MEASURE

A diagnosis of heat exhaustion was made if a runner collapsed and, when first receiving medical care, had a rectal temperature of 38 degrees C or higher.

RESULTS

Two readily identifiable groups of runners were at high risk of heat exhaustion--accomplished non-élite (preferred) runners and runners of good ability (Group A). The attack rate was highest among accomplished non-élite runners, but a combination of a relatively high rate and the large number of entrants in Group A runners accounted for most cases. Four major risk factors for heat exhaustion were identified: motivation to exceed previous performance targets; failure to drink fluids during the run; failure of trained runners to acclimatise for the race by training in the warmer parts of the day; and previous history of heat exhaustion.

CONCLUSION

Information from this investigation will enable more effective targeting of educational prevention programs in The Sun-Herald City to Surf fun run and provide baseline data for monitoring the effectiveness of these programs to modify high risk behaviour by participants.

Heat stroke following Rugby League football

OBJECTIVE

To present a case of severe heat stroke after Rugby League football.

CLINICAL FEATURES

A 29-year-old Rugby League forward with a mild infection of the upper respiratory tract collapsed while playing football in late March, when the ambient temperature was 24.1 degrees C and the relative humidity up to 73%. He was initially thought to have sustained a head injury and was markedly dehydrated. He suffered severe disseminated intravascular coagulation and gross neurological, renal and hepatic disturbances.

INTERVENTION AND OUTCOME

He required repeated haemodialysis, assisted ventilation and supportive therapy and remained unconscious for 10 days. He then recovered fully.

CONCLUSION

Heat stroke is potentially fatal and can be easily mistaken for head injury in contact sports. When players are dehydrated, have febrile illness and play in warm conditions, they may succumb to heat stroke.

The elite marathon runner: problems during and after competition

Two questionnaires were given to the participants of the Danish national marathon championship to obtain information on health, training habits, previous injuries and the medical problems sustained during and after the competition. All 60 participants replied to both questionnaires. The elite runner is training between 90-150 km per week, using one daily training session. He is generally careful about stretching and warming up and down. Forty-three per cent of runners sustained injuries in the last year that prevented them from training, but only 3% needed to stay off work. The most common reasons for not completing the race were exhaustion and injuries to the lower extremities. Sixty-one per cent of the runners who did not drink at all refreshment stations dropped out, whereas only 27% of those who did dropped out. There was no difference in relation to results or medical problems between the group who used a special diet before the run and those who did not. The major medical problems were gastrointestinal disturbances, skin lesions and pain or cramps in the lower extremities. No serious injuries were reported.

Distance Race Injuries: An Analysis of Runners' Perceptions

In brief: This report examines the type and frequency of self-reported injuries that occurred at the Chicago Distance Classic, a 20km race held each year in July. Questionnaires were sent to the nearly 5,000 entrants. The runners were asked about their medical history and if they had suffered injuries or illnesses from the race. Most entrants had been running two to five years. More than half stretched regularly before and after running. The knee was most often injured (10%), and the foot was second. Most orthopedic, knee, and foot injuries occurred to beginners, and most entrants were between ages 31 and 40. Many of the entrants said they were affected by the heat; 31 said they suffered severely from the heat.

Medical Complaints After a Marathon Run in Cool Weather

In brief: Little information is available about medical complaints after marathons held in cool weather. To obtain such information medical records were maintained on every runner requesting medical attention after the Bostonfest Marathon on Oct 30, 1983. One hundred sixty-four (11.5%) of the runners finishing the race requested medical attention at the finish line. Men and women requested attention with equal frequency, but younger (20 to 30 years old) and faster (finishing in less than 3:00) runners sought medical attention more often than the older and slower runners. The complaints and symptoms of runners after the race were similar to those of runners following warm-weather races.

Method of predicting the number of casualties in the Sydney City-to-Surf fun runs

A simple and effective method of predicting the number of casualties who may require urgent medical attention, which is based on previous experience in the City-to-Surf fun runs, including weather forecasts and number of entries, is described. In 1983 and 1984, the method was used to predict a number of casualties which was found to be consistent with the actual number. As a result of these predictions, the human and material resources were deployed effectively and all casualties were treated efficiently.

Exertion-induced heat exhaustion and other medical aspects of the City-to-Surf fun runs, 1978-1984

During the years 1978 to 1984, only 197 (0.14%) of 144 950 starters in a 14-km road race had suffered from heat exhaustion; of these, only three (1.5%) required admission to hospital. The effectiveness of treatment in medical centres was indicated by the fact that the mean time taken for the body temperature to fall to 38 degrees C was 31 +/- 12 minutes in all heat-exhaustion casualties, and 49 +/- 14 minutes in 41 subjects who had rectal temperatures of 42 degrees C and higher. When disaster teams from metropolitan hospitals were introduced in 1983, it became apparent that skilled staff members, despite their lack of experience in the resuscitation of combative heat casualties, could carry out the established procedures and protocols effectively and efficiently.