Work in the Heat as Affected by Intake of Water, Salt and Glucose

Abstract

The performance of physical work in the heat can be affected for better or worse by a variety of factors, the most important being physical fitness and acclimatization, nutritional state, clothing and drugs. This paper deals with the effects of water, salt and glucose, with principal emphasis upon the attainment of the best possible performance. The effects of water soluble vitamins will be mentioned briefly. The present material will be restricted in two ways. First,. attention will be confined to performance of fixed tasks by fully acclimatized men working intermittently in moist or in dry heat. Therefore, the results are applicable to steel workers, miners and soldiers in tlhe desert, all of whom usually do a day's work in the heat and spend the rest of the time in cooler surroundings. Second, we shall consider only the immediate hour to hour effects of the above dietary factors upon men n-hose overall daily intake was always adequate in water, salt, carbohydrate and vitamins. There will be no consideration of prolonged deficiency or excess from day to day. METHODS. Experiments were performed in the late fall or winter in a heated room under hot dry (100 F., 30 per cent relative humidity) and hot moist conditions (95 F. and 90 F., 83 per cent relative humidity). Six healthy young men, fully acclimatized as judged by the criteria of Robinson and colleagues (1943), marched at least three times a week at 3.5 m.p.h. up grades which will be specified in the tables. Depending upon the severity of the temperature and humidity, which were const,ant in individual series of experiments, they marched anywhere from one to six hours with a ten minute rest in each hour. Certain measurements were made periodically in every experiment. These were: a, environmental temperature and humidity with a sling psychrometer; 6, pulse rate by palpation; c, rectal t#emperature with a calibrated clinical thermometer; d, sweating by net change in nude body weight. Other measurements were made in some, but not all, experiments. These were: e, respiratory exchange by collection of expired air in a Tissot gasometer after the subject was in a steady state, analysis for carbon dioxide and oxygen with the Haldane apparatus, and calculation of the oxygen consumption by standard procedures (Haldane, 1934; Peters and Van Slyke, 1932); f, protein by the micro Kjeldahl method of Ma

Fluid and fuel intake during exercise

“…A person's physiological drive for fluid intake during exercise is perceived through 'thirst mechanisms' and it has long been known that when given ad libitum access to fluid, and thus drink voluntarily, that these mechanisms compel people to drink at a rate that replaces approximately one-half of their fluid losses and at best two-thirds (Pitts and Consolazio, 1944;Hubbard et al, 1984). The concept that thirst during exercise does not drive people to take in fluid at the rate of fluid loss is termed 'voluntary dehydration'.…”

“…Furthermore, the scientific literature in the 1960s was interpreted to suggest that dehydration by less than 3-4% of body weight caused insignificant hyperthermia or impairment of physiological function and performance, although it was recognized that dehydration by more than 4% is dangerous to health (Wyndham and Strydom, 1969). This belief that dehydration by 3-4% was tolerable prevailed despite evidence to the contrary from carefully conducted studies around the time of the Second World War that had clearly shown that dehydration by less than 3-4% during prolonged marching in the heat impaired performance and caused exhaustion and collapse (Pitts and Consolazio, 1944;Adolph, 1947;Ladell, 1955; Coyle and Montain, 1992a,b). The athletic community of this era appears to have remained unaware or unconvinced that the demands of marching were not unlike athletic endurance events, except, of course, for the speed and practical aspects of drinking while running compared with walking.…”

Assessment of Cardiac Cost of Two Age Groups of Brick Carriers During Summer in Different Unorganized Brick making Sector in West Bengal, India

“…So a continuous and speedily performed job can create heavy work load to the carriers and it increases more in summer seasons because of increasing environmental temperature and humidity (Azer and McNall, 1972;Hancock and Vasmatzidis, 2003). The heat exposure caused dehydration in the worker working outside (Pitts et al, 1994;Coyle, 2004). In West Bengal, average environmental temperature during summer seasons ranges between 28°C -44°C, specifically April and May are the hottest months.…”

Summary and Outlook

“…After a long strenuous physical activity, subjects usually stop spontaneous exclusive water intake as soon as the deficit of functional water volume is balanced, that is, long before the initial total body water volume and body weight is regained. The difference between initial and actual body weight is called 'involuntary dehydration' (Pitts et al, 1944). The replenishment of the depleted glycogen bound and sodium fixed water pools presumes additional intake of glucose or gluconeogenic substrates and sodium chloride, for example, by special drinks or a meal (Kampmann et al, 2003).…”