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In order to evaluate the benefit to be derived from the use of the E47 field protective mask drinking device, endurance in exhausting work in grade walking in a warm environment (46 C dry bulb, 23 C wet bulb) was measured before and after 6 hr of sweating. In nine men, the average dehydration was 4.3% of the body weight on the first day with restricted water intake, and 1.9% on a second day with unrestricted water intake by means of the drinking device. Endurance was reduced by 48% on the first day and by 22% on the second day. One canteen full of water would provide only a marginal benefit. Under these conditions, an intake of four canteens would be required to maintain optimal endurance. Exposure to heat and dehydration was accompanied by a hyperventilation that in four of the men exceeded 21 1/min. (Author)

For two men walking on a treadmill and wearing two layers of permeable clothing, the same physiological strain measured by the rate of increase in mean body temperature could be produced a) next to a building outdoors in the sunshine with an average air temperature of 85 F and humidity of 20 mm Hg and b) indoors with the same humidity and an air temperature 10 F higher. Under these conditions, the underwear was mainly wet with sweat and the outer layer was mainly dry. In comparable indoor tests on a third subject, the temperature of the underwear approached equilibrium 1 or 2 F lower than the temperature of the skin at air temperatures of 85 and 115 F. The error in calculating clothing insulation introduced by assuming the clothing to be dry is determined by the size and direction of the temperature gradient between skin and air. Adding 10 F to the indoor air temperature does not duplicate all the effects of sunshine. Submitted on September 15, 1961

The objectives of the investigation were to find the intensities of work at which the reduction in endurance associated with inspiratory resistance would be the greatest and to test various hypotheses to account for the reduction. The following conclusions were reached: The reduction in endurance in exhausting work caused by an added inspiratory resistance is greater when the intensity is such that exhaustion is reached in from 5 to 15 minutes than when higher intensities of work lead to exhaustion in a shorter time; of the various factors examined in this report, the sense of impending exhaustion appears to be associated most closely with the reduction of the duration of expiration to a minimum value characteristic of the individual; in exhausting work, men can withstand the large elevation in alveolar carbon dioxide associated with the inhalation of carbon dioxide mixture better than the smaller but still substantial elevation in alveolar carbon dioxide associated with an added inspiratory resistance. (Author)

In initial 20-sec periods of running on the treadmill, raising the slope to 12% increased by 50% the integrated muscle action potential, recorded from the under side of the thigh, without affecting the ventilation in four men. Five men worked for 1 min at four tasks, two on the treadmill and two on the horizontal cycle ergometer. Each pair of tasks consisted of slow and rapid leg movement at the same rate of work. Ventilation often continued at about the resting rate for the first few seconds of work, unaffected in any significant way by frequency of leg movement. In the subject responding to the onset of exercise by a sudden sharp involuntary increase in ventilation, the nature of the nervous respiratory drive is not clear. Whatever drive arises from the work itself may be strongly modified by training or by complexities in the work situation. leg movement; muscle action potential; nervous respiratory drive Submitted on May 16, 1963

The duration of maximum voluntary apnea (B) with fully inflated lungs in one experienced subject was determined during and immediately after treadmill exercise, with oxygen uptake (M) ranging up to...

The influence of intravenously injected atropine sulfate on sweating was measured in three men by continuous recording of body weight. Most of the skin surface was kept dry by air movement at 1.5 m/sec. The sequence of events was: completion of injection in 1.1 min; cardiac acceleration in 1.3 min; and inhibition of sweating in 3.5 min. The minimum rate of weight loss occurred at a dose of 0.5 mg; larger doses prolonged the inhibition without intensifying it. Heat storage was equal to an average of 92% of the deficit in evaporative heat loss. Although sweating returned to the initial rate within an hour, the normal increase in sweating at elevated body temperatures was prevented for the next hour. Sweating responds to atropine almost as rapidly as the cardiac rate. The degree of inhibition is independent of the initial rate of sweating. heart rate; skin temperature; rectal temperature; heat exposure; heat loss by evaporation; man continuous recording of body weight; exercise Submitted on June 24, 1964

Before the injection of atropine, sweating in resting men, measured by continual weighing, increased with environmental temperature from 2 gm/min at 35C to 13 gm/min at 52C. Atropine sulfate was infused intravenously at rates between 0.01 and 0.10 mg/min after rapid intravenous injections of from 0 to 0.5 mg. Larger rates of infusion were required to inhibit sweating at 52 than at 35C. The accumulated dose (y), in micrograms per kilogram required to inhibit sweating by one-half, increased with the control rate of sweating (x) in grams per square meter minute according to the equation y = (2.6 plus or minus 0.3) + 0.76 plus or minus 0.15) x. The rapid recovery after the end of the infusion and the failure of the inhibition to progress as the dose accumulated at slow infusion rates suggested that the effect of atropine was being opposed by an added stimulus generated by the increase in skin temperature during the period of reduced sweating. The theory of a surmountable antagonism between atropine and endogenous acetylcholine at receptor sites on the sweat gland appears to explain the results. (Author)

Two men ran for 20 or 60 seconds while inhaling air, oxygen or 4% carbon dioxide. Inspired respiratory minute volume was determined for each breath. Ventilation increased suddenly in the first breath with minimal changes in end-expiratory carbon dioxide tension and respiratory exchange ratio to a rate that remained constant for 20 seconds before increasing further. The rate of carbon dioxide output was uniform during the first 20 seconds. A 12% grade did not increase ventilation or oxygen uptake during runs of 20 seconds, but in the first minute of recovery, ventilation was 64% greater than after level runs. Inhalation of oxygen inhibited ventilation by 24% in the 20-second periods before and after the end of a 60-second run. Inhalation of carbon dioxide begun at rest produced increments in ventilation and end-expiratory carbon dioxide tension that varied little during running and recovery. In the 20-second runs ventilation varied with speed but appeared independent of ultimate metabolic cost. Submitted on January 21, 1960

Men worked themselves to exhaustion on a treadmill at 3.5 mph and a grade beginning at 10 percent and increasing by one percent per minute in a room at 46 degrees C. The men were first overheated by enclosure in a plastic bag or by immersion in a warm bath. Enough water was drunk to prevent dehydration. Effects of dehydration on endurance in exhausting work at 46 degrees C, reported previously, appear to be due mainly to overheating during the period of water restriction.

At 18 C the heart began to beat faster at the beginning of treadmill exercise. In the first 10 beats, the average increase above the previous standing rate amounted to 12 beats/min in walking and 28 beats/min in running. At 38 C or when atropine was injected, the standing rate before exercise was rapid; in the immediate response to exercise, the rate increased less than at 18 C without atropine, remained the same as in standing, or decreased temporarily below the standing rate by as much as 40 beats/min. These early responses were attributed to changes in vagal inhibition. After the start of the run there was a secondary increase between the 25th and 60th sec that averaged 22 beats/min at the peak of the response to atropine. This secondary increase was attributed to accelerator activity. Submitted on August 27, 1962

Three groups of men wearing the CBR protective uniform were exposed to six conditions of varying heat, humidity, wind, exercise, and initial water content of the clothing. Each condition was repeated with and without a 2-mg dose of atropine sulfate. In troops wearing the CBR protective uniform who inject a 2-mg dose of atropine into themselves on the mistaken assumption of an exposure to an anticholinesterase agent, the rise in rectal temperature caused by the inhibition of sweating by atropine can be kept within safe limits if exercise is avoided and the clothing is wet with sweat at the time of injection.

Breath holding time was measured after exercise at five grades of work in a group of 12 men. An average of 1.4 seconds elapsed between the signal, which was given without warning, and the cessation...

The performance of one man in maximal work has been evaluated over a period of 28 years. The highest attainable heart rate declined from 172 to 160 and oxygen consumption from 3.3 to 2.8 liters per...