Nutritional status and physical work capacity

The functional consequences of nutritional intake and resulting nutritional status are reviewed in terms of maximal oxygen consumption, physical work capacity, heart rate response to exercise, work productivity, and endurance at submaximal work loads. The results of both acute “laboratory” and chronic “naturally occurring” malnutrition are considered as well as the effects of dietary supplementation and recovery from previously existing undernutrition. Obesity and anemia are also treated as separate but related nutritional entities.     

Effect of primary hypohydration on physical work capacity

Physical work capacity (PWC₁₈₀) was assessed with different levels of hypohydration in 25 heat-acclimatized male volunteers in hot dry (45°C DB, 30% RH) and hot humid (39°C DB, 60% RH) conditions equated to a heat stress level of 34°C on the WBGT scale. Heat acclimatization was carried out by exposing the subjects for 8 consecutive days in a climatic chamber with moderate work for two 50 min work cycles and 10 min intervening rest pauses. Acclimatization resulted in significant decreases in heart rate (27 bpm), oral temperature (0.8°C), mean skin temperature (1.2°C) and a significant increase in sweating rate (120 g h^–1 m^–2). Day-to-day variations in body hypohydration levels during heat acclimatization were not significantly different, although water intake was found to increase significantly from day 3 onwards when the subjects were in ad lib water intake state. The heat acclimatized subjects were then hypohydrated to varying degrees, viz. 1%, 2% and 3% body weight deficit, with moderate work in heat in the climatic chamber and after successful recovery from the effects of thermal stress and exercise; their physical work capacity was assessed individually. Physical work capacity was found to decrease significantly with hypohydration as compared to controls. The decrease was of the order of 9%, 11% and 22% in the hot dry condition and 6%, 8% and 20% in the hot humid condition with hypohydration levels of 1%, 2% and 3% respectively. The decrease was more pronounced during 3% hypohydration level under both heat stress conditions. This decrease was in spite of significant increases in maximal ventilation. However, the PWC₁₈₀ under the two heat stress conditions, when compared, did not reveal any significant difference. It was concluded that the heat stress vehicle did not adversely affect the physical work capacity. On the other hand, the decreases in physical work capacity were found to be closely related to the primary hypohydration level in heat-acclimatized tropical subjects.Abbreviations WBGT wet bulb globe temperature - bam beats per minute - YSI Yellow Springs Instrument - EKG electrocardiogram     

The physical work capacity of the body in experiments with the combined action of hypokinesia and radiation]

After combined exposures to hypokinesia and radiation, hybrid CBA x C57BL mice of the first generation showed a drop in their working capacity as estimated by the rate of swimming through a limited distance. It was found that hypokinesia was a sufficiently strong stressor, no less affecting the working capacity than ionizing radiation in LD50. There was no summation in effects of these irritants with respect to the drop in working capacity.     

Seasonal and individual characteristics of the response of the fibrinolytic system of blood to physical exercise

The response of the fibrinolytic system of the blood of 33 untrained subjects (16 males and 17 females 18 years old) to a single 20-min bicycle-ergometric large-capacity load (N _male = 2.66 W/kg, N _female = 2.3 W/kg) was studied for 1 year. It is known that the blood fibrinolytic activity at rest has seasonal characteristics: it is relatively high in autumn and spring and low in winter and summer. On average, physical activity in winter and summer stimulates the blood clot lysis, whereas in autumn and spring this stimulation is not observed. The direction and intensity of the response of the fibrinolytic system to exercise have individual features: in autumn and spring they depend on its initial state (increase when the blood FA is low and decrease when it is high) and fluctuate widely, whereas in winter and summer this dependence is not observed. According to the direction of response to the load and its persistence, three types of responses can be distinguished: (a) hyperfibrinolytic, which is characterized by an increase in FA during exercise throughout the year, with a constantly low initial level of fibrinolytic activity at rest; (b) hypofibrinolytic, which is characterized by a stable suppression of fibrinolysis after exercise regardless of the season and the initial level of fibrinolytic activity, with a high fibrinolytic activity at rest in autumn and spring and a low fibrinolytic activity in winter and summer; and (c) unstable, in which the direction of the response of the fibrinolytic system to exercise varies. It is concluded that the development of thromboembolic complications after exercise can be expected with the highest and lowest probability in the subjects with the hypofibrinolytic and hyperfibrinolytic response, respectively.