[Physical cost of working under conditions of thermal load].

The objective of this study was to assess the effect of physical load and thermal load on changes in physiological cost of work. A group of 25 students aged 23 +/- 2 years; height 178 +/- 6 cm and weight 72 +/- 11.2 kg, were tested on a bicycle ergometer with physical load of 25, 50, 75, 100 and 150 watts in a climatic chamber at air temperature ta (the mean temperature = 20.5 degrees C) and relative humidity (the mean relative humidity = 68%) and at thermal load WBGT = 27 degrees C. The following parameters were measured: general physical fitness, minute lung ventilation, energy expenditure, relative workload, mechanical efficiency rate, pulse rate and coefficients of correlation between these values. In comparison to values noted under conditions of moderate microclimate, minute lung ventilation, energy expenditure, relative workload and pulse rate were significantly enhanced and coefficient of mechanical lowered at all physical loads under conditions of thermal load WBGT = 27 degrees C. The study revealed significant collaboration between pulse rate at work and increase of minute lung ventilation as well as between energy expenditure at work. There was positive correlation between minute lung ventilation and absolute energy expenditure and %VO2max, and negative correlation between mechanical efficient rate and minute lung ventilation, absolute energy expenditure and %VO2max. The study showed an increased physiological cost of work under conditions of thermal load resulting in declined work efficiency and increased effort necessary to perform individual tasks.