Occupational heat exposure standards define permissible thermal conditions on the basis of metabolic heat production. However, even when energy expenditure is low, upright posture and repetitive upper limb motion may influence thermoregulatory behaviour through increased cardiovascular stress. The present study was undertaken to examine the relationship between work activity, thermal exposure and cardiac strain among women laundry workers engaged in sedentary, repetitive work activity. Ambient temperatures, work activity and heart rate were recorded during complete work shifts for 11 women over three days in summer and three days in winter. Workstation temperatures were significantly higher in summer. Analysis of continuous recordings of heart rate with respect to work activity showed (i) parallel increases in pulse rate and dominant arm movement frequency; (ii) different patterns of heart rate fluctuations for the two work cycles, with peaks during particular sub-tasks and when arms were in elevated positions. Recommended limits for cardiac strain indices were surpassed in both seasons, although in summer they were exceeded significantly more frequently. The part of cardiac effort attributable to thermoregulatory adjustments was also higher in summer while the fraction reflecting metabolic needs did not change with the season. These findings demonstrate high levels of cardiac strain in this work situation and raise the question of redefining heat exposure standards to include the prevention of excessive cardiac strain resulting from cumulative effects of heat load and ergonomic stressors.
Les Québécoises : dix ans plus tard Volume 15, numéro 1, juin 1990 URI : id.erudit.org/iderudit/031549ar
Although there is an abundant literature on the health effects of occupational heat exposure, very few authors have addressed the question of the effects of heat stress on women workers. Knowledge about the effects of work in hot environments is mainly derived from the study of "heavy" muscular activity and current heat exposure standards are based on an energy criterion according to metabolic load. Metabolic load does not reflect cardiac strain associated with sedentary, repetitive work, involving static effort. The research presented here was conducted in an industrial laundry with 11 women mangle operators exposed to moderate heat stress during the summer months and whose work activity is classified as light on the basis of energy expenditure. Physiological and symptomatological responses, work activity and ambient temperature were assessed over 3 complete work days in summer and in winter. Recorded and perceived temperature, discomfort, feelings of fatigue and symptoms of thermal stress were significantly higher in summer than in winter. Symptoms of drowsiness and musculo-skeletal aches were reported equally in both seasons. Heart rate was high in both seasons, as were calculated indices of cardiac strain. Recommended limits for cardiac strain were surpassed significantly more often in summer than in winter. It is suggested that threshold levels should be redefined to include the prevention of cardiac strain resulting from cumulative effects of heat stress and sedentary, repetitive activity, typical of many women's job with low energy requirement.
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