A meta-analysis of performance response under thermal stressors.

OBJECTIVE: Quantify the effect of thermal stressors on human performance.
BACKGROUND: Most reviews of the effect of environmental stressors on human performance are qualitative. A quantitative review provides a stronger aid in advancing theory and practice.
METHOD: Meta-analytic methods were applied to the available literature on thermal stressors and performance. A total of 291 references were collected. Forty-nine publications met the selection criteria, providing 528 effect sizes for analysis.
RESULTS: Analyses confirmed a substantial negative effect on performance associated with thermal stressors. The overall effect size for heat was comparable to that for cold. Cognitive performance was least affected by thermal stressors, whereas both psychomotor and perceptual task performance were degraded to a greater degree. Other variables were identified that moderated thermal effects.
CONCLUSION: Results confirmed the importance of task type, exposure duration, and stressor intensity as key variables impacting how thermal conditions affect performance. Results were consistent with the theory that stress forces the individual to allocate attentional resources to appraise and cope with the threat, which reduces the capacity to process task-relevant information. This represents a maladaptive extension of the narrowing strategy, which acts to maintain stable levels of response when stress is first encountered. APPLICATION: These quantitative estimates can be used to design thermal tolerance limits for different task types. Although results indicate the necessity for further research on a variety of potentially influential factors such as acclimatization, the current summary provides effect size estimates that should be useful in respect to protecting individuals exposed to adverse thermal conditions.