Abstract
PurposeTo evaluate the prevalence of dehydration in occupational settings and contextualize findings to effects on performance in cognitively dominated tasks, simple and complex motor tasks during moderate and high heat stress.MethodsThe study included an occupational part with hydration assessed in five industries across Europe with urine samples collected from 139 workers and analyzed for urine specific gravity. In addition, laboratory experiments included eight male participants completing mild-intensity exercise once with full fluid replacement to maintain euhydration, and once with restricted water intake until the dehydration level corresponded to 2% bodyweight deficit. Following familiarization, euhydration and dehydration sessions were completed on separate days in random order (cross-over design) with assessment of simple motor (target pinch), complex motor (visuo-motor tracking), cognitive (math addition) and combined motor-cognitive (math and pinch) performance at baseline, at 1°C (MOD) and 2°C (HYPER) delta increase in body core temperature.ResultsThe field studies revealed that 70% of all workers had urine specific gravity values ≥1.020 corresponding to the urine specific gravity (1.020±0.001) at the end of the laboratory dehydration session. At this hydration level, HYPER was associated with reductions in simple motor task performance by 4±1%, math task by 4±1%, math and pinch by 9±3% and visuo-motor tracking by 16±4% (all P<0.05 compared to baseline), whereas no significant changes were observed when the heat stress was MOD (P>0.05). In the euhydration session, HYPER reduced complex (tracking) motor performance by 10±3% and simple pinch by 3±1% (both P<0.05, compared to baseline), while performance in the two cognitively dominated tasks were unaffected when dehydration was prevented (P>0.05).ConclusionDehydration at levels commonly observed across a range of occupational settings with environmental heat stress aggravates the impact of hyperthermia on performance in tasks relying on combinations of cognitive function and motor response accuracy.
Highlights
The importance of preventing dehydration has received much attention in health and worksafety advisories, from sport coaches, highlighted during hot periods in medias, emphasized in commercial campaigns and recognized by the physiological society as a very important strategy for minimizing the detrimental effects of heat stress on physical performance [1,2]
The field studies revealed that 70% of all workers had urine specific gravity values !1.020 corresponding to the urine specific gravity (1.020±0.001) at the end of the laboratory dehydration session
HYPER was associated with reductions in simple motor task performance by 4±1%, math task by 4±1%, math and pinch by 9±3% and visuomotor tracking by 16±4%, whereas no significant changes were observed when the heat stress was moderate elevation of core temperature (MOD) (P>0.05)
Summary
The importance of preventing dehydration has received much attention in health and worksafety advisories, from sport coaches, highlighted during hot periods in medias, emphasized in commercial campaigns and recognized by the physiological society as a very important strategy for minimizing the detrimental effects of heat stress on physical performance [1,2]. Dehydration accelerates the decline in cerebral blood flow during exercise in heat stress conditions, but the cerebral metabolic rate for oxygen does not decline [19,23,24]. It remains unclear how cognitive functions are affected as long as severe dehydration is prevented i.e. if cognitive functions can be maintained when hydration levels are in the range, which is relevant for working or recreationally active people
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