Performance in complex motor tasks deteriorates in hyperthermic humans

Abstract

Heat stress, leading to elevations in whole-body temperature, has a marked impact on both physical performance and cognition in ecological settings. Lab experiments confirm this for physically demanding activities, whereas observations are inconsistent for tasks involving cognitive processing of information or decision-making prior to responding. We hypothesized that divergences could relate to task complexity and developed a protocol consisting of 1) simple motor task [TARGET_pinch], 2) complex motor task [Visuo-motor tracking], 3) simple math task [MATH_type], 4) combined motor-math task [MATH_pinch]. Furthermore, visuo-motor tracking performance was assessed both in a separate- and a multipart protocol (complex motor tasks alternating with the three other tasks). Following familiarization, each of the 10 male subjects completed separate and multipart protocols in randomized order in the heat (40°C) or control condition (20°C) with testing at baseline (seated rest) and similar seated position, following exercise-induced hyperthermia (core temperature ∼ 39.5°C in the heat and 38.2°C in control condition). All task scores were unaffected by control exercise or passive heat exposure, but visuo-motor tracking performance was reduced by 10.7 ± 6.5% following exercise-induced hyperthermia when integrated in the multipart protocol and 4.4 ± 5.7% when tested separately (both P < 0.05). TARGET_pinch precision declined by 2.6 ± 1.3% (P < 0.05), while no significant changes were observed for the math tasks. These results indicate that heat per se has little impact on simple motor or cognitive test performance, but complex motor performance is impaired by hyperthermia and especially so when multiple tasks are combined.

Global REACH 2018: The influence of acute and chronic hypoxia on cerebral haemodynamics and related functional outcomes during cold and heat stress

“…Piil and colleagues recently showed that the negative impact of hyperthermia was exposed only when task complexity was maximised (Piil et al . ). Although the pro/anti‐point task (which combines all of the tasks, i.e.…”

“…; Piil et al . ). The link between CBF and CDO 2 to cognitive functioning is complex in these environments.…”

“…; Piil et al . ). Whole body cooling decreases both central and peripheral nerve conduction velocity and has been shown to slow central information processing (Rammsayer et al .…”

“…The heat-induced reduction in CBF is mediated primarily by arterial hypocapnia secondary to heat-induced hyperventilation; this observation is evidenced by a partial (Brothers et al 2009) or full (Nelson et al 2011;Bain et al 2013) restoration of CBF during heat stress when eucapnia is acutely restored or when hyperventilation is voluntarily supressed (Tsuji et al 2015(Tsuji et al , 2019. Functionally, each of these stressors in isolation -hypoxia, cold, and heat -have been shown to impair cognitive function (Simmons et al 2008;Muller et al 2012;Paulauskas et al 2015;Piil et al 2017). The link between CBF and CDO 2 to cognitive functioning is complex in these environments.…”

“…Some reports show cognitive impairments with acute and prolonged hypoxia despite global CDO 2 and CMRO 2 being maintained, a conundrum that might be partly explained by regional reductions in CBF that become more pronounced with continued hypoxic exposure (Lawley et al 2017). Severe heat stress causes large decreases in CDO 2 but CMRO 2 is maintained or even increased and cognitive impairments are observed only when the task complexity is maximised (Nybo et al 2002b;Trangmar et al 2015;Piil et al 2017). Whole body cooling decreases both central and peripheral nerve conduction velocity and has been shown to slow central information processing (Rammsayer et al 1995).…”