Simultaneous assessment of motor and cognitive tasks reveals reductions in working memory performance following exercise in the heat

Abstract

This study tested the hypothesis that, following exercise in the heat, motor task performance will be impaired when assessed simultaneously with a cognitive task. In a randomized, crossover and counterbalanced design, twelve healthy adults (23 ± 2 years, 5 women) completed four 10-minute exercise circuits involving upper and lower body exercise in a moderate (18.1 ± 1.7°C, 38 ± 10% relative humidity) and a hot (40.3 ± 1.1°C, 26 ± 5% relative humidity) environment. Experimental testing was completed in a temperate thermal environment before exercise (~25°C) and in either the moderate or hot environment following exercise. The 3 Back test (a test of working memory) was used as the cognitive task and postural sway was used as the motor task. Cognitive and motor task performance assessments were conducted both individually (solo) and simultaneously (dual). At the end of exercise, core temperature (by 0.4 ± 0.3°C, P < 0.001), heart rate (by 12 ± 18 bpm, P = 0.025), and mean skin temperature (by 7.6 ± 0.8°C, P < 0.001) were higher in the Hot trial compared to Moderate. During solo testing, postural sway increased from pre- to post-exercise in the Hot (P ≤ 0.028), but not the Moderate (P ≥ 0.261) trial. During dual testing, postural sway did not differ between trials (P ≥ 0.065) or over time (P ≥ 0.094). During solo testing, 3 Back performance did not differ between trials (P = 0.810) or over time (P = 0.707), but during dual testing 3 Back performance following exercise was reduced in the Hot compared to the Moderate trial (P = 0.028). Simultaneous assessment of motor and cognitive tasks reveals that motor performance is reduced following exercise in the heat. .

Keywords: Cognitive function; exercise; heat stress; hyperthermia; postural sway.

Figure 1.

Core temperature (A & B), heart rate (C & D), and mean skin temperature (E & F) measured immediately before completing the postural sway, 3 Back, and dual task tests before (on left) and after (on right) exercise that was completed in a moderate and hot thermal environment. Data are presented as mean with individual values. Data were analyzed using linear mixed models and P-values for the linear mixed model are presented.

Figure 2.

Core temperature (a), heart rate (b), and mean skin temperature (c) measured immediately before (Baseline) and at the end of each exercise circuit completed during exposure to a moderate and hot thermal environment. Data are presented as mean ± SD. Data were analyzed using linear mixed models and P-values for the linear mixed model are presented. If a significant main effect or interaction was identified, Sidak’s multiple comparisons test was utilized. * Indicates different from Moderate trial at same timepoint (P ≤ 0.025).

Figure 3.

Solo (on left) and dual (on right) task measures of postural sway area (A & B) and length (C & D) measured immediately before (Pre-Exercise) and after (Post-Exercise) exercise that was competed in a moderate and hot thermal environment. Data are presented as mean with individual values. Data were analyzed using linear mixed models and P-values for the linear mixed model are presented. If a significant main effect or interaction was identified, Sidak’s multiple comparisons test was utilized, with P-values for the pairwise comparisons between Pre-Exercise and Post-Exercise and associated effect sizes (Cohen’s d_z) presented.

Figure 4.

Solo (on left) and dual (on right) task measures of 3 Back performance (percent correct answers, A & B) and response latency (C & D) measured immediately before (Pre-Exercise) and after (Post-Exercise) exercise that was competed in a moderate and hot thermal environment. Data are presented as mean with individual values. Data were analyzed using linear mixed models and P-values for the linear mixed model are presented. If a significant main effect or interaction was identified, Sidak’s multiple comparisons test was utilized, with P-values for the pairwise comparisons between Pre-Exercise and Post-Exercise and associated effect sizes (Cohen’s d_z) presented. * Indicates different from Moderate trial at same Post-Exercise timepoint (P = 0.028, d_z = 0.844).