Abstract
This study investigated the effects of heat exposure on physical and cognitive performance during an intermittent exercise protocol so as to reflect the incremental fatigue experienced during team sports. Twelve well-trained male team sport players completed an 80-minute cycling intermittent sprint protocol (CISP), alongside computerized vigilance and congruent (i.e., simple) and incongruent (i.e., complex) Stroop tasks of cognitive functioning, in two counterbalanced temperature conditions; hot (32°C[50%rh]) and control (18°C[50%rh]). Incongruent Stroop accuracy declined over time (p = .002), specifically in the second (Mdiff = –3.75, SD = 0.90%, p = .009) and third (Mdiff = –4.58, SD = 1.22%, p = .019) quarters compared to the first quarter of the CISP; but there were no differences between temperature conditions. Congruent Stroop reaction time (RT) was quicker in the second quarter of exercise in the hot condition (M = 561.99, SD = 112.93 ms) compared to the control condition (M=617.80, SD = 139.71 ms; p = .022), but no differences were found for congruent Stroop accuracy nor vigilance measures. Additionally, peak power output was lower during the third quarter of the CISP in the hot condition (M = 861.31, SD = 105.20 W) compared to the control condition (M = 900.68, SD = 114.84 W; p < .001). Plasma normetanephrine and metanephrine concentrations increased from pre- to post-CISP (Mdiff = +616.90, SD = 306.99, p < .001; and Mdiff = +151.23, SD = 130.32, p = .002, respectively), with a marginal interaction suggesting a higher normetanephrine increase from pre- to post-CISP in the hot versus the control condition (p = .070). Our findings suggest that accuracy for more complex decisions suffered during prolonged high-intensity intermittent exercise, perhaps due to exercise-induced catecholamine increases. Athletes may have also reduced physical effort under increased heat exposure, indicating how cognitive performance may be sustained in physically demanding environments.
Highlights
In team sports such as soccer, elite-level players often cover distances of 10 km in a single match, running at average intensities that are close to their anaerobic threshold, with numerous intermittent explosive bursts of activity (Stølen et al, 2005)
Bonferroni pairwise comparisons for the interaction revealed that, no differences in core temperature were found in the first quarter of the Cycling Intermittent Sprint Protocol (CISP) (p 1⁄4 .107, d 1⁄4 0.42), core temperature was significantly higher in the hot (M 1⁄4 38.40C, standard deviations (SD) 1⁄4 0.43) compared to the control condition (M 1⁄4 37.92C, SD 1⁄4 0.53) (p 1⁄4 .015, d 1⁄4 0.99) during the second quarter
Marginal differences were observed in the third quarter of the CISP, whereby core temperature was higher in the hot (M 1⁄4 37.87C, SD 1⁄4 0.32) compared to the control condition (M 1⁄4 37.56C, SD 1⁄4 0.45) (p 1⁄4 .076, d 1⁄4 0.79)
Summary
In team sports such as soccer, elite-level players often cover distances of 10 km in a single match, running at average intensities that are close to their anaerobic threshold, with numerous intermittent explosive bursts of activity (e.g. sprinting, jumping) (Stølen et al, 2005). Prior to receiving the ball, a soccer player must show spatial awareness of vacant space and/or player positions before deciding where or when to play the ball. In such situations, players simultaneously apply vigilance, selective attention and workingmemory of player positions under both time restrictions and physical exertion (Heppe et al, 2016). Research has revealed that most goals in soccer are conceded in the last 15-minutes of matches, suggesting that physical fatigue typically experienced in the latter stages of match-play may increase the likelihood of mistakes in cognitive skills (Alberti et al, 2013). Progressive fatigue observed from prolonged exercise, such as during team sport performance, has been attributed to diminished muscle glycogen stores, hyperthermia, increased loss of body fluids, and altered synthesis and metabolism of neurotransmitters (Meeusen et al, 2006; Mohr et al, 2012)
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