Author(s): HABAY, J., EZZY, Q., ARENALES ARAUZ, Y.L., PATTYN, N., VAN CUTSEM, J., ROELANDS, B. , Institution: VUB, Country: BELGIUM, Abstract-ID: 863

INTRODUCTION:
Both sleep and mental fatigue (MF) influence cognitive and physical performance [1, 2]. However, while they are theorized to share similar effects and mechanisms, not much is known about the link between sleep and MF variables. Moreover, caffeine is said to influence both states, but no research has yet included caffeine use as a confounding variable.
METHODS:
Ninety-nine healthy individuals (54 male, 32.7 ± 8.7 y, 175.1 ± 9.9 cm, 70.0 ± 11.7 kg, 48.4 ± 9.4 ml/min.kg) were included in this randomized crossover trial. Participants visited the lab three times (familiarization, intervention (INT) and control (CON)) and were required to either perform a 45 min Stroop task (INT) or watch a documentary (CON). The level of MF was quantified using a visual analogue scale (MVAS). A GoNoGo task (cognitive performance) and cycling time trial (physical performance) were used to quantify the behavioral effects of MF. Sleep variables included quality, quantity, chronotype and sleepiness. Caffeine use was measured using the revised caffeine consumption questionnaire. A one way ANCOVA and regression analyses were used to explore the links between all variables.
RESULTS:
There was a significant rise in MF as evidenced by MVAS values (MF = 69.0 ± 18.5 AU; CON = 26.4 ± 17.6 AU; p<0.001; d = 1.9). MF negatively impacted Go reaction time (MF = 382.4 ± 33.3 ms; CON = 369.5 ± 32.2 ms; p <0.001; d = 0.6), Go accuracy (MF = 98.1 ± 1.6%; CON = 98.7 ± 1.2%; p<0.001; d = 0.4), and NoGo accuracy (MF = 88.1 ± 9.8 %; CON = 91.2 ± 7.4%; p < 0.001; d = 0.4). Distance in the time trial showed a trend to significance (MF = 12.6 ± 1.8 km; CON = 12.7 ± 1.7 km; p = 0.078; ES = 0.2). The one way ANCOVA showed no influence of chronotype on MF variables. Moreover, only two regression models showed a significant link between MF and sleep, with an increase in MVAS leading to an increase in sleepiness (p = 0.040; Adj. R2 = 0.03), and a decrease in sleep quality leading to a worsening of reaction time (p = 0.035; Adj. R2 = 0.04). Two variables (sleep quantity (p = 0.099; Adj. R2 = 0.02) and sleepiness (p = 0.120; Adj. R2 = 0.02)) showed a trend to significance, with an worsening of both leading to a higher effect of MF on time trial distance. Caffeine usage had no influence on the performed analyses.
CONCLUSION:
The results of the present study show almost no relationship between sleep, MF and caffeine variables. Possible explanations for the lack of relationship are specific differences in physiological mechanisms and the limited variability of sleep data. Therefore, future research is necessary to gain further insights into sleep, MF and their internal connections.

1. Habay J, et al. Interindividual Variability in Mental Fatigue-Related Impairments in Endurance Performance: A Systematic Review and Multiple Meta-regression. Sports Medicine - Open. 2023;9(1).
2. Craven J, et al. Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review. Sports Medicine. 2022;52(11):2669-90.