The Individual Response To Mental Fatigue: Preliminary Analysis Of The Role Of Age And Sex

Mental fatigue is a prominent problem in today’s world, negatively influencing both cognitive as well as physical performance. Recent evidence points toward a large range of interindividual differences in these effects, and a contribution of individual features that determine these differences. However, these features have not been extensively investigated in relationship with one another. PURPOSE: To investigate the role of age and sex and their interaction in the effect of mental fatigue on physical performance. METHODS: The results are part of an ongoing randomized crossover trial. Participants were required to visit the laboratory on three different occasions (familiarization, intervention and control). Mental fatigue was induced using a 45 min Stroop task, while the control condition consisted of watching an emotionally neutral documentary. The level of mental fatigue was assessed using subjective manipulation checks. A 15 min time trial assessed physical performance. Influence of age (groups: 18-30y; 31-50y) and sex was investigated using a two way ANOVA on delta performance (distance) values. RESULTS: 36 participants were included in the preliminary analysis (19♂; 17♀; mean age = 28 ± 8 y [min = 20 y, max = 50y]). Subjective measures showed a significant increase in mental fatigue over time during and after the Stroop task (Mean difference = 32.222; p < 0.001; ηp2 = 0.831), and a significantly higher level of fatigue in the intervention compared to the control condition (Mean difference = 24.75 ± 21.82; p < 0.001; d = 1.13). This higher level of mental fatigue did not significantly alter distance (Mean Intervention = 12.02 ± 1.58 km; Mean Control = 12.24 ± 1.40 km; p = 0.201; d = 0.22) during the time trial independent of groups. However, an interaction effect (F = 6.344; p = 0.017; ηp2 = 0.165) was found between sex and age groups for the difference in distance between the intervention and control condition. CONCLUSION: Preliminary results show that age and sex interact to influence the effect of mental fatigue on physical performance. Specifically, men seem to get more susceptible to mental fatigue, while women seem to get more resistant to mental fatigue when they get older. These results have implications for both fundamental as well as applied research, paving the way towards a greater understanding of mental fatigue.