The Effects Of Daily Mental Fatigue On Exercise Performance In College Age Adults

Artificially induced mental fatigue reduces performance during aerobic exercise tasks, but less is known about how mental fatigue affects strength, power, and reaction time. Artificially induced mental fatigue is useful in quantifying fatigue; however, often exceeds that which naturally occurs throughout the day. PURPOSE: To determine the effects of naturally occurring mental fatigue experienced throughout the day on exercise performance in the morning compared to the evening for college age adults. METHODS: Ten healthy adults (4 male, 6 female; age: 21 + 2 yrs; ht: 172.71 + 9.14 cm; wt: 71.33 + 9.95 kg) completed baseline mental fatigue tests for four days over two weeks. Heart rate variability (HRV), Stroop Effect, and perceived measures of stress (PSS) and mental demand (NASA-TLX) were tested at the same time in the morning (AM) and evening (PM) to quantify normal daily mental fatigue. Participants completed two exercise testing days with one AM and one PM condition. Exercise testing consisted of maximal handgrip strength, maximal vertical jump, reaction time, and a 1500 m rowing test. RESULTS: Participants experienced significant increases in perceived mental demand (t(9) = -6.79; p < .001; g = 2.86), effort (t(9) = -7.33; p < .001; g = 2.29), and frustration (t(9) = -2.55; p = 0.03; g = 3.39) from AM to PM during baseline testing. No differences were found in handgrip (t(9 ) = 0.30; p = 0.77; g = 4.41), vertical jump (t(9) = 0.75; p = 0.47; g = 3.38), reaction time (t(9) = 0.10; p = 0.92; g = 0.16), 1500 m row time to completion (t(9) = -0.733; p = 0.48; g = 21.17), or total watts produced (t(9) = 0.61; p = 0.56; g = 133.72) between the AM and PM conditions. Perceived mental demand (t(9) = -11.26; p < .001, g = 2.23) and effort used to accomplish level of performance throughout the day (t(9) = -4.10; p = .003; g = 4.10) were significantly greater in the PM condition than the AM condition. Perceived stress (t(9) = -0.18; p = 0.86; g = 3.58), HRV (t(9) = -0.39; p = 0.70; g = 37.45), and the Stroop Effect (t(9) = -0.73; p = 0.48; g = 78.12) were not significantly different between the AM and PM conditions. CONCLUSIONS: Participants experienced mental fatigue throughout the day, but with little effect on performance. Mental fatigue may not impact strength, power, or reaction time due to the lack of self-regulation and decision making required for the exercise tasks.