Abstract:Background: Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Mental fatigue has recently been suggested to affect physical performance. Objective: To evaluate the literature on the impairment in physical performance due to mental fatigue and to create an overview of the potential factors underlying this effect. Data Sources: Two electronic databases, PubMed and Web of Science (until 28 April 2016) were searched. Eligibility criteria for selecting studies: Studies had to be designed to test whether mental fatigue influenced performance on a physical task or influenced physiological and/or perceptual responses during the physical task. Studies using short (<30 min) self-regulatory depletion tasks were excluded from the review. Results: Eleven articles were included, of which six were of strong and five of moderate quality. The general finding was a decline in endurance performance (decreased timeto-exhaustion and self-selected power output/velocity or increased completion-time) due to mental fatigue, associated with a higher than normal perceived exertion. Physiological variables traditionally associated with endurance performance (heart rate, blood lactate, oxygen uptake, cardiac output, VO2) were unaffected by mental fatigue. Maximal strength, power and anaerobic work were observed not to be affected by mental fatigue. Conclusion: Duration and intensity of the physical task appear to be important factors in the decrease in physical performance due to mental fatigue. The most important factor responsible for the negative impact of mental fatigue on endurance performance is a higher perceived exertion. Powered by Edit orial Manager® and ProduXion Manager® from Aries Syst em s Corporat ionA E Dear editor, we thank you for the revisions. We also revised the paper once more on grammar and vocabulary and subsequently adjusted some words, rephrased a couple of sentences and removed some redundant sentences (mainly in section 4.5 and 5). We hope you agree with these specific changes and want to emphasize that no changes were made to the content of the manuscript (in order to demonstrate this all deleted words and sentences are also indicated in the manuscript with tracked changes).1. Section 3.4 please number the subsections in this section 3.4. This was adjusted.3. Section 4.5, sentence 1This was adjusted. Compliance with Ethical Standards section S B SM This was adjusted. Conflicts of Interest section S B S MThis was adjusted.6. References list the References list no longer has the corrected formatting that was evident in the Revision 1 version of this list. Therefore, can you please reinstate the Revision 1 version, which incorporated the requested formatting changes from the submitted version. However, please also note that the revised version of the References list in Revision 1 had 77 references, whereas the version in Revision 2 has 82 references. Therefore, the format-corrected version in Revision 1 cannot simply be transplanted into Revision 3 it ...

Fatigue of voluntary muscular effort is a complex phenomenon. To date, relatively little attention has been placed on the role of the central nervous system (CNS) in fatigue during exercise despite the fact that the unwillingness to generate and maintain adequate CNS drive to the working muscle is the most likely explanation of fatigue for most people during normal activities. Several biological mechanisms have been proposed to explain CNS fatigue. Hypotheses have been developed for several neurotransmitters including serotonin (5-HT; 5-hydroxytryptamine), dopamine, and acetylcholine. The most prominent one involves an increase in 5-HT activity in various brain regions. Good evidence suggests that increases and decreases in brain 5-HT activity during prolonged exercise hasten and delay fatigue, respectively, and nutritional manipulations designed to attenuate brain 5-HT synthesis during prolonged exercise improve endurance performance. Other neuromodulators that may influence fatigue during exercise include cytokines and ammonia. Increases in several cytokines have been associated with reduced exercise tolerance associated with acute viral or bacterial infection. Accumulation of ammonia in the blood and brain during exercise could also negatively effect the CNS function and fatigue. Clearly fatigue during prolonged exercise is influenced by multiple CNS and peripheral factors. Further elucidation of how CNS influences affect fatigue is relevant for achieving optimal muscular performance in athletics as well as everyday life.

Brain serotonin (5-hydroxytryptamine, 5-HT) has been suggested to be involved in central fatigue during prolonged exercise. Changes in the ratio of plasma free tryptophan (free Trp) to branched-chain amino acids (BCAA) are associated with altered brain 5-HT synthesis. The purposes of this study were to describe systematically the effects of prolonged exercise on changes in plasma free Trp and BCAA and to examine the effects of carbohydrate (CHO) feedings on these same variables. Eight well-trained men [VO2max = 57.8 (SE 4.1) ml kg-1 min-1] cycled for up to 255 min at a power output corresponding to VO2 at lactate threshold (approximately 68% VO2max) on three occasions separated by at least 1 week. Subjects drank 5 ml kg-1 body wt-1 of either a water placebo, or a liquid beverage containing a moderate (6% CHO) or high (12% CHO) concentration of carbohydrate beginning at min 14 of exercise and every 30 min thereafter. Exercise time to fatigue was shorter in subjects receiving placebo [190 (SE 4) min] as compared to 6% CHO [235 (SE 10) min] and 12% CHO [234 (SE 9) min] (P < 0.05). Glucose and insulin decreased in the placebo group, and free Trp, free-Trp/BCAA, and free fatty acids increased approximately five- to sevenfold (P < 0.05). These changes were attenuated in a dose-related manner by the carbohydrate drinks.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological manipulation of brain serotonergic [5-hydroxytryptamine (5-HT)] activity affects run time to exhaustion in the rat. These effects may be mediated by neurochemical, hormonal, or substrate mechanisms. Groups of rats were decapitated during rest, after 1 h of treadmill running (20 m/min, 5% grade), and at exhaustion. Immediately before exercise rats were injected intraperitoneally with 1 mg/kg of quipazine dimaleate (QD; a 5-HT agonist), 1.5 mg/kg of LY 53857 (LY; a 5-HT antagonist), or the vehicle (V; 0.9% saline). LY increased and QD decreased time to exhaustion (approximately 28 and 32%, respectively; P < 0.05). At fatigue, QD animals had greater plasma glucose, liver glycogen, and muscle glycogen concentrations but lower plasma free fatty acid concentration than did V and LY animals (P < 0.05). In general, plasma corticosterone and catecholamine levels during exercise in QD and LY rats were similar to those in V rats. Brain 5-HT and 5-hydroxyindole-3-acetic acid concentrations were higher at 1 h of exercise than at rest (P < 0.05), and the latter increased even further at fatigue in the midbrain and striatum (P < 0.05). Brain dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were higher at 1 h of exercise (P < 0.05) but were similar to resting levels at fatigue. QD appeared to block the increase in DA and DOPAC at 1 h of exercise, and LY prevented the decrease in DA and DOPAC at fatigue (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The implementation of active workstations might contribute to improving people's health and physical activity levels. The effect of the use of these active workstations on cognition and applied work tasks, such as computer task performance, needs further investigation before conclusions can be drawn. Another aspect that needs further investigation is the implementation of the different active workstations in all age groups.

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To assess the effect of branched-chain amino acids (BCAA) supplementation on endurance performance in the heat, six women and seven men participated in two trials of rest in the heat (Ta = 34.4 +/- 1.8 degrees C; rh = 39 +/- 14%), followed by 40% VO2peak exercise to exhaustion. Subjects ingested 5 mL x kg(-1) of a placebo (PLAC) or BCAA drink every 30 min. Cycle time to exhaustion increased during BCAA (153.1 +/- 13.3 vs 137.0 +/- 12.2 min, P < 0.05) for men and women. Plasma glucose was maintained at baseline values for both drinks; however, women had significantly higher concentrations (5.9 +/- 0.6 vs 4.0 +/- 0.2 mM, P < 0.05). Plasma free fatty acids and ammonia were not influenced by drink or gender but increased over time. BCAA resulted in a significant (P < 0.05) increase in plasma BCAA (1209 +/- 119 vs 496 +/- 44 microM), while F-TRP (9.6 +/- 0.9 vs 12.0 +/- 1.3 microM) and F-TRP:BCAA were decreased (0.009 +/- 0.001 vs 0.024 +/- 0.003 ND) in both men and women. Cardiovascular and thermoregulatory data were similar between treatments for all subjects. Psychological data were not influenced by BCAA. These results indicate BCAA supplementation prolongs moderate exercise performance in the heat.

Many athletes avoid using mouthguards because they believe that they impair their ability to breath and negatively affect performance. Recently, some manufacturers have developed "vented" mouthguards (VentMGs) to address this concern. The purposes of this investigation were to describe the impact of a commercially available "vented" boil-and-bite mouthguard on the physiological responses to graded exercise and to determine whether the use of the same mouthguard influences performance during traditional physical agility tests. Recreationally trained males (n = 15) (age = 24 ± 1 year; (Equation is included in full-text article.)= 43.5 ± 1.9 ml·kg·min; body mass index = 25.2 ± 0.9) completed 3 randomly assigned trials where they wore no mouthguard (control), a traditional mouthguard (TradMG), or a VentMG. During each trial, subjects completed a modified maximal exercise test on a cycle ergometer and a series of physical agility tests (40-m dash, vertical leap, broad jump, 3-cone drill, and shuttle run). No differences were seen between control and the TradMG in any cardiorespiratory measures at any time during the maximal exercise test. Ventilation and blood lactate were lower (p ≤ 0.05) during VentMG at 200 W and at MAX; however, no differences in (Equation is included in full-text article.)were observed. Although TradMG had no impact on physical agility, VentMG produced a higher (1.9 cm; p = 0.03) vertical leap than control. Both mouthguard conditions negatively affected perceptions of breathability, comfort, and ability to communicate, but no differences existed between the 2 conditions. These findings confirm that TradMG has no negative impact on physiological function during exercise and physical agility; however, VentMG may have a positive impact at higher workload and on vertical leap.