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Eduardo Macedo Penna, Edson Filho, Samuel Penna Wanner, Bruno Teobaldo Campos, Gabriel Resende Quinan, Thiago Teixeira Mendes, Mitchell Robert Smith and Luciano Sales Prado

Mental fatigue is conceptualized as a psychobiological state induced by sustained periods of demanding cognitive activity and characterized by feelings of tiredness and lack of energy ( 5 , 17 ). The adverse effects of mental fatigue on cognitive performance have been extensively reported ( 15 , 33

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Susan Vrijkotte, Romain Meeusen, Cloe Vandervaeren, Luk Buyse, Jeroen van Cutsem, Nathalie Pattyn and Bart Roelands

longer. 1 NFO and OTS are the result of a disbalance between training and recovery. Both psychological and physiological factors interact to create distress that can result in physical and mental fatigue. 2 Meeusen et al 1 , 3 developed a 2-bout exercise protocol for diagnosing NFO and OTS. The 2-bout

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Enzo Hollville, Vincent Le Croller, Yoshihiro Hirasawa, Rémi Husson, Giuseppe Rabita and Franck Brocherie

Internationale de Hockey’s rule changes). 1 The physical demands, therefore, require aerobic and anaerobic abilities combined with the aptitude to repeatedly execute technical skills (eg, passing and shooting) under pressure and while fatigued. Previous time–motion analysis studies have reported a decline in

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Oleg Verbitsky, Joseph Mizrahi, Arkady Voloshin, July Treiger and Eli Isakov

The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2 pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike–induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.

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Clare MacMahon, Linda Schücker, Norbert Hagemann and Bernd Strauss

This study investigated the effect of cognitive fatigue on physical performance in a paced running task. Experienced runners (n = 20) performed two 3,000-m runs on an indoor track, once after cognitive fatigue, and once under nonfatigued conditions. Completion times were significantly slower in the cognitive fatigue condition (M = 12:11,88 min, SD = 0:54,26), compared with the control condition (M = 11:58,56 min, SD = 0:48,39), F(1, 19) = 8.58, p = .009, eta2p = .31. There were no differences in heart rate, t(17) = 0.13, p > .05, blood lactate levels, t(19) = 1.19, p > .05, or ratings of perceived exertion F(1, 19) = .001, p 3 .05. While previous research has examined the impact of cognitive tasks on physical tasks, this is the first study to examine a self-paced physical task, showing that cognitive activity indeed contributes significantly to overall performance. Specifically, cognitive fatigue increased the perception of exertion, leading to lesser performance on the running task.

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Matt Jensen, Trent Stellingwerff and Marc Klimstra

The purpose was to determine the effect of carbohydrate (CHO) mouth rinse on maximal voluntary contraction (MVC) and neuromuscular output in a fatigued state. It was hypothesized that CHO mouth rinse would potentiate torque output in a fatigued state. In a double-blind, cross-over design, 12 competitive male athletes (9 rowers, 1 cyclist, 1 runner and 1 volleyball player) initially performed 3 × 5 s MVC isometric knee extensions followed by a 50% MVC contraction until volitional exhaustion, with quadriceps muscle activity measured via electromyography (EMG). Immediately after, either an 8% CHO maltodextrin (WASH), or noncaloric artificial sweetener (PLA) was mouth rinsed for 10sec, before 3 × 5 s final MVCs. Fatigue caused a significant decline in post fatigue MVC trial 1 for 3 s average torque (p = .03) and peak torque (p = .02) for PLA. This fatigue related decline in torque was not noticed for WASH, with a 2.5% and 3.5% less attenuation in peak and average torque, respectively in post fatigue MVC1 compared with PLA. The effect size for MVC trial 1 between WASH/PLA was seen to be small positive (ES = 0.22; 55% likelihood of positive). Overall for EMG RMS, there were no significant differences between PLA and WASH among all muscles. EMG median frequency showed comparable results between conditions with significant reductions due to fatigue. Taken together, this evidence suggests that the attenuation of torque post fatigue was less for CHO mouth rinse than a placebo. Even though the gains were marginal, these discoveries may play an important role in sport performance, as small performance effects can have significant outcomes in real-world competitions.

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Clayton L. Camic, Terry J. Housh, Jorge M. Zuniga, Haley C. Bergstrom, Richard J. Schmidt and Glen O. Johnson

The purpose of the current study was to examine the patterns of responses for torque, mechanomyographic (MMG) amplitude, MMG frequency, electromyographic (EMG) amplitude, and EMG frequency across 30 repeated maximal eccentric muscle actions of the leg extensors. Eleven moderately trained females performed an eccentric fatigue protocol at 30°/s with MMG and EMG signals recorded from the vastus lateralis. The results indicated there were significant (P < .05) decreases in MMG frequency (linear, r 2 = .395), EMG frequency (linear, r 2 = .177), and torque (linear, r 2 = .570; % decline = 9.8 ± 13.3%); increases in MMG amplitude (linear, r 2 = .783); and no change in EMG amplitude (r 2 = .003). These findings suggested that the neural strategies used to modulate torque during fatiguing eccentric muscle actions involved de-recruitment of motor units, reduced firing rates, and synchronization. In addition, the decreases in eccentric torque were more closely associated with changes in MMG frequency than EMG frequency. Thus, these findings indicated that MMG frequency, compared with EMG frequency, more accurately tracks fatigue during repeated maximal eccentric muscle actions.

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Michelle Smith Rockwell, Janet Walberg Rankin and Helen Dixon

This study investigated the effect of initial muscle glycogen on performance of repeated sprints and some potential mechanisms for an effect of glycogen on fatigue. Eight subjects performed 2 cycling trials (repeated 60-s sprints) following consumption of either a high carbohydrate (HC) or a low carbohydrate (LC) diet. Muscle biopsies and blood samples were collected at baseline, following a 15% (15% fatigue) and a 30% decline in sprint performance (30% fatigue), when exercise was terminated. Baseline muscle glycogen levels [346 ± 19 HC (SEM) vs. 222 ± 19 mmol/kg dw LC] and total exercise time to 30% fatigue were higher following HC than LC (57.5 ± 10.0 vs. 42.0 ± 3.6 min; p < .05). Similar significant (p < .05) decreases over the entire exercise bout were seen in muscle glycogen (43%), creatine phosphate (CP; 35%), and sarcoplasmic reticu-lum (SR) Ca2+-uptake in isolated homogenized muscle (56%) for both trials (p > .05 between trials). The percentage decline in SR Ca2+-release was less for HC than LC (36% and 53%, respectively), but this was not statistically different. In summary, HC delayed fatigue during repeated sprints. As the reductions in muscle glycogen, CP, and SR function during exercise were not different by dietary treatment, these data do not support a link between whole muscle glyco-gen and SR function or CP reduction during repeated sprint exercise.

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Gabriela Fischer, Jorge L.L. Storniolo and Leonardo A. Peyré-Tartaruga

The purpose of this study was to investigate the effects of acute fatigue on spring-mass model (SMM) parameters among recreational runners at different speeds. Eleven participants (5 males and 6 females) performed running trials at slower, self-selected, and faster speeds on an indoor track before and after performing a fatigue protocol (60 s of countermovement jumps). Maximal vertical force (Fmax), impact peak force (Fpeak), loading rate (LR), contact time (Tc), aerial time (Ta), step frequency (SF), step length (SL), maximal vertical displacement of the center of mass (ΔZ), vertical stiffness (Kvert), and leg work (Wleg) were measured using a force plate integrated into the track. A significant reduction (–43.1 ± 8.6%; P < .05) in mechanical power during jumps indicated that the subjects became fatigued. The results showed that under fatigue conditions, the runners adjusted their running mechanics at slower (≈2.7 ms–1; ΔZ –12% and SF +3.9%; P < .05), self-selected (≈3.3 ms–1; SF +3%, SL –6.8%, Ta –16%, and Fmax –3.3%; P < .05), and faster (≈3.6 ms–1 SL –6.9%, Ta –14% and Fpeak –9.8%; P < .05) speeds without significantly altering Kvert (P > .05). During constant running, the previous 60 s of maximal vertical jumps induced mechanical adjustments in the spatiotemporal parameters without altering Kvert.

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Yaara Nadiv, Ricki Vachbroit, Amit Gefen, David Elad, Uri Zaretsky, Dani Moran, Pinchas Halpern and Anat Ratnovsky

The respiratory muscles may fatigue during prolonged exercises and thereby become a factor that limits extreme physical activity. The aim of the current study was to determine whether respiratory muscle fatigue imposes a limitation on extreme physical activity of well-trained young men. Electromyography (EMG) signals of respiratory (external intercostal and sternomastoid) and calf muscles (gastrocnemius) were measured (N = 8) during 1 hr of treadmill marching at a speed of 8 km/hr with and without a 15 kg backpack. The root mean square (RMS) and the mean power frequency of the EMG signals were evaluated for calculating fatigue indices. The EMG RMS revealed that the respiratory and calf muscles did not fatigue during the marching without a backpack load. The study did show, however, a significant rise in the EMG values when a backpack was carried with respect to the no-load condition (p < .05), which suggests that respiratory muscles should be trained in military recruits who are required to carry loaded backpacks while marching.