Two independent lines of research propose that exertion of mental effort can impair subsequent performance due to ego depletion or mental fatigue. In this meta-analysis, we unite these research fields to facilitate a greater exchange between the two, to summarize the extant literature and to highlight open questions. We performed a meta-analysis to quantify the effect of ego-depletion and mental fatigue on subsequent physical endurance performance (42 independent effect sizes). We found that ego-depletion or mental fatigue leads to a reduction in subsequent physical endurance performance (ES = -0.506 [95% CI: -0.649, -0.369]) and that the duration of prior mental effort exertion did not predict the magnitude of subsequent performance impairment (r = -0.043). Further, analyses revealed that effects of prior mental exertion are more pronounced in subsequent tasks that use isolation tasks (e.g., handgrip; ES = -0.719 [-0.946, -0.493]) compared to whole-body endurance tasks (e.g. cycling; coefficient = 0.338 [0.057, 0.621]) and that the observed reduction in performance is higher when the person-situation fit is low (ES for high person-situation fit = -0.355 [-0.529, -0.181], coefficient for low person-situation fit = -0.336 [-0.599, -0.073]). Taken together, the aggregate of the published literature on ego depletion or mental fatigue indicates that prior mental exertion is detrimental to subsequent physical endurance performance. However, this analysis also highlights several open questions regarding the effects’ mechanisms and moderators. Particularly, the surprising finding that the duration of prior mental exertion seems to be unrelated to subsequent performance impairment needs to be addressed systematically.

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The effect of ego depletion or mental fatigue on subsequent physical endurance performance : A meta-analysis

Centala, J, Pogorel, C, Pummill, SW, and Malek, MH. Listening to fast-tempo music delays the onset of neuromuscular fatigue. J Strength Cond Res 34(3): 617-622, 2020-Studies determining the effect of music on physical performance have primarily focused on outcomes such as running time to exhaustion, blood lactate, or maximal oxygen uptake. The electromyographic fatigue threshold (EMGFT) is determined through a single incremental test and operationally defined as the highest exercise intensity that can be sustained indefinitely without an increase in EMG activity of the working muscle. To date, no studies have examined the role of fast-tempo music on EMGFT. The purpose of this investigation, therefore, was to determine whether fast-tempo music attenuates neuromuscular fatigue as measured by the EMGFT. We hypothesized that listening to fast-tempo music during exercise would increase the estimated EMGFT compared with the control condition. Secondarily, we hypothesized that maximal power output would also increase as a result of listening to fast-tempo music during the exercise workbout. Ten healthy college-aged men (mean ± SEM: age, 25.3 ± 0.8 years [range from 22 to 31 years]; body mass, 78.3 ± 1.8 kg; height: 1.77 ± 0.02 m) visited the laboratory on 2 occasions separated by 7 days. The EMGFT was determined from an incremental single-leg knee-extensor ergometer for each visit. In a randomized order, subjects either listened to music or no music for the 2 visits. All music was presented as instrumentals and randomized with a tempo ranging between 137 and 160 b·min. The results indicated that listening to fast-tempo music during exercise increased maximal power output (No Music: 48 ± 4; Music: 54 ± 3 W; p = 0.02) and EMGFT (No Music: 27 ± 3; Music: 34 ± 4 W; p = 0.008). There were, however, no significant mean differences between the 2 conditions (no music vs. music) for absolute and relative end-exercise heart rate as well as end-exercise rating of perceived exertion for the exercised leg. These findings suggest that listening to fast-tempo music increased overall exercise tolerance as well as the neuromuscular fatigue threshold. The results are applicable to both sport and rehabilitative settings.

Listening to Fast-Tempo Music Delays the Onset of Neuromuscular Fatigue

Studies examining the influence of priming, for continuous exercise, have mainly focused on improved exercise capacity related to oxygen uptake kinetics rather than on neuromuscular fatigue of the muscle. The purpose of this study, therefore, was to determine whether or not the electromyographic fatigue threshold (EMGFT) could be modulated by having subjects perform 2 incremental tests separated by 1 hour. We hypothesized that the EMGFT determined from the second incremental test would be higher than the EMGFT determined from the first incremental test. Nine healthy college-aged men (mean +/- SEM: age: 23.8 +/- 0.6 years; body mass: 79.5 +/- 3.3 kg; height: 1.78 +/- 0.02 m) were recruited from the university population. Each subject visited the laboratory on 1 occasion and performed 2 incremental single-leg knee-extensor ergometry to voluntary fatigue separated by 1 hour. The EMGFT was determined for each trial and statistically compared using paired-samples t-test. The results indicated significant mean differences between the EMGFT for the 2 trials (trial 1: 27 +/- 1 W vs. trial 2: 34 +/- 2 W; p = 0.001), whereas there were no significant mean differences for maximal power output (trial 1: 53 +/- 2 W vs. trial 2: 57 +/- 2; p = 0.09). These findings suggest that postactivation potentiation may, in part, explain the differences in EMGFT because the exercise mode used in the current study minimizes the cardiorespiratory responses to exercise.

Repeated Incremental Workbouts Separated by 1 Hour Increase the Electromyographic Fatigue Threshold.

Mental fatigue can be studied by using either the time-on-task protocol or the sequential task protocol. In the time-on-task protocol, participants perform a long and effortful task and a decrease in performance in this task is generally observed over time. In the sequential task protocol, a first effortful or control task is followed by a second effortful task. The performance in the second task is generally worse after the effortful task than after the control task. The principal aim of the present experiment is to examine the relationship between these two decrements in performance while concomitantly using a sequential task protocol and assessing the performance of the first effortful task as a function of time-on-task. We expect a positive correlation between these two decrements in performance. A total of 83 participants performed a 30-min fatiguing mental task (i.e., a modified Stroop task) or a control task followed by a time-to-exhaustion handgrip task. As expected, this protocol combining the time-on-task and sequential task protocols allowed us to observe (1) a decrease in performance over time during the Stroop task, (2) a worst performance in the handgrip task after the Stroop task by comparison to the control task, (3) a positive correlation between these two effects. The decrease in performance during the Stroop task also correlated with the subjective measures of boredom and fatigue, whereas the detrimental effect observed in the handgrip task did not. Our findings suggest that the two fatigue-related phenomena share a common mechanism but are not completely equivalent.

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A plausible link between the time-on-task effect and the sequential task effect

PURPOSE
Mental fatigue (MF) can impair physical performance in sport. We tested the hypothesis that cognitive load alone, and intermixed with standard resistance training, would induce MF, increase rating of perceived exertion (RPE), alter perception of weight lifting and training, and impair cycling time-trial performance.


METHODS
This 2-part study employed a within-participant design. In part 1, after establishing leg-extension 1-repetition maximum (1RM), 16 participants lifted and briefly held weights at 20%, 40%, 60%, and 80% of 1RM. RPE and electromyography (EMG) were measured for each lift. During the testing sessions, participants completed cognitive tasks (MF condition) or watched neutral videos (control condition) for 90 minutes before lifting the weights. In part 2, they completed submaximal resistance training comprising 6 weight training exercises followed by a 20-minute cycling time trial. In the MF condition, they completed cognitive tasks before and between weight training exercises. In the control condition, they watched neutral videos. Mood (Brunel Mood Scale), workload (National Aeronautics and Space Administration Task Load Index), MF-visual analogue scale (MF-VAS), RPE, psychomotor vigilance, distance cycled, power output, heart rate, and blood lactate were measured.


RESULTS
In part 1, the cognitive task increased lift-induced RPE (P = .011), increased MF-VAS (P = .002), and altered mood (P < .001) compared with control. EMG did not differ between conditions. In part 2, the cognitive tasks increased RPE (P < .001), MF-VAS (P < .001), and mental workload (P < .001), but reduced cycling time-trial power (P = .032) and distance (P = .023) compared with control. Heart rate and blood lactate did not differ between conditions.


CONCLUSION
A state of MF induced by cognitive load, alone or intermixed with physical load, increased RPE during weight lifting and training and impaired subsequent cycling performance.

Mental Fatigue: The Cost of Cognitive Loading on Weight Lifting, Resistance Training, and Cycling Performance.

Cognitive fatigue tasks performed before exercise may reduce exercise capacity. The electromyographic fatigue threshold (EMGFT) is the highest exercise intensity that can be maintained without significant increase in the electromyography (EMG) amplitude vs. time relationship. To date, no studies have examined the effect of cognitive fatigue on the estimation of the EMGFT. The purpose of this study, therefore, was to determine whether cognitive fatigue before performing exercise reduces the estimated EMGFT. Eight healthy college-aged men were recruited from a university student population and visited the laboratory on multiple occasions. In a randomized order, subjects performed either the cognitive fatigue task (AX continuous performance test) for 60 minutes on one visit (experimental condition) or watched a video on trains for 60 minutes on the other visit (control condition). After each condition, subjects performed the incremental single-leg knee-extensor ergometry test while the EMG amplitude was recorded from the rectus femoris muscle and heart rate was monitored throughout. Thereafter, the EMGFT was calculated for each subject for each visit and compared using paired samples t-test. For exercise outcomes, there were no significant mean differences for maximal power output between the 2 conditions (control: 51 +/- 5 vs. fatigue: 50 +/- 3 W), but there was a significant decrease in EMGFT between the 2 conditions (control: 31 +/- 3 vs. fatigue: 24 +/- 2 W; p = 0.013). Moreover, maximal heart rate was significantly different between the 2 conditions (control: 151 +/- 5 vs. fatigue: 132 +/- 6; p = 0.027). These results suggest that performing the cognitive fatiguing task reduces the EMGFT with a corresponding reduction in maximal heart rate response.

Justine R Ferris

Papers

Reduced Electromyographic Fatigue Threshold After Performing a Cognitive Fatiguing Task.