The effect of mental fatigue on critical power during cycling exercise.

PURPOSE: Time to exhaustion (TTE) tests used in the determination of critical power (CP) and curvature constant (W') of the power-duration relationship are strongly influenced by the perception of effort (PE). This study aimed to investigate whether manipulation of the PE alters the CP and W'. METHODS: Eleven trained cyclists completed a series of TTE tests to establish CP and W' under two conditions, following a mentally fatiguing (MF), or a control (CON) task. Both cognitive tasks lasted 30 min followed by a TTE test. Ratings of PE and heart rate (HR) were measured during each TTE. Blood lactate was taken pre and post each TTE test. Ratings of perceived mental and physical fatigue were taken pre- and post-cognitive task, and following each TTE test. RESULTS: Perceived MF significantly increased as a result of the MF task compared to baseline and the CON task (P < 0.05), without a change in perceived physical fatigue (P > 0.05). PE was significantly higher during TTE in the MF condition (P < 0.05). Pre-post blood lactate accumulation was significantly lower after each TTE in MF condition (P < 0.05). HR was not significant different between conditions (P > 0.05). Neither cognitive task induced any change in CP (MF 253 ± 51 vs. CON 247 ± 58W; P > 0.05), although W' was significantly reduced in the MF condition (MF 22.8 ± 4.5 vs. CON 29.3 ± 6.3 kJ; P < 0.01). CONCLUSION: MF has no effect of CP, but reduces the W' in trained cyclists. Lower lactate accumulation during TTE tests following MF suggests that cyclists were not able to fully expend W' even though they exercised to volitional exhaustion.

Differential control of respiratory frequency and tidal volume during high-intensity interval training.

NEW FINDINGS: What is the central question of this study? By manipulating recovery intensity and exercise duration during high-intensity interval training (HIIT), we tested the hypothesis that fast inputs contribute more than metabolic stimuli to respiratory frequency (fR ) regulation. What is the main finding and its importance? Respiratory frequency, but not tidal volume, responded rapidly and in proportion to changes in workload during HIIT, and was dissociated from some markers of metabolic stimuli in response to both experimental manipulations, suggesting that fast inputs contribute more than metabolic stimuli to fR regulation. Differentiating between fR and tidal volume may help to unravel the mechanisms underlying exercise hyperpnoea. Given that respiratory frequency (fR ) has been proposed as a good marker of physical effort, furthering the understanding of how fR is regulated during exercise is of great importance. We manipulated recovery intensity and exercise duration during high-intensity interval training (HIIT) to test the hypothesis that fast inputs (including central command) contribute more than metabolic stimuli to fR regulation. Seven male cyclists performed an incremental test, a 10 and a 20 min continuous time trial (TT) as preliminary tests. Subsequently, recovery intensity and exercise duration were manipulated during HIIT (30 s work and 30 s active recovery) by performing four 10 min and one 20 min trial (recovery intensities of 85, 70, 55 and 30% of the 10 min TT mean workload; and 85% of the 20 min TT mean workload). The work intensity of the HIIT sessions was self-paced by participants to achieve the best performance possible. When manipulating recovery intensity, fR , but not tidal volume (VT ), showed a fast response to the alternation of the work and recovery phases, proportional to the extent of workload variations. No association between fR and gas exchange responses was observed. When manipulating exercise duration, fR and rating of perceived exertion were dissociated from VT , carbon dioxide output and oxygen uptake responses. Overall, the rating of perceived exertion was strongly correlated with fR (r = 0.87; P < 0.001) but not with VT . These findings may reveal a differential control of fR and VT during HIIT, with fast inputs appearing to contribute more than metabolic stimuli to fR regulation. Differentiating between fR and VT may help to unravel the mechanisms underlying exercise hyperpnoea.

Effects of caffeine on neuromuscular fatigue and performance during high-intensity cycling exercise in moderate hypoxia.

PURPOSE: To investigate the effects of caffeine on performance, neuromuscular fatigue and perception of effort during high-intensity cycling exercise in moderate hypoxia. METHODS: Seven adult male participants firstly underwent an incremental exercise test on a cycle ergometer in conditions of acute normobaric hypoxia (fraction inspired oxygen = 0.15) to establish peak power output (PPO). In the following two visits, they performed a time to exhaustion test (78 ± 3% PPO) in the same hypoxic conditions after caffeine ingestion (4 mg kg-1) and one after placebo ingestion in a double-blind, randomized, counterbalanced cross-over design. RESULTS: Caffeine significantly improved time to exhaustion by 12%. A significant decrease in subjective fatigue was found after caffeine consumption. Perception of effort and surface electromyographic signal amplitude of the vastus lateralis were lower and heart rate was higher in the caffeine condition when compared to placebo. However, caffeine did not reduce the peripheral and central fatigue induced by high-intensity cycling exercise in moderate hypoxia. CONCLUSION: The caffeine-induced improvement in time to exhaustion during high-intensity cycling exercise in moderate hypoxia seems to be mediated by a reduction in perception of effort, which occurs despite no reduction in neuromuscular fatigue.

Respiratory frequency is strongly associated with perceived exertion during time trials of different duration.

In order to provide further insight into the link between respiratory frequency (fR) and the rating of perceived exertion (RPE), the present study investigated the effect of exercise duration on perceptual and physiological responses during self-paced exercise. Nine well-trained competitive male cyclists (23 ± 3 years) performed a preliminary incremental ramp test and three randomised self-paced time trials (TTs) differing in exercise duration (10, 20 and 30 min). Both RPE and fR increased almost linearly over time, with a less-pronounced rate of increase when absolute exercise duration increased. However, when values were expressed against relative exercise duration, no between-trial differences were found in either RPE or fR. Conversely, between-trial differences were observed for minute ventilation (.VE), .VO2 and heart rate (HR), when values were expressed against relative exercise duration. Unlike the relationship between RPE and both .VE and HR, the relationship between RPE and fR was not affected by exercise duration. In conclusion, fR, but not .VE, HR or [.VO2, shows a strong relationship to RPE and a similar time course, irrespective of exercise duration. These findings indicate that fR is the best correlate of RPE during self-paced exercise, at least among the parameters and for the range of durations herein investigated.

Central alterations of neuromuscular function and feedback from group III-IV muscle afferents following exhaustive high-intensity one-leg dynamic exercise.

The aims of this investigation were to describe the central alterations of neuromuscular function induced by exhaustive high-intensity one-leg dynamic exercise (OLDE, study 1) and to indirectly quantify feedback from group III-IV muscle afferents via muscle occlusion (MO, study 2) in healthy adult male humans. We hypothesized that these central alterations and their recovery are associated with changes in afferent feedback. Both studies consisted of two time-to-exhaustion tests at 85% peak power output. In study 1, voluntary activation level (VAL), M-wave, cervicomedullary motor evoked potential (CMEP), motor evoked potential (MEP), and MEP cortical silent period (CSP) of the knee extensor muscles were measured. In study 2, mean arterial pressure (MAP) and leg muscle pain were measured during MO. Measurements were performed preexercise, at exhaustion, and after 3 min recovery. Compared with preexercise values, VAL was lower at exhaustion (-13 ± 13%, P < 0.05) and after 3 min of recovery (-6 ± 6%, P = 0.05). CMEP area/M area was lower at exhaustion (-38 ± 13%, P < 0.01) and recovered after 3 min. MEP area/M area was higher at exhaustion (+25 ± 27%, P < 0.01) and after 3 min of recovery (+17 ± 20%, P < 0.01). CSP was higher (+19 ± 9%, P < 0.01) only at exhaustion and recovered after 3 min. Markers of afferent feedback (MAP and leg muscle pain during MO) were significantly higher only at exhaustion. These findings suggest that the alterations in spinal excitability and CSP induced by high-intensity OLDE are associated with an increase in afferent feedback at exhaustion, whereas central fatigue does not fully recover even when significant afferent feedback is no longer present.

The effect of transcranial direct current stimulation of the motor cortex on exercise-induced pain.

PURPOSE: Transcranial direct current stimulation (tDCS) provides a new exciting means to investigate the role of the brain during exercise. However, this technique is not widely used in exercise science, with little known regarding effective electrode montages. This study investigated whether tDCS of the motor cortex (M1) would elicit an analgesic response to exercise-induced pain (EIP). METHODS: Nine participants completed a VO2max test and three time to exhaustion (TTE) tasks on separate days following either 10 min 2 mA tDCS of the M1, a sham or a control. Additionally, seven participants completed 3 cold pressor tests (CPT) following the same experimental conditions (tDCS, SHAM, CON). Using a well-established tDCS protocol, tDCS was delivered by placing the anodal electrode above the left M1 with the cathodal electrode above dorsolateral right prefrontal cortex. Gas exchange, blood lactate, EIP and ratings of perceived exertion (RPE) were monitored during the TTE test. Perceived pain was recorded during the CPT. RESULTS: During the TTE, no significant differences in time to exhaustion, RPE or EIP were found between conditions. However, during the CPT, perceived pain was significantly (P < 0.05) reduced in the tDCS condition (7.4 ± 1.2) compared with both the CON (8.6 ± 1.0) and SHAM (8.4 ± 1.3) conditions. CONCLUSION: These findings demonstrate that stimulation of the M1 using tDCS does not induce analgesia during exercise, suggesting that the processing of pain produced via classic measures of experimental pain (i.e., a CPT) is different to that of EIP. These results provide important methodological advancement in developing the use of tDCS in exercise.

Response inhibition impairs subsequent self-paced endurance performance.

PURPOSE: The aim of this study was to test the effects of mental exertion involving response inhibition on pacing and endurance performance during a subsequent 5-km running time trial. METHODS: After familiarization, 12 physically active subjects performed the time trial on a treadmill after two different cognitive tasks: (i) an incongruent Stroop task involving response inhibition (inhibition task) and (ii) a congruent Stroop task not involving response inhibition (control task). Both cognitive tasks were performed for 30 min. RESULTS: Neither the inhibition nor the control task induced subjective feelings of mental fatigue. Nevertheless, time trial performance was impaired following the inhibition task (24.4 ± 4.9 min) compared to the control task (23.1 ± 3.8 min) because of a significant reduction in average running speed chosen by the subject. The response inhibition task did not affect pacing strategy, which was negative in both conditions. Heart rate and blood lactate responses to the time trial were not affected by the inhibition task, but subjects rated perceived exertion higher compared to the control condition (13.5 ± 1.3 vs 12.4 ± 1.3). CONCLUSION: These findings show for the first time that 30 min of mental exertion involving response inhibition reduces subsequent self-paced endurance performance despite no overt mental fatigue. The impairment in endurance performance observed after the incongruent Stroop task seems to be mediated by the higher perception of effort as predicted by the psychobiological model of endurance performance.

Active mobility and mental health: A scoping review towards a healthier world.

Research has proven that engaging in active mobility (AM), namely walking and cycling for transportation, significantly enhances physical activity levels, leading to better physical health. It is still unclear whether AM could also offer any mental health benefits. This scoping review aims to provide a comprehensive understanding of the current knowledge on the relationship between AM and mental health, given its crucial role in public health. The authors searched online databases to isolate primary studies written in English involving an adult sample (16 or over). AM was the exposure factor. Many mental health elements were included as outcomes (depression, anxiety, self-esteem, self-efficacy, stress, psychological and subjective well-being, resilience, loneliness and social support, quality of life, mood, life satisfaction and sleep). The results were organised in a narrative summary per each outcome selected, graphical syntheses and an overview of gaps to be further examined. The authors identified a total of 55 papers as relevant. The results show inconsistency in study designs, definition and operationalisation of the variables, approach and methodologies used. A cross-sectional design was the dominant choice, primarily examining data from national public health surveys. Nonetheless, there has been improvement in outcomes of interests, initially mainly the quality of life and affect. Lately, authors have focused on a broader range of mental health-related factors (such as travel satisfaction). The experimental studies showed promising mental health improvements in those who used active modes more than those who used motorised vehicles. It creates a rationale for further research towards implementing a unified theoretical and methodological framework to study the link between AM and mental health. The ultimate goal is to generate solid conclusions that could support building societies and cities through public health promotion and sustainable strategies, like walking and cycling as a means of transport.

Effects of isolated locomotor muscle fatigue on pacing and time trial performance.

PURPOSE: Locomotor muscle fatigue impairs exercise performance during time to exhaustion tests. However, its effect on self-regulation of power output (pacing) is unknown. The primary aim of this study was to investigate the effects of locomotor muscle fatigue on pacing and time trial performance. METHODS: Ten healthy recreationally active men completed a 15-min time trial on a cycle ergometer 30 min after undergoing an eccentric fatiguing protocol designed to induce a substantial strength loss in the knee extensor muscles without inducing significant metabolic stress. This fatigue condition was compared with a control condition, using a randomly counterbalanced AB/BA crossover design. RESULTS: Total work completed during the 15-min cycling time trial was significantly reduced by 4.8 % in the fatigue condition compared with the control condition. This was caused by a significant reduction in power output. Rating of perceived exertion was significantly higher in the fatigue condition compared with the control condition only during the first 3 min of the time trial. Heart rate and vastus lateralis integrated electromyogram were not significantly different between the two conditions. CONCLUSION: The results show that participants with fatigued locomotor muscles reduce their pace but do not change their pacing strategy. As a result, there was a significant reduction in time trial performance. As predicted by the psychobiological model of exercise performance, a slower pace may be a behavioral response to compensate for the significant increase in perception of effort induced by locomotor muscle fatigue.

Pharmacological Blockade of Muscle Afferents and Perception of Effort: A Systematic Review with Meta-analysis.

BACKGROUND: The perception of effort provides information on task difficulty and influences physical exercise regulation and human behavior. This perception differs from other-exercise related perceptions such as pain. There is no consensus on the role of group III/IV muscle afferents as a signal processed by the brain to generate the perception of effort. OBJECTIVE: The aim of this meta-analysis was to investigate the effect of pharmacologically blocking muscle afferents on the perception of effort. METHODS: Six databases were searched to identify studies measuring the ratings of perceived effort during physical exercise, with and without pharmacological blockade of muscle afferents. Articles were coded based on the operational measurement used to distinguish studies in which perception of effort was assessed specifically (effort dissociated) or as a composite experience including other exercise-related perceptions (effort not dissociated). Articles that did not provide enough information for coding were assigned to the unclear group. RESULTS: The effort dissociated group (n = 6) demonstrated a slight increase in ratings of perceived effort with reduced muscle afferent feedback (standard mean change raw, 0.39; 95% confidence interval 0.13-0.64). The group effort not dissociated (n = 2) did not reveal conclusive results (standard mean change raw, - 0.29; 95% confidence interval - 2.39 to 1.8). The group unclear (n = 8) revealed a slight ratings of perceived effort decrease with reduced muscle afferent feedback (standard mean change raw, - 0.27; 95% confidence interval - 0.50 to - 0.04). CONCLUSIONS: The heterogeneity in results between groups reveals that the inclusion of perceptions other than effort in its rating influences the ratings of perceived effort reported by the participants. The absence of decreased ratings of perceived effort in the effort dissociated group suggests that muscle afferent feedback is not a sensory signal for the perception of effort.

Exertional fatigue in patients with CKD.

BACKGROUND: Fatigue is one of the most prevalent symptoms in chronic kidney disease (CKD). However, fatigue mechanisms are poorly understood due in part to nonspecific definitions. This study investigates exertional fatigue during simulated activities of daily living, focusing on oxygen delivery and utilization. STUDY DESIGN: "Explanatory" matched-cohort study. PARTICIPANTS & SETTING: 13 patients with CKD (stages 3b-4; mean age, 62 ± 13 [SD] years) and 13 healthy controls, mean matched for age, height, body mass and composition, and physical activity level. Participants completed an incremental cycle ergometer test to simulate energy expenditure of typical activities of daily living. FACTOR: 4 exercise intensities: 1, 1.8, 2.4, and 3.1 metabolic equivalent tasks (METs). OUTCOMES: The primary outcome was exertional fatigue by rating of perceived exertion (RPE) on a 6-20 scale. MEASUREMENTS: Other multidimensional measures of fatigue: UK Short Form Health Survey 36 (UK SF-36) Vitality and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) subscales. Physiologic measures of the oxygen transport and utilization chain (expired gas analysis, cardiac output, and arterial oxygen content) and blood lactate. RESULTS: RPE was increased in patients compared with controls at 2.4 (10.5 [ie, light] ± 2.7 vs 8.7 [very light] ± 1.7 units) and 3.1 (12.5 [somewhat hard] ± 2.6 vs 10.2 [light] ± 1.7 units) METs (interaction P = 0.03), which was consistent with higher chronic fatigue in patients by both the UK SF-36 Vitality (P = 0.01) and FACIT-Fatigue (P = 0.004) subscales. Arterial oxygen content was decreased in patients (P = 0.001), but cardiac output and oxygen extraction ratio were unchanged, decreasing oxygen delivery (P = 0.04). Respiratory exchange ratio (P = 0.004) and blood lactate production (P = 0.002) were increased. LIMITATIONS: Those inherent to a matched-cohort study. CONCLUSIONS: Using a novel application of the outcome measure RPE, patients with non-dialysis-dependent CKD reported considerable exertional fatigue during simulated activities of daily living. Poor compensation for mild anemia contributed to this symptom. In addition to anemia, the entire oxygen transport chain needs to be targeted to treat fatigue in patients with CKD.

Frowning muscle activity and perception of effort during constant-workload cycling.

We have recently demonstrated that electromyogram (EMG) amplitude of the frowning muscles correlates with perception of effort during leg-extension exercise. However, during aerobic exercise the relationship between facial EMG and perception of effort has never been investigated. The aim of the present study was to investigate whether facial EMG reflects perception of effort also during constant-workload cycling. We investigated the effects of exercise duration and exercise intensity on facial EMG of the corrugator supercilii muscles, rating of perceived effort, heart rate, and blood lactate concentration. Twenty recreationally active male and female volunteers performed a constant-workload time to exhaustion test on a cycle ergometer. Participants were randomly allocated to the heavy-intensity [63 ± 3% peak power output (P(peak))], or the severe-intensity (80 ± 5% P(peak)) group. The results show that facial EMG can differentiate between two exercise intensities during constant-workload cycling. The effects of exercise duration are inconclusive. Facial EMG increased over time in the severe-intensity group, but not in the heavy-intensity group. Future studies testing a wider range of exercise intensities are required to establish a correlation between facial EMG and exercise intensity during aerobic exercise, and further investigations are needed to establish why there is a discrepancy between facial EMG and perception of effort during lower-intensity aerobic exercise.

Development of a Revised Conceptual Framework of Physical Training for Use in Research and Practice.

A conceptual framework has a central role in the scientific process. Its purpose is to synthesize evidence, assist in understanding phenomena, inform future research and act as a reference operational guide in practical settings. We propose an updated conceptual framework intended to facilitate the validation and interpretation of physical training measures. This revised conceptual framework was constructed through a process of qualitative analysis involving a synthesis of the literature, analysis and integration with existing frameworks (Banister and PerPot models). We identified, expanded, and integrated four constructs that are important in the conceptualization of the process and outcomes of physical training. These are: (1) formal introduction of a new measurable component 'training effects', a higher-order construct resulting from the combined effect of four possible responses (acute and chronic, positive and negative); (2) explanation, clarification and examples of training effect measures such as performance, physiological, subjective and other measures (cognitive, biomechanical, etc.); (3) integration of the sport performance outcome continuum (from performance improvements to overtraining); (4) extension and definition of the network of linkages (uni and bidirectional) between individual and contextual factors and other constructs. Additionally, we provided constitutive and operational definitions, and examples of theoretical and practical applications of the framework. These include validation and conceptualization of constructs (e.g., performance readiness), and understanding of higher-order constructs, such as training tolerance, when monitoring training to adapt it to individual responses and effects. This proposed conceptual framework provides an overarching model that may help understand and guide the development, validation, implementation and interpretation of measures used for athlete monitoring.

Building a transdisciplinary expert consensus on the cognitive drivers of performance under pressure: An international multi-panel Delphi study.

Introduction: The ability to perform optimally under pressure is critical across many occupations, including the military, first responders, and competitive sport. Despite recognition that such performance depends on a range of cognitive factors, how common these factors are across performance domains remains unclear. The current study sought to integrate existing knowledge in the performance field in the form of a transdisciplinary expert consensus on the cognitive mechanisms that underlie performance under pressure. Methods: International experts were recruited from four performance domains [(i) Defense; (ii) Competitive Sport; (iii) Civilian High-stakes; and (iv) Performance Neuroscience]. Experts rated constructs from the Research Domain Criteria (RDoC) framework (and several expert-suggested constructs) across successive rounds, until all constructs reached consensus for inclusion or were eliminated. Finally, included constructs were ranked for their relative importance. Results: Sixty-eight experts completed the first Delphi round, with 94% of experts retained by the end of the Delphi process. The following 10 constructs reached consensus across all four panels (in order of overall ranking): (1) Attention; (2) Cognitive Control-Performance Monitoring; (3) Arousal and Regulatory Systems-Arousal; (4) Cognitive Control-Goal Selection, Updating, Representation, and Maintenance; (5) Cognitive Control-Response Selection and Inhibition/Suppression; (6) Working memory-Flexible Updating; (7) Working memory-Active Maintenance; (8) Perception and Understanding of Self-Self-knowledge; (9) Working memory-Interference Control, and (10) Expert-suggested-Shifting. Discussion: Our results identify a set of transdisciplinary neuroscience-informed constructs, validated through expert consensus. This expert consensus is critical to standardizing cognitive assessment and informing mechanism-targeted interventions in the broader field of human performance optimization.

High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals.

Continuous high glycemic load and inactivity challenge glucose homeostasis and fat oxidation. Hyperglycemia and high intramuscular glucose levels mediate insulin resistance, a precursor state of type 2 diabetes. The aim was to investigate whether a carbohydrate (CHO)-reduced diet combined with high-intensity interval training (HIIT) enhances the beneficial effects of the diet alone on insulin sensitivity and fat oxidation in obese individuals. Nineteen obese subjects underwent 14 days of CHO-reduced and energy-restricted diet. Ten of them combined the diet with HIIT (4 min bouts at 90% VO(2peak) up to 10 times, 3 times a week). Oral glucose insulin sensitivity (OGIS) increased significantly in both groups; [diet-exercise (DE) group: pre 377 ± 70, post 396 ± 68 mL min(-1) m(-2); diet (D) group: pre 365 ± 91, post 404 ± 87 mL min(-1) m(-2); P < 0.001]. Fasting respiratory exchange ratio (RER) decreased significantly in both groups (DE group: pre 0.91 ± 0.06, post 0.88 ± 0.06; D group: pre 0.92 ± 0.07, post 0.86 ± 0.07; P = 0.002). VO(2peak) increased significantly in the DE group (pre 27 ± 5, post 32 ± 6 mL kg(-1) min(-1); P < 0.001), but not in the D group (pre 26 ± 9, post 26 ± 8 mL kg(-1) min(-1)). Lean mass and resistin were preserved only in the DE group (P < 0.05). Fourteen days of CHO-reduced diet improved OGIS and fat oxidation (RER) in obese subjects. The energy-balanced HIIT did not further enhance these parameters, but increased aerobic capacity (VO(2peak)) and preserved lean mass and resistin.

The Effect of a Competitive Futsal Match on Psychomotor Vigilance in Referees.

CONTEXT: Referees' physical and cognitive performance are important for successful officiating in team sports. There is a lack of research on cognitive performance of referees in general, and none in futsal. PURPOSE: To assess referees' performance on the psychomotor vigilance task (PVT) before and after competitive futsal matches during the Football Association (FA) National Futsal League 2015/16. METHODS: Fourteen futsal referees (mean [SD] age 34.3 [10.0] y) from the FA National Futsal group were included. The referees were required to undertake a 10-min PVT 60 min before the match kickoff time (pretest) and immediately after matches (posttest). They also completed the Brunel Mood Scale (BRUMS) questionnaire before the prematch PVT and after the postmatch PVT. RESULT: Data were analyzed by paired t tests comparing prematch and postmatch results. There was a significant difference in BRUMS parameters vigor (9.5 [2.5] prematch vs 6.3 [2.4] postmatch, P = .001) and fatigue (1.4 [1.3] prematch vs 5.6 [3.1] postmatch, P < .001). However, PVT performance was significantly improved (mean reaction time 248.3 [26.2] ms prematch vs 239.7 [22.4] ms postmatch, P = .023). CONCLUSIONS: The present results show, contrary to the authors' initial hypothesis, that psychomotor performance is improved as opposed to decreased after a single match. The postmatch improvement suggests that exercise can acutely enhance cognitive performance, which could be used to inform warm-up practices (eg, optimal duration and intensity) geared toward optimizing referees' cognitive performance during matches.

Mental fatigue impairs physical performance in humans.

Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated. In this randomized crossover study, 16 subjects cycled to exhaustion at 80% of their peak power output after 90 min of a demanding cognitive task (mental fatigue) or 90 min of watching emotionally neutral documentaries (control). After experimental treatment, a mood questionnaire revealed a state of mental fatigue (P = 0.005) that significantly reduced time to exhaustion (640 +/- 316 s) compared with the control condition (754 +/- 339 s) (P = 0.003). This negative effect was not mediated by cardiorespiratory and musculoenergetic factors as physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. However, mentally fatigued subjects rated perception of effort during exercise to be significantly higher compared with the control condition (P = 0.007). As ratings of perceived exertion increased similarly over time in both conditions (P < 0.001), mentally fatigued subjects reached their maximal level of perceived exertion and disengaged from the physical task earlier than in the control condition. In conclusion, our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms. Future research in this area should investigate the common neurocognitive resources shared by physical and mental activity.

Heart rate and blood lactate correlates of perceived exertion during small-sided soccer games.

The rating of perceived exertion (RPE) could be a practical measure of global exercise intensity in team sports. The purpose of this study was to examine the relationship between heart rate (%HR(peak)) and blood lactate ([BLa(-)]) measures of exercise intensity with each player's RPE during soccer-specific aerobic exercises. Mean individual %HR(peak), [BLa(-)] and RPE (Borg's CR 10-scale) were recorded from 20 amateur soccer players from 67 soccer-specific small-sided games training sessions over an entire competitive season. The small-sided games were performed in three 4min bouts separated with 3min recovery on various sized pitches and involved 3-, 4-, 5-, or 6-players on each side. A stepwise linear multiple regression was used to determine a predictive equation to estimate global RPE for small-sided games from [BLa(-)] and %HR(peak). Partial correlation coefficients were also calculated to assess the relationship between RPE, [BLa(-)] and %HR(peak). Stepwise multiple regression analysis revealed that 43.1% of the adjusted variance in RPE could be explained by HR alone. The addition of [BLa(-)] data to the prediction equation allowed for 57.8% of the adjusted variance in RPE to be predicted (Y=-9.49-0.152 %HR(peak)+1.82 [BLa(-)], p<0.001). These results show that the combination of [BLa(-)] and %HR(peak) measures during small-sided games is better related to RPE than either %HR(peak) or [BLa(-)] measures alone. These results provide further support the use of RPE as a measure of global exercise intensity in soccer.

Internal and External Training Load: 15 Years On.

Exercise is a stressor that induces various psychophysiological responses, which mediate cellular adaptations in many organ systems. To maximize this adaptive response, coaches and scientists need to control the stress applied to the athlete at the individual level. To achieve this, precise control and manipulation of the training load are required. In 2003, the authors introduced a theoretical framework to define and conceptualize the measurable constructs of the training process. They described training load as having 2 measurable components: internal and external load. The aim of this commentary is to extend, clarify, and refine both the theoretical framework and the definitions of internal and external training load to avoid misinterpretation of this concept.

Comparing the Effects of Three Cognitive Tasks on Indicators of Mental Fatigue.

This investigation assessed the impact of three cognitively demanding tasks on cognitive performance, subjective, and physiological indicators of mental fatigue. Following familiarization, participants completed four testing sessions, separated by 48 h. During each session, participants watched a 45-min emotionally neutral documentary (control) or completed one of the following computer tasks: Psychomotor Vigilance Task (PVT); AX-Continuous Performance Test (AX-CPT); or Stroop Task. Mental fatigue was assessed before and at regular periods for 60 min following the 45-min treatments. Cognitive performance was assessed using 3-min PVT, and task performance. Subjective assessments were conducted using the Brunel Mood Scale, and visual analog scales (VAS). Physiological indicators of mental fatigue included electroencephalography (EEG), and heart rate variability (HRV). Subjective ratings of mental fatigue increased from pre to 0-min post in all-treatments, but not the documentary (p < 0.05). Subjective fatigue (VAS) remained higher (p < 0.05) than pretreatment values for 20-, 50-, and 60-min following the PVT, Stroop, and AX-CPT respectively. The cognitively demanding tasks had unclear effects on 3-min PVT, EEG, and HRV assessments. Tasks requiring response inhibition appear to induce fatigue for longer durations than a simple vigilance task. Simple VAS appear to be the most practical method for assessing mental fatigue.