A drop in cognitive performance, whodunit? Subjective mental fatigue, brain deactivation or increased parasympathetic activity? It's complicated!

INTRODUCTION: The discussion on the mechanism(s) underlying mental fatigue is still ongoing. We want to reconfirm a performance-impairing effect of executing a lengthy cognitive task on the subsequent task, and determine how this effect is subtended by neurophysiological variations and subjective experience. METHODS: Twenty participants (12 females; age: 23 ± 1 y) performed an experimental (EXP) and a control trial (CON) in a randomized counter-balanced order. In both trials a 90-min cognitive task had to be performed (EXP, Stroop task; CON, documentary), that was preceded and followed up by a 10-min flanker task that was completed in the MRI scanner. Throughout the protocol, subjective self-evaluation, peripheral autonomic activation and metabolic measures, cognitive performance and functional brain imagery were recorded. Due to equipment issues, only 11 participants could be included in the analysis of the peripheral autonomic activation. RESULTS: Flanker performance dropped both in EXP and CON (p = .010). Heart rate variability increased in time, both in EXP and CON (p ≤ .047). A time-on-task related drop in Stroop performance (p = .007) and higher subjective mental fatigue was observed in EXP compared to CON (p < .001). Moreover, the BOLD signal of response inhibition-associated brain activity in corpus callosum, somatosensory association cortex and anterior cingulate cortex was reduced during the post-flanker task in EXP compared to CON (p < .001). Discussion Our results indicate two different processes: 1) A time-on-task effect as a peripheral physiological deactivation that coincided with the observed post-flanker performance drop both in EXP and CON; and 2) An increase in the level of subjective mental fatigue with prolonged performance on a 90-min Stroop task that is associated with a decrease in response inhibition-associated brain activity in both grey and white matter, specifically in the EXP-condition. CONCLUSION: Our results highlight the multifactoriality of carryover effects, in the present study increased parasympathetic activity was linked with the drop in performance.

Can Creatine Combat the Mental Fatigue-associated Decrease in Visuomotor Skills?

PURPOSE: The importance of the brain in sports was recently confirmed by the negative effect of mental fatigue (MF) on sport-specific psychomotor skills. Creatine supplementation improves strength but can also improve cognitive functioning. To explore the role of creatine in combating MF, we evaluated whether creatine supplementation counteracts the MF-associated impairment in sport-specific psychomotor skills. METHODS: In 23°C, 14 healthy participants (4 females, 10 males; mean ± SD, age = 24 ± 3 yr, mass = 74 ± 13 kg, height = 179 ± 9 cm) performed a 90-min mentally fatiguing task (counterbalanced, crossover, and double-blinded; i.e., Stroop task) in two different conditions: after a 7-d creatine supplementation (CR; 20 g·d) and after a 7-d calcium lactate supplementation (placebo [PLAC]), separated by a 5-wk washout. In both conditions, a 7-min sport-specific visuomotor task, a dynamic handgrip strength endurance task, and a 3-min Flanker task was performed before and after the mentally fatiguing task. Physiological and perceptual responses were measured throughout the protocol. RESULTS: Handgrip strength endurance was higher in CR compared with PLAC (P = 0.022). MF impaired visuomotor response time (+4.4%; P = 0.022) and Flanker accuracy (-5.0%; P = 0.009) in both conditions. Accuracy on the Stroop task was higher in CR compared with PLAC (+4.9%; P = 0.026). Within the perceptual and physiological parameters, only motivation and vigor (P ≤ 0.027) were lower in CR compared with PLAC. CONCLUSION: Creatine supplementation improved physical (strength endurance) and prolonged cognitive (Stroop accuracy) performance, yet it did not combat MF-induced impairments in short sport-specific psychomotor or cognitive (Flanker) performance. These results warrant further investigation in the potential role of creatine in combating the MF-associated decrements in prolonged (e.g., 90-min soccer game) sport performance and suggest a role of brain phosphocreatine in MF.

IOC consensus statement: dietary supplements and the high-performance athlete.

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition programme. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including (1) the management of micronutrient deficiencies, (2) supply of convenient forms of energy and macronutrients, and (3) provision of direct benefits to performance or (4) indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can benefit the athlete, but others may harm the athlete's health, performance, and/or livelihood and reputation (if an antidoping rule violation results). A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome and habitual diet. Supplements intended to enhance performance should be thoroughly trialled in training or simulated competition before being used in competition. Inadvertent ingestion of substances prohibited under the antidoping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete's health and awareness of the potential for harm must be paramount; expert professional opinion and assistance is strongly advised before an athlete embarks on supplement use.

IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete.

Nutrition usually makes a small but potentially valuable contribution to successful performance in elite athletes, and dietary supplements can make a minor contribution to this nutrition program. Nonetheless, supplement use is widespread at all levels of sport. Products described as supplements target different issues, including the management of micronutrient deficiencies, supply of convenient forms of energy and macronutrients, and provision of direct benefits to performance or indirect benefits such as supporting intense training regimens. The appropriate use of some supplements can offer benefits to the athlete, but others may be harmful to the athlete's health, performance, and/or livelihood and reputation if an anti-doping rule violation results. A complete nutritional assessment should be undertaken before decisions regarding supplement use are made. Supplements claiming to directly or indirectly enhance performance are typically the largest group of products marketed to athletes, but only a few (including caffeine, creatine, specific buffering agents and nitrate) have good evidence of benefits. However, responses are affected by the scenario of use and may vary widely between individuals because of factors that include genetics, the microbiome, and habitual diet. Supplements intended to enhance performance should be thoroughly trialed in training or simulated competition before implementation in competition. Inadvertent ingestion of substances prohibited under the anti-doping codes that govern elite sport is a known risk of taking some supplements. Protection of the athlete's health and awareness of the potential for harm must be paramount, and expert professional opinion and assistance is strongly advised before embarking on supplement use.

Nutritional Supplements and the Brain.

Cognitive function plays an important role in athletic performance, and it seems that brain functioning can be influenced by nutrition and dietary components. Thus, the central nervous system might be manipulated through changes in diet or supplementation with specific nutrients including branched-chain amino acids, tyrosine, carbohydrates, and caffeine. Despite some evidence that branched-chained amino acids can influence ratings of perceived exertion and mental performance, several well-controlled studies have failed to demonstrate a positive effect on exercise performance. Evidence of an ergogenic benefit of tyrosine supplementation during prolonged exercise is limited. There is evidence that mild dehydration can impair cognitive performance and mood. The beneficial effect of carbohydrate supplementation during prolonged exercise could relate to increased substrate delivery for the brain, with numerous studies indicating that hypoglycemia affects brain function and cognitive performance. Caffeine can enhance performance and reduce perception of effort during prolonged exercise and will influence specific reward centers of the brain. Plant products and herbal extracts such as polyphenols, ginseng, ginkgo biloba, etc. are marketed as supplements to enhance performance. In several animal studies, positive effects of these products were shown, however the literature on their effects on sports performance is scarce. Polyphenols have the potential to protect neurons against injury induced by neurotoxins, suppress neuroinflammation, and to promote memory, learning, and cognitive function. In general, there remains a need for controlled randomized studies with a strong design, sufficient statistical power, and well-defined outcome measures before "claims" on its beneficial effects on brain functioning can be established.

Sleep during an Antarctic summer expedition: new light on "polar insomnia".

Sleep complaints are consistently cited as the most prominent health and well-being problem in Arctic and Antarctic expeditions, without clear evidence to identify the causal mechanisms. The present investigation aimed at studying sleep and determining circadian regulation and mood during a 4-mo Antarctic summer expedition. All data collection was performed during the continuous illumination of the Antarctic summer. After an habituation night and acclimatization to the environment (3 wk), ambulatory polysomnography (PSG) was performed in 21 healthy male subjects, free of medication. An 18-h profile (saliva sampling every 2 h) of cortisol and melatonin was assessed. Mood, sleepiness, and subjective sleep quality were assessed, and the psychomotor vigilance task was administered. PSG showed, in addition to high sleep fragmentation, a major decrease in slow-wave sleep (SWS) and an increase in stage R sleep. Furthermore, the ultradian rhythmicity of sleep was altered, with SWS occurring mainly at the end of the night and stage R sleep at the beginning. Cortisol secretion profiles were normal; melatonin secretion, however, showed a severe phase delay. There were no mood alterations according to the Profile of Mood States scores, but the psychomotor vigilance test showed an impaired vigilance performance. These results confirm previous reports on "polar insomnia", the decrease in SWS, and present novel insight, the disturbed ultradian sleep structure. A hypothesis is formulated linking the prolonged SWS latency to the phase delay in melatonin.NEW & NOTEWORTHY The present paper presents a rare body of work on sleep and sleep wake regulation in the extreme environment of an Antarctic expedition, documenting the effects of constant illumination on sleep, mood, and chronobiology. For applied research, these results suggest the potential efficiency of melatonin supplementation in similar deployments. For fundamental research, these results warrant further investigation of the potential link between melatonin secretion and the onset of slow-wave sleep.

Caffeine, exercise and the brain.

Caffeine can improve exercise performance when it is ingested at moderate doses (3-6 mg/kg body mass). Caffeine also has an effect on the central nervous system (CNS), and it is now recognized that most of the performance-enhancing effect of caffeine is accomplished through the antagonism of the adenosine receptors, influencing the dopaminergic and other neurotransmitter systems. Adenosine and dopamine interact in the brain, and this might be one mechanism to explain how the important components of motivation (i.e. vigor, persistence and work output) and higher-order brain processes are involved in motor control. Caffeine maintains a higher dopamine concentration especially in those brain areas linked with 'attention'. Through this neurochemical interaction, caffeine improves sustained attention, vigilance, and reduces symptoms of fatigue. Other aspects that are localized in the CNS are a reduction in skeletal muscle pain and force sensation, leading to a reduction in perception of effort during exercise and therefore influencing the motivational factors to sustain effort during exercise. Because not all CNS aspects have been examined in detail, one should consider that a placebo effect may also be present. Overall, it appears that the performance-enhancing effects of caffeine reside in the brain, although more research is necessary to reveal the exact mechanisms through which the CNS effect is established.

Effects of noradrenaline and dopamine on supraspinal fatigue in well-trained men.

PURPOSE: Prolonged exhaustive exercise induces a failure of the nervous system to activate the involved muscles maximally (i.e., central fatigue). Part of central fatigue may reflect insufficient output from the motor cortex (i.e., supraspinal fatigue), but the cause is unresolved. To investigate the potential link between supraspinal fatigue and changes in brain concentration of dopamine and noradrenaline in temperate environment, we combined neurophysiological methods and pharmacological manipulation of these two neurotransmitters. METHODS: Changes in performance of a cycling exercise (time trial [TT]) were tested after oral administration of placebo (Pla), dopamine, or noradrenaline reuptake inhibitors (methylphenidate and reboxetine [Rebox], respectively) in well-trained male subjects. Changes in voluntary activation, corticospinal excitability, and muscle contractile properties were tested in the knee extensors using transcranial magnetic stimulation and motor nerve electrical stimulation before and after exercise. A psychomotor vigilance task (PVT) was also performed. RESULTS: Compared with Pla, methylphenidate did not affect exercise performance (P = 0.19), but more time was needed to complete the TT after administration of Rebox (approximately 9%, P < 0.05). For the latter condition, the reduced performance was accompanied by a central/supraspinal fatigue (5%-6%, P < 0.05) and worsened PVT performance (7%, P < 0.05). For the three conditions, corticospinal excitability was unchanged, and peripheral fatigue was similar. Because the ingestion of Rebox induced a greater decrease in voluntary activation and PVT performance after the TT than Pla, with no modification in corticospinal excitability, the noradrenaline reuptake inhibitor likely affected supraspinal circuits located before the motor cortex. CONCLUSION: These results suggest that noradrenaline, but not dopamine reuptake inhibition, contributes to the development of central/supraspinal fatigue after a prolonged cycling exercise performed in temperate conditions.

Continuous monitoring of hypothalamic neurotransmitters and thermoregulatory responses in exercising rats.

The purpose of the present study was to investigate the relationship between thermoregulation and catecholamine release in the preoptic area and anterior hypothalamus (PO/AH) during incremental treadmill running in the rat. To this aim, we combined in vivo brain microdialysis, biotelemetry and metabolic measurements for continuous monitoring of core body temperature (T(core)), neurotransmitters and thermoregulatory responses. The animals were exercised for 1h at 23°C. Treadmill speed was increased every 20 min (10, 20 and 26 m min⁻¹). T(core), oxygen consumption (V˙O2, an index of heat production) and tail skin temperature (T(tail), an index of heat loss) were simultaneously measured. Brain microdialysis samples were collected every 10 min, and these samples were analyzed for noradrenaline (NA), dopamine (DA) and serotonin (5-HT). T(core) and V˙O(2)2 significantly increased during treadmill and were exercise intensity dependent. After an initial drop T(tail) increased significantly during exercise. Both NA and DA levels in the PO/AH increased significantly during exercise. There was no effect on serotonin release. T(core), V˙O2 and T(tail) were positively correlated with the levels of NA and DA. Our data suggest that thermoregulatory responses are dependent on the intensity of the exercise and that these responses are associated with changes in NA and DA release, but not in 5-HT release in the PO/AH.

Effectiveness of active versus passive recovery strategies after futsal games.

This study aimed to investigate the effects of immediate postgame recovery interventions (seated rest, supine electrostimulation, low-intensity land exercises, and water exercises) on anaerobic performance (countermovement jump [CMJ], bounce jumping, 10-m sprint), hormones (salivary cortisol, urinary catecholamines), and subjective ratings (rate of perceived exertion [RPE], leg muscle pain, Questionnaire of Recovery Stress for Athletes [RestQ Sport], 10-point Likert scale), and hours of sleep of futsal players. Heart rate (HR), blood lactate, and RPE were used to evaluate the intensity of 4 futsal games in 10 players using a crossover design (P < 0.05), randomly allocating athletes to 1 of the 4 recovery interventions at the end of each game. No significant difference emerged between HR, blood lactate, RPE, and level of hydration of the games. A significant difference (P < 0.001) between games emerged for total urinary catecholamines, with an increase from the first to the second game and a gradual reduction up to the fourth game. After the game, significant reductions in CMJ (P < 0.001) and 10-m sprints (P < 0.05) emerged. No significant difference was found between recovery interventions for anaerobic performances, hormones, muscle pain, and RestQ Sport. Even though a well-balanced diet, rehydration, and controlled lifestyle might represent a sufficient recovery intervention in young elite athletes, the players perceived significantly increased benefit (P < 0.01) from the electrostimulation (7.8 +/- 1.4 points) and water exercises (7.6 +/- 2.1 points) compared to dry exercises (6.6 +/- 1.8 points) and seated rest (5.2 +/- 0.8 points.), which might improve their attitude toward playing. To induce progressive hormonal adaptation to the high exercise load of multiple games, in the last 2 weeks of the preseason, coaches should organize friendly games at a level similar to that of the competitive season.

Brain neurotransmitters in fatigue and overtraining.

Since the publication of the serotonin hypothesis, numerous theories involving the accumulation or depletion of different substances in the brain have been proposed to explain central fatigue. Although the theoretical rationale for the "serotonin-fatigue hypothesis" is clear, several seemingly well-conducted studies have failed to support a significant role for 5-hydroxytryptamine in the development of fatigue. As brain function appears to be dependent upon the interaction of a number of systems, it is unlikely that a single neurotransmitter system is responsible for central fatigue. Several other mechanisms are involved, with evidence supporting a role for the brain catecholamines. Fatigue is therefore probably an integrated phenomenon, with complex interaction among central and peripheral factors. When prolonged and excessive training happens, concurrent with other stressors and insufficient recovery, performance decrements can result in chronic maladaptations that can lead to the overtraining syndrome (OTS). The mechanism of the OTS could be difficult to examine in detail, perhaps because the stress caused by excessive training load, in combination with other stressors, might trigger different "defence mechanisms" such as the immunological, neuroendocrine, and other physiological systems that all interact and probably therefore cannot be pinpointed as the "sole" cause of the OTS. It might be that, as in other syndromes, the psychoneuroimmunology (study of brain-behavior-immune interrelationships) might shed a light on the possible mechanisms of the OTS, but until there is a definite diagnostic tool, it is of utmost importance to standardize measures that are now thought to provide a good inventory of the training status of the athlete. It is very important to emphasize the need to distinguish the OTS from overreaching and other potential causes of temporary underperformance such as anemia, acute infection, muscle damage, and insufficient carbohydrate intake.

Effects of different recovery interventions on anaerobic performances following preseason soccer training.

In the preseason soccer training, morning and afternoon training sessions often are scheduled daily. The high frequency of training sessions could place heavy strain on biological systems, and it is necessary to apply proper recovery strategies for improving the players' capability to regain an adequate working state for subsequent training units. However, the effect of recovery interventions following soccer training units is debatable, due to a lack of studies performed in field situations. The aim of this study was to examine, during a 21-day preseason soccer training, the most effective recovery intervention (i.e., passive, dry-aerobic exercises, water-aerobic exercises, electrostimulation) on anaerobic performances (i.e., squat jump, countermovement jump, bounce jumping, and 10-m sprint) and subjective ratings (i.e., perceived exertion and muscle pain), with the conditions before the intervention controlled and standardized. Twelve young (age: 18.1 +/- 1.2 years) elite soccer players participated. Data were collected on 4 occasions 2 days apart and at the same time of the day. Activity and dietary intake were replicated on each occasion. After baseline measurements, participants performed a standardized training during which their heart rates and ratings of perceived exertion were recorded. This was followed by a 20-minute recovery intervention. After a 5-hour rest, athletes' ratings of muscle pain were recorded prior to a second test session. There were no significant differences in exercise intensities and baseline anaerobic performances. Significantly (p < 0.01) better performances were observed in the afternoon. Although no main effect of recovery intervention was observed on anaerobic performances, dry-aerobic exercises (0.6 +/- 0.9) and electrostimulation (0.6 +/- 1.2) were more beneficial (p < 0.01) than water-aerobic exercises (2.1 +/- 1.1) and passive rest (2.1 +/- 1.7) for reducing muscle pain, which could affect the player's working ability.

Validity of the new Backache Index (BAI) in patients with low back pain.

BACKGROUND CONTEXT: The Backache Index (BAI) is applied to patients with low back pain (LBP) in order to help therapists, doctors, and surgeons perform physical examinations easily. It is carried out within a short space of time (<2 min) without using inclinometric instruments. PURPOSE: To explore the reliability, validity, and responsiveness of this new Backache Index in patients with LBP, which can fulfil the existing need for a reliable routine examination in the clinical environment. STUDY DESIGN/SETTING: Patients with LBP filled in disability questionnaires; pain rating scales and physical impairment tests were completed in function of construct validity and correlation studies. A subgroup was evaluated for interobserver and test-retest reliability, and a second group was reassessed after two active treatment sessions to verify the responsiveness compared with other examined variables. PATIENT SAMPLE: In total, 75 patients with subacute LBP (3-12 weeks) participated in a randomized controlled study. OUTCOME MEASURES: The validity of the BAI was explored through a correlation with the standard Oswestry LBP Disability Index (ODI), the McGill LBP Questionnaire Index (MPQ), and the Visual Analogue Scale (VAS). METHODS: The BAI consisted of a scoring system that includes pain factors and stiffness estimation at the end of a series of five different lumbar movements of a patient standing in an erect position. RESULTS: The correlations between the separate outcomes and the BAI ranged from 0.61 to 0.76 (p<.001). The interobserver reliability between two experienced observers for the five outcome scores was good (intraclass correlation coefficient [ICC]>0.86) and even perfect for the BAI (ICC=0.96). A BAI change of one unit is able to exclude a measurement error. A significantly good correlation (p<.001) was found between the BAI at baseline, the ODI (R=0.62), and the total degree of pain rating index (MPQ-PRI-T) (R=0.57), a moderate correlation with the total number of chosen adjectives from the whole list of adjectives (MPQ-NWC-T) (R=0.48), and the VAS (R=0.47), but a lower correlation was found with the MPQ-Quality of life index (R=0.43). The effect size and discriminative ability of the measures were explored after two treatment sessions of deep transverse friction myotherapy by means of study of the receiver operating characteristics curve (ROC) and the greatest area under the curve (AUC). The greatest level of distinction was found for the MPQ-PRI-T and the BAI (AUC>0.93), followed by the ODI (AUC=0.92). A lower level of distinction was found for the MPQ-NWC-T and the VAS (AUC>0.82). CONCLUSIONS: The BAI appears to be a reliable and valid assessment of overall restricted spinal movements in case of LBP and discriminates between successful and unsuccessful treatment outcome.