Performance and thermoregulatory effects of chronic bupropion administration in the heat

Depressive Disorders in Athletes

Depressive disorders in athletes are thought to be at least as common as the general population. However, athletes have a unique set of risk factors that can affect the likelihood of developing depression. Screening tools have been developed specifically for athletes such as the Sport Mental Health Assessment Tool (SMHAT). The management of the depressed athlete should involve an individualized approach, with methods such as counseling, interpersonal therapy, or cognitive behavioral therapy being used. Some may require antidepressant medication. Depressive disorders are also linked to sucidality in athletes, and the team physician and sporting organisation should have a crisis management plan in place for mental health emergencies. Tackling the stigma that remains in sport is a key part to improving mental wellbeing for all athletes.

ADHD Prescription Medications and Their Effect on Athletic Performance: A Systematic Review and Meta-analysis

BACKGROUND

Stimulant medications used for the treatment of Attention Deficit-Hyperactivity Disorder (ADHD) are believed to provide a physical advantage in athletics, but several of these medications are not regulated by the World Anti-Doping Association. Given the prevalence of ADHD among the athlete population and concern for abuse of ADHD medications, this review and meta-analysis aimed to evaluate effects of ADHD medications on athletic performance, thereby appraising the validity of claims of performance enhancement.

METHODS

A search of MEDLINE, Embase, CINAHL, and Cochrane Review databases was performed for all randomized controlled trials evaluating athletic performance after ingestion of placebo or ADHD treatment medications from August 2020 through November 2020. All RCTs identified from these search criteria were included for screening, with exclusion of any animal studies. Two reviewers (JB, CK) assessed methodological quality and risk of bias using CONSORT 2010 and Cochrane Collaboration tools. Study results were compiled with corresponding p values for each finding. Effect sizes (Cohen's D) for athletic performance and physiological changes were aggregated for each study. Studies were further screened for homogeneity that would allow for meta-analysis. Heterogeneity was calculated using I2.

RESULTS

A total of 13,033 abstracts evaluating amphetamine, methamphetamine, methylphenidate, and bupropion were screened. The final analysis included nine studies, six of which found significant improvement in athletic performance with use of stimulant medications (p < 0.05). Methylphenidate and amphetamine were consistently identified to have a performance effect. Secondary effects identified included significant increase in heart rate, core temperature, and elevation of various serum hormone levels (p < 0.05). Effect size evaluation found seven studies demonstrating small to large effects on physical performance, as well as in categories of cardiometabolic, temperature, hormone, and ratings of perceived exertion, to varying degrees. A meta-analysis was performed on two studies, demonstrating conflicting results.

CONCLUSIONS

Dopaminergic/noradrenergic agonist medications appear to have a positive effect on athletic performance, as well as effects on physiological parameters. Further consideration of medications currently not regulated, i.e. bupropion, is warranted given evidence of athletic performance enhancement. PROSPERO trial registration number: CRD42020211062; 10/29/2020 retrospectively registered.

Psychiatric medication and physical performance parameters - Are there implications for treatment?

INTRODUCTION

The impact of psychiatric medications and their enhancing or impairing effects on physical performance remains inconclusive. Therefore, with this systematic review we provide a comprehensive overview of frequently used psychotropic drugs and their effects on physical performance for the purpose of providing empirical information and deriving prescription and therapy recommendations for clinical practice.

METHODS

We systematically searched PubMed, PsycInfo, and Cochrane databases and extracted human studies investigating the effect of psychotropic drugs on parameters associated with the level of physical performance, such as exercise time, oxygen consumption, heart rate, muscle contraction or blood lactate concentration in physically healthy participants. 36 studies - comprising a broad range of psychotropic agents, such as antidepressants, antipsychotics, sedatives, and stimulants - were selected for final analyses.

RESULTS

Most studies (N = 32) were randomized controlled trials (RCT) with a double-blind crossover design. Antidepressants (N = 21) were the most frequently studied drug class, with contradictory results e.g., performance enhancement in warm environment but not in temperate conditions for bupropion or inconsistent findings between studies for other antidepressants. Antipsychotics (N = 3) mainly showed impairing effects on physical performance, while stimulants (N = 4) were often performance-enhancing. Sedatives (N = 9) may cause a hangover effect.

CONCLUSION

The examined studies with heterogeneous design showed different effects of psychiatric medications on physical performance. Antipsychotics seemed to be performance impairing, while the findings for antidepressants and sedatives were more inconsistent. Stimulants were the only group with consistent performance-enhancing effects. However, most studies were conducted with a small sample size (N < 10), mostly in well-trained subjects rather than in patients with psychiatric disorders, and most studies used single-dose designs. These issues impede the formulation of generalized conclusions for treatment regimes and should therefore be considered in further longitudinal studies for clinically reliable statements. Nevertheless, answering our research question is quite relevant for clinical practice and therapeutic prescription and should be further investigated especially considering the high drop-out rates in drug treatment.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=276103], identifier [CRD42021276103].

The Mental Health of Athletes: Recreational to Elite

ABSTRACT

Athletes at all levels of competition are susceptible to mental health symptoms and disorders, and this has been a topic of increased research attention in recent years. The most common such conditions will be highlighted in this article, with a clinical focus on unique aspects of presentation, diagnosis, and management among athletes. Conditions addressed include depression, anxiety and related disorders, eating disorders, sleep concerns, attention-deficit/hyperactivity disorder, bipolar and psychotic disorders, and substance use disorders and behavioral addictions. Athletes experience particular physiologic and psychosocial demands that impact how they present symptomatically and how treatment modalities, including psychotherapy and pharmacologic treatments, impact them.

Mental health in elite athletes: International Olympic Committee consensus statement (2019)

Mental health symptoms and disorders are common among elite athletes, may have sport related manifestations within this population and impair performance. Mental health cannot be separated from physical health, as evidenced by mental health symptoms and disorders increasing the risk of physical injury and delaying subsequent recovery. There are no evidence or consensus based guidelines for diagnosis and management of mental health symptoms and disorders in elite athletes. Diagnosis must differentiate character traits particular to elite athletes from psychosocial maladaptations.

Management strategies should address all contributors to mental health symptoms and consider biopsychosocial factors relevant to athletes to maximise benefit and minimise harm. Management must involve both treatment of affected individual athletes and optimising environments in which all elite athletes train and compete. To advance a more standardised, evidence based approach to mental health symptoms and disorders in elite athletes, an International Olympic Committee Consensus Work Group critically evaluated the current state of science and provided recommendations.

Rats with higher intrinsic exercise capacities exhibit greater preoptic dopamine levels and greater mechanical and thermoregulatory efficiencies while running

The present study investigated whether intrinsic exercise capacity affects the changes in thermoregulation, metabolism and central dopamine (DA) induced by treadmill running. Male Wistar rats were subjected to three incremental exercises and ranked as low-performance (LP), standard-performance (SP), and high-performance (HP) rats. In the first experiment, abdominal (TABD) and tail (TTAIL) temperatures were registered in these rats during submaximal exercise (SE) at 60% of maximal speed. Immediately after SE, rats were decapitated and concentrations of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were determined in the preoptic area (POA). In the second experiment, oxygen consumption was measured and mechanical efficiency (ME) was calculated in these rats during an incremental exercise. HP rats ran for longer periods and were fatigued with higher TABD values, with no difference in TTAIL. Nevertheless, thermoregulatory efficiency was higher in HP rats, compared with other groups. DA and DOPAC concentrations in the POA were increased by SE, with higher levels in HP compared with LP and SP rats. V̇o2 also differed between groups, with HP rats displaying a lower consumption throughout the incremental exercise but a higher V̇o2 at fatigue. ME, in turn, was consistently higher in HP than in LP and SP rats. Thus, our results show that HP rats have greater TABD values at fatigue, which seem to be related to a higher dopaminergic activity in the POA. Moreover, HP rats exhibited a greater thermoregulatory efficiency during exercise, which can be attributed to a lower V̇o2, but not to changes in tail heat loss mechanisms.

NEW & NOTEWORTHY Our findings reveal that rats with higher intrinsic exercise capacities have greater thermoregulatory efficiencies and increased dopaminergic activity in the preoptic area, a key brain area in thermoregulatory control, while exercising. Moreover, higher intrinsic exercise capacities are associated with decreased oxygen consumption for a given exercise intensity, which indicates greater mechanical efficiencies. Collectively, these findings help to advance our knowledge of why some rats of a given strain can exercise for longer periods than others.

Possible Biological Mechanisms Linking Mental Health and Heat-A Contemplative Review

This review provides examples of possible biological mechanisms that could, at least partly, explain the existing epidemiological evidence of heatwave-related exacerbation of mental disease morbidity. The author reviews the complicated central processes involved in the challenge of maintaining a stable body temperature in hot environments, and the maladaptive effects of certain psychiatric medicines on thermoregulation. In addition, the author discusses some alternative mechanisms, such as interrupted functional brain connectivity and the effect of disrupted sleep, which may further increase the vulnerability of mental health patients during heatwaves.

Predicting the ergogenic response to methylphenidate

PURPOSE

Methylphenidate (MPH) and other stimulants have been shown to enhance physical performance. However, stimulant research has almost exclusively been conducted in young, active persons with a normal BMI, and may not generalize to other groups. The purpose of this study was to determine whether the ergogenic response to MPH could be predicted by individual level characteristics.

METHODS

We investigated whether weekly minutes of moderate-to-vigorous physical activity (MVPA), age, and BMI could predict the ergogenic response to MPH. In a double-blind, cross-over design 29 subjects (14M, 15F, 29.7 ± 9.68 years, BMI: 26.1 ± 6.82, MVPA: 568.8 ± 705.6 min) ingested MPH or placebo before performing a handgrip task. Percent change in mean force between placebo and MPH conditions was used to evaluate the extent of the ergogenic response.

RESULTS

Mean force was significantly higher in MPH conditions [6.39% increase, T(25) = 3.09, p = 0.005 118.8 ± 37.96 (± SD) vs. 111.8 ± 34.99 Ns] but variable (coefficient of variation:163%). Using linear regression, we observed that min MVPA (T(25) = -2.15, β = -0.400, p = 0.044) and age [T(25) = -3.29, β = -0.598, p = 0.003] but not BMI [T(25) = 1.67, β = 0.320 p = 0.109] significantly predicted percent change in mean force in MPH conditions.

CONCLUSIONS

We report that lower levels of physical activity and younger age predict an improved ergogenic response to MPH and that this may be explained by differences in dopaminergic function. This study illustrates that the ergogenic response to MPH is partly dependent on individual differences such as habitual levels of physical activity and age.

The sports psychiatrist and psychiatric medication

There are several critical factors to consider in prescribing psychiatric medications to athletes. In addition to the usual considerations when prescribing any psychotropic agent to any patient, the prescriber in this case should pay careful attention to: (1) potential negative impact of the medication on athletic performance, (2) potential performance-enhancing effects, and (3) potential safety risks. This paper describes an updated review of relevant research findings and considerations in the above areas within various categories of psychiatric medications. Many methodological concerns exist with the studies that have examined psychotropic medication use by athletes. These include: small sample sizes; use of the medication in dosing strategies (e.g. single dose) that do not replicate how they are usually taken in the real world; use of primarily male subjects only; use of performance measures (e.g. subtraction, multitask) in some studies that may not align with physical demands experienced by athletes in their natural athletic environments; and not using athletes who actually have the psychiatric disorder or symptom the medication was designed to treat. Despite these concerns, data currently available provide at least some guidance for clinicians wishing to make informed decisions about psychotropic prescribing for their athlete-patients.

Psychiatric medication preferences of sports psychiatrists

OBJECTIVES

When prescribing psychiatric medications to athletes, it is important to consider issues that are especially important for this population, including side effects, safety concerns, and anti-doping policies. Only one report, from 2000, describes the prescribing preferences of psychiatrists who work with athletes. This manuscript aims to update the findings from that report, so as to help inform prescribing practices of primary care physicians, psychiatrists, and other clinicians who work with athletes.

METHODS

Physician members of the International Society for Sports Psychiatry (ISSP) were sent an email invitation in 2016 to complete an anonymous web-based survey on psychiatric medication prescribing preferences in working with athletes with a variety of mental health conditions.

RESULTS

Forty of 100 (40%) members of the ISSP who identified as physicians and who were emailed the survey ultimately completed it. Top choices of psychiatric medications for athletes across categories assessed included: bupropion for depression without anxiety and without bipolar spectrum disorder; escitalopram for generalized anxiety disorder; melatonin for insomnia; atomoxetine for attention-deficit/hyperactivity disorder; lamotrigine for bipolar spectrum disorders; and aripiprazole for psychotic disorders.

CONCLUSION

Prescribers of psychiatric medications for athletes tended to favor medications that are relatively more energizing and less likely to cause sedation, weight gain, cardiac side effects, and tremor. Additionally, prescribing preferences for athletes diverged from many of the prescribing trends seen for patients within the general population, in keeping with the assumption that different factors are considered when prescribing for athletes versus for the general population.

Neurophysiological effects of exercise in the heat

Fatigue during prolonged exercise is a multifactorial phenomenon. The complex interplay between factors originating from both the periphery and the brain will determine the onset of fatigue. In recent years, electrophysiological and imaging tools have been fine-tuned, allowing for an improved understanding of what happens in the brain. In the first part of the review, we present literature that studied the changes in electrocortical activity during and after exercise in normal and high ambient temperature. In general, exercise in a thermo-neutral environment or at light to moderate intensity increases the activity in the β frequency range, while exercising at high intensity or in the heat reduces β activity. In the second part, we review literature that manipulated brain neurotransmission, through either pharmacological or nutritional means, during exercise in the heat. The dominant outcomes were that manipulations changing brain dopamine concentration have the potential to delay fatigue, while the manipulation of serotonin had no effect and noradrenaline reuptake inhibition was detrimental for performance in the heat. Research on the effects of neurotransmitter manipulations on brain activity during or after exercise is scarce. The combination of brain imaging techniques with electrophysiological measures presents one of the major future challenges in exercise physiology/neurophysiology.

Central dopaminergic neurotransmission plays an important role in thermoregulation and performance during endurance exercise

Dopamine (DA) has been widely investigated for its potential role in determining exercise performance. It was originally thought that DA's ergogenic effect was by mediating psychological responses. Recently, some studies have also suggested that DA may regulate physiological responses, such as thermoregulation. Hyperthermia has been demonstrated as an important limiting factor during endurance exercise. DA is prominent in the thermoregulatory centre, and changes in DA concentration have been shown to affect core temperature regulation during exercise. Some studies have proposed that DA or DA/noradrenaline (NA) reuptake inhibitors can improve exercise performance, despite hyperthermia during exercise in the heat. DA/NA reuptake inhibitors also increase catecholamine release in the thermoregulatory centre. Intracerebroventricularly injected DA has been shown to improve exercise performance through inhibiting hyperthermia-induced fatigue, even at normal ambient temperatures. Further, caffeine has been reported to increase DA release in the thermoregulatory centre and improves endurance exercise performance despite increased core body temperature. Taken together, DA has been shown to have ergogenic effects and increase heat storage and hyperthermia tolerance. The mechanisms underlying these effects seem to involve limiting/overriding the inhibitory signals from the central nervous system that result in cessation of exercise due to hyperthermia.

A Catecholamine Precursor Does Not Influence Exercise Performance in Warm Conditions

PURPOSE

Acute doses of Sinemet® (L-DOPA combined with carbidopa) previously failed to influence prolonged exercise performance in a temperate environment, but it is not known whether acute doses of L-DOPA timed to reach maximum plasma concentrations (Cmax) during exercise will improve prolonged cycling performance in warm conditions (30.2°C ± 0.2°C, 50% ± 1%).

METHODS

Ten physically active men (age, 26 ± 4 yr; height, 1.76 ± 0.08 m; body mass, 76.3 ± 10.6 kg; V˙O2peak, 57 ± 8 mL·kg(-1)·min(-1)) were recruited for this study. Participants cycled for 1 h at 60% V˙O2peak followed by a 30-min exercise test, during which they were instructed to complete as much work as possible. Heart rate, skin and core temperatures, as well as RPE and thermal stress were recorded throughout the exercise, and blood samples were collected at rest, at 15-min intervals during the first hour of exercise, and at the end of the exercise test. Finger tapping tests at the beginning and end of the exercise were conducted to examine fine motor control.

RESULTS

There was no significant difference in the work done on the placebo (314 ± 43 kJ) and L-DOPA trials (326 ± 48 kJ, P = 0.276). Prolactin concentrations were increased at the end of the exercise in all trials (P < 0.001), but this response was attenuated at the end of the exercise for the L-DOPA trial (11.4 ± 5.5 ng·mL(-1)) and placebo trials (20.8 ± 3.3 ng·mL(-1), P = 0.003). No differences between trials were found for any other measure.

CONCLUSIONS

The results suggest that increasing central catecholamine availability inhibits the normal prolactin response to exercise in the heat but does not alter performance, thermoregulation, or sympathetic outflow.

Performance in the heat-physiological factors of importance for hyperthermia-induced fatigue

This article presents a historical overview and an up-to-date review of hyperthermia-induced fatigue during exercise in the heat. Exercise in the heat is associated with a thermoregulatory burden which mediates cardiovascular challenges and influence the cerebral function, increase the pulmonary ventilation, and alter muscle metabolism; which all potentially may contribute to fatigue and impair the ability to sustain power output during aerobic exercise. For maximal intensity exercise, the performance impairment is clearly influenced by cardiovascular limitations to simultaneously support thermoregulation and oxygen delivery to the active skeletal muscle. In contrast, during submaximal intensity exercise at a fixed intensity, muscle blood flow and oxygen consumption remain unchanged and the potential influence from cardiovascular stressing and/or high skin temperature is not related to decreased oxygen delivery to the skeletal muscles. Regardless, performance is markedly deteriorated and exercise-induced hyperthermia is associated with central fatigue as indicated by impaired ability to sustain maximal muscle activation during sustained contractions. The central fatigue appears to be influenced by neurotransmitter activity of the dopaminergic system, but inhibitory signals from thermoreceptors arising secondary to the elevated core, muscle and skin temperatures and augmented afferent feedback from the increased ventilation and the cardiovascular stressing (perhaps baroreceptor sensing of blood pressure stability) and metabolic alterations within the skeletal muscles are likely all factors of importance for afferent feedback to mediate hyperthermia-induced fatigue during submaximal intensity exercise. Taking all the potential factors into account, we propose an integrative model that may help understanding the interplay among factors, but also acknowledging that the influence from a given factor depends on the exercise hyperthermia situation.

Cardiovascular stimulant actions of bupropion in comparison to cocaine in the rat

Stimulants are banned in competition by the World Anti-Doping Agency, except for a small number of therapeutic agents subject to monitoring, including bupropion. We have examined the potency of bupropion in comparison with two agents banned in competition, adrafinil and modafinil, and with cocaine and desipramine as blockers of the noradrenaline re-uptake transporter in peripheral tissues of the rat. For studies in vivo, the pressor response to noradrenaline in the anaesthetized rat was studied. Cocaine, desipramine and bupropion at doses of 0.1, 0.3 and 1mg/kg, respectively, significantly increased the pressor response to noradrenaline. Overall, cocaine and desipramine were approximately 2-5 times more potent than bupropion in vivo in the rat. Adrafinil and modafinil (both 3mg/kg) did not significantly affect the pressor response. Bupropion was chosen for further study. In 1Hz paced rat right ventricular strips, bupropion (30μM) significantly increased the potency of noradrenaline at increasing the force of contraction. In rat vas deferens, bupropion and cocaine produced concentration-dependent increases in the contractile response to nerve stimulation, and cocaine was 11 times more potent than bupropion. Since bupropion is used clinically in doses of up to 300mg, it is likely that bupropion has actions at the noradrenaline transporter, and thus cardiovascular stimulant actions, in clinical doses. This may explain findings of increased exercise performance with bupropion.

Neurophysiological determinants of theoretical concepts and mechanisms involved in pacing

Fatigue during prolonged exercise is often described as an acute impairment of exercise performance that leads to an inability to produce or maintain a desired power output. In the past few decades, interest in how athletes experience fatigue during competition has grown enormously. Research has evolved from a dominant focus on peripheral causes of fatigue towards a complex interplay between peripheral and central limitations of performance. Apparently, both feedforward and feedback mechanisms, based on the principle of teleoanticipation, regulate power output (e.g., speed) during a performance. This concept is called 'pacing' and represents the use of energetic resources during exercise, in a way such that all energy stores are used before finishing a race, but not so far from the end of a race that a meaningful slowdown can occur.It is believed that the pacing selected by athletes is largely dependent on the anticipated exercise duration and on the presence of an experientially developed performance template. Most studies investigating pacing during prolonged exercise in ambient temperatures, have observed a fast start, followed by an even pace strategy in the middle of the event with an end sprint in the final minutes of the race. A reduction in pace observed at commencement of the event is often more evident during exercise in hot environmental conditions. Further, reductions in power output and muscle activation occur before critical core temperatures are reached, indicating that subjects can anticipate the exercise intensity and heat stress they will be exposed to, resulting in a tactical adjustment of the power output. Recent research has shown that not only climatic stress but also pharmacological manipulation of the central nervous system has the ability to cause changes in endurance performance. Subjects seem to adapt their strategy specifically in the early phases of an exercise task. In high-ambient temperatures, dopaminergic manipulations clearly improve performance. The distribution of the power output reveals that after dopamine reuptake inhibition, subjects are able to maintain a higher power output compared with placebo. Manipulations of serotonin and, especially, noradrenaline, have the opposite effect and force subjects to decrease power output early in the time trial. Interestingly, after manipulation of brain serotonin, subjects are often unable to perform an end sprint, indicating an absence of a reserve capacity or motivation to increase power output. Taken together, it appears that many factors, such as ambient conditions and manipulation of brain neurotransmitters, have the potential to influence power output during exercise, and might thus be involved as regulatory mechanisms in the complex skill of pacing.

Brain mapping after prolonged cycling and during recovery in the heat

The aim of this study was to determine the effect of prolonged intensive cycling and postexercise recovery in the heat on brain sources of altered brain oscillations. After a max test and familiarization trial, nine trained male subjects (23 ± 3 yr; maximal oxygen uptake = 62.1 ± 5.3 ml·min(-1)·kg(-1)) performed three experimental trials in the heat (30°C; relative humidity 43.7 ± 5.6%). Each trial consisted of two exercise tasks separated by 1 h. The first was a 60-min constant-load trial, followed by a 30-min simulated time trial (TT1). The second comprised a 12-min simulated time trial (TT2). After TT1, active recovery (AR), passive rest (PR), or cold water immersion (CWI) was applied for 15 min. Electroencephalography was measured at baseline and during postexercise recovery. Standardized low-resolution brain electromagnetic tomography was applied to accurately pinpoint and localize altered electrical neuronal activity. After CWI, PR and AR subjects completed TT2 in 761 ± 42, 791 ± 76, and 794 ± 62 s, respectively. A prolonged intensive cycling performance in the heat decreased β activity across the whole brain. Postexercise AR and PR elicited no significant electrocortical differences, whereas CWI induced significantly increased β3 activity in Brodmann areas (BA) 13 (posterior margin of insular cortex) and BA 40 (supramarginal gyrus). Self-paced prolonged exercise in the heat seems to decrease β activity, hence representing decreased arousal. Postexercise CWI increased β3 activity at BA 13 and 40, brain areas involved in somatosensory information processing.

A dopamine/noradrenaline reuptake inhibitor improves performance in the heat, but only at the maximum therapeutic dose

A maximal dose of bupropion has enabled subjects to maintain a higher power output than reported during the placebo session in the heat. Because this drug is taken in different doses it is important to know if there is a dose-response relationship with regard to exercise at high ambient temperature. Ten well-trained male cyclists ingested placebo (pla; 200 mg) or bupropion (50%, 75%, 100% of maximal dose: bup50: 150 mg; bup75: 225 mg; bup100: 300 mg) the evening before and morning of the experimental trial. Trials were conducted in 30 °C (humidity 48%). Subjects cycled for 60 min at 55% W (max) , immediately followed by a time trial to measure performance. Bup100 improved performance (pla: 33'42" ± 2'06"; bup100: 32'06" ± 1'54"; P = 0.035). Bupropion increased core temperature at the end of exercise, while heart rate was higher only in the bup100 trial (P < 0.05). No changes in rating of perceived exertion (RPE) or thermal sensation were found. Lower doses of bupropion were not ergogenic, indicating there was no dose-response effect. Interestingly, despite an increase in core temperature and improved performance in the maximal dose, there was no change in RPE and thermal sensation, suggesting an altered motivation or drive to continue exercise.

The critical limiting temperature and selective brain cooling: neuroprotection during exercise?

There is wide consensus that long duration exercise in the heat is impaired compared with cooler conditions. A common observation when examining exercise tolerance in the heat in laboratory studies is the critical limiting core temperature (CLT) and the apparent attenuation in central nervous system (CNS) drive leading to premature fatigue. Selective brain cooling (SBC) purportedly confers neuroprotection during exercise heat stress by attenuating the increase in brain temperature. As the CLT is dependent on heating to invoke a reduction in efferent drive, it is thus not compatible with SBC which supposedly attenuates the rise in brain temperature. Therefore, the CLT and SBC hypotheses cannot be complimentary if the goal is to confer neuroprotection from thermal insult as it is counter-intuitive to selectively cool the brain if the purpose of rising brain temperature is to down-regulate skeletal muscle recruitment. This presents a circular model for which there is no apparent end to the ultimate physiological outcome; a 'hot brain' selectively cooled in order to reduce the CNS drive to skeletal muscle. This review will examine the postulates of the CLT and SBC with their relationship to the avoidance of a 'hot brain' which together argue for a theoretical position against neuroprotection as the key physiological strategy in exercise-induced hyperthermia.

Effect of five different recovery methods on repeated cycle performance

PURPOSE

The aim of this study was to determine the influence of five different recovery strategies on repeated simulated time trial (TT) performance on a stationary cycle ergometer.

METHODS

Study 1 (n=8, male, club-level trained; V˙O2max: 56.9 ± 3.8 mL·min·kg) investigated the influence of passive rest with or without upper leg cooling (cooling device set at 0 °C or 10 °C) and compression after a first time trial (TT1) on a second time trial (TT2). Study 2 (n=9, male, club-level trained; V˙O2max: 53.3 ± 5.2 mL·min·kg) examined the influence of active recovery (AR) with or without upper leg cooling (cooling device set at 0 °C) applied after TT1 on TT2. Exhaustive exercise consisted of a cycle exercise at 55% Wmax lasting 30 min, immediately followed by a TT in which subjects had to complete a preset amount of work, equal to 30 min at 75% Wmax, as fast as possible. Immediately after TT1, a different recovery intervention was used for 20 min, and then subjects passively rested for 100 min before starting TT2. TT performance and physiological parameters were registered during the experiments.

RESULTS

In both studies, we observed that TT performance did not significantly change for either of the recovery interventions. During the cooling interventions, skin temperatures significantly decreased (P<0.05). AR + cooling + compression versus AR (study 2) clearly showed a significantly (P<0.05) faster decrease of the blood lactate concentration ([BLa]) during the recovery period after TT1 and a lower [BLa] during TT2.

CONCLUSIONS

Twenty minutes after cooling (device set at 0 °C or 10 °C), AR or the combined recovery method had comparable effects as passive recovery on the maintenance of TT2 performance 120 min after the first TT (TT1). After AR, however, subjects seemed to perform slightly better during TT2.

Is it time to retire the A.V. Hill Model?: A rebuttal to the article by Professor Roy Shephard

Recent publications by Emeritus Professor Roy Shephard propose that a "small group of investigators who have argued repeatedly (over the past 13 years) for a 'Central Governor'," should now either "Put up or shut up." Failing this, their 'hypothesis' should be 'consigned to the bottom draw for future reference'; but Professor Shephard's arguments are contradictory. Thus, in different sections of his article, Professor Shephard explains: why there is no need for a brain to regulate exercise performance; why there is no proof that the brain regulates exercise performance; and why the brain's proven role in the regulation of exercise performance is already so well established that additional comment and research is unnecessary. Hence, "The higher centres of an endurance athlete … call forth an initial effort … at a level where a minimal accumulation of lactate in the peripheral muscles is sensed." Furthermore, "a variety of standard texts have illustrated the many mutually redundant feedback loops (to the nervous system) that limit exercise." Yet, the figure from Professor Shephard's 1982 textbook does not contain any links between the nervous system, "many mutually redundant feedback loops" and skeletal muscle. This disproves his contradictory claims that although there is neither any need for, nor any proof of, any role of the brain in the regulation of exercise performance, the physiological mechanisms for this (non-existent) control were already well established in 1982. In contrast, the Central Governor Model (CGM) developed by our "small group … in a single laboratory" after 1998, provides a simple and unique explanation of how 'redundant feedback loops' can assist in the regulation of exercise behaviour. In this rebuttal to his article, I identify (i) the numerous contradictions included in Professor Shephard's argument; (ii) the real meaning of the facts that he presents; (iii) the importance of the evidence that he ignores; and (iv) the different philosophies of how science should be conducted according to either the Kuhnian or the Popperian philosophies of scientific discovery. My conclusion is that the dominance of an authoritarian Kuhnian philosophy, which refuses to admit genuine error or "the need to alter one's course of belief or action," explains why there is little appetite in the exercise sciences for the acceptance of genuinely novel ideas such as the CGM. Furthermore, to advance the case for the CGM, I now include evidence from more than 30 studies, which, in my opinion, can only be interpreted according to a model of exercise regulation where the CNS, acting in an anticipatory manner, regulates the exercise behaviour by altering skeletal muscle recruitment, specifically to ensure that homeostasis is maintained during exercise. Since few, if any, of those studies can be explained by the 'brainless' A.V. Hill Cardiovascular Model on which Professor Shephard bases his arguments, I argue that it is now the appropriate time to retire that model. Perhaps this will bring to an end the charade that holds either (i) that the brain plays no part in the regulation of exercise performance; or, conversely, (ii) that the role of the brain is already so well defined that further research by other scientists is unnecessary. However, this cannot occur in a discipline that is dominated by an authoritarian Kuhnian philosophy.

Central fatigue and neurotransmitters, can thermoregulation be manipulated?

Fatigue is a complex phenomenon that can be evoked by peripheral and central factors. Although it is obvious that fatigue has peripheral causes such as glycogen depletion and cardiovascular strain, recent literature also focuses on the central origin of fatigue. It is clear that different brain neurotransmitters--such as serotonin, dopamine and noradrenaline--are implicated in the occurrence of fatigue, but manipulation of these neurotransmitters produced no conclusive results on performance in normal ambient temperature. Exercise in the heat not only adds an extra challenge to the cardiorespiratory system, but also to the brain. This provides a useful tool to investigate the association between exercise-induced hyperthermia and central fatigue. This review focuses on the effects of pharmacological manipulations on performance and thermoregulation in different ambient temperatures. Dopaminergic reuptake inhibition appears to counteract hyperthermia-induced fatigue in 30 °C, while noradrenergic neurotransmission shows negative effects on performance in both normal and high temperature, and serotonergic manipulations did not lead to significant changes in performance. It is, however, unlikely that one neurotransmitter system is responsible for the delay or onset of fatigue. Further research is required to determine the exact mechanisms of fatigue in different environmental conditions.

Sport psychiatry: a systematic review of diagnosis and medical treatment of mental illness in athletes

Sport psychiatry focuses on diagnosis and treatment of psychiatric illness in athletes in addition to utilization of psychological approaches to enhance performance. As this field and its research base are relatively new, clinicians often deliver psychiatric care to athletes without a full understanding of the diagnostic and therapeutic issues unique to this population. In this systematic review, we discuss published findings relating to psychiatric diagnosis and medical treatment of mental illness in athletes. There have been several studies looking at the prevalence of some psychiatric disorders in various athlete populations. Eating disorders and substance abuse are the most studied of these disorders and appear to be common problems in athletes. However, to provide informed understanding and treatment, we especially need more research on overtraining syndrome, bipolar disorder, suicidality, anxiety disorders, attention-deficit hyperactivity disorder (ADHD) and psychosis in athletes. Research is needed in the areas of prevalence, risk factors, prognosis and the unique experiences facing athletes with any of these disorders. Additionally, there have not been any large, systematic studies on the use of psychotropic medications in athletes. Small studies suggest that some medications may either be performance enhancing or detrimental to performance, but we need larger studies with rigorous methodology. Higher level athletes suffering from psychiatric symptoms often have reservations about taking medications with unknown performance and safety effects, and methodological issues with the current literature database preclude any definitive conclusions on performance effects of psychiatric medications. We need many more, higher quality studies on the use by athletes of antidepressants, mood stabilizers, anxiolytics, stimulants and other ADHD medications, sedative-hypnotics and antipsychotics. Such studies should utilize sensitive performance measures and involve longer term use of psychotropic medications. Furthermore, study subjects should include athletes who actually have the psychiatric disorder for which the medication is proposed, and should include more women.

Time to move beyond a brainless exercise physiology: the evidence for complex regulation of human exercise performance

In 1923, Nobel Laureate A.V. Hill proposed that maximal exercise performance is limited by the development of anaerobiosis in the exercising skeletal muscles. Variants of this theory have dominated teaching in the exercise sciences ever since, but 90 years later there is little biological evidence to support Hill’s belief, and much that disproves it. The cardinal weakness of the Hill model is that it allows no role for the brain in the regulation of exercise performance. As a result, it is unable to explain at least 6 common phenomena, including (i) differential pacing strategies for different exercise durations; (ii) the end spurt; (iii) the presence of fatigue even though homeostasis is maintained; (iv) fewer than 100% of the muscle fibers have been recruited in the exercising limbs; (v) the evidence that a range of interventions that act exclusively on the brain can modify exercise performance; and (vi) the finding that the rating of perceived exertion is a function of the relative exercise duration rather than the exercise intensity. Here I argue that the central governor model (CGM) is better able to explain these phenomena. In the CGM, exercise is seen as a behaviour that is regulated by complex systems in the central nervous system specifically to ensure that exercise terminates before there is a catastrophic biological failure. The complexity of this regulation cannot be appreciated if the body is studied as a collection of disconnected components, as is the usual approach in the modern exercise sciences.

Alterations in central fatigue by pharmacological manipulations of neurotransmitters in normal and high ambient temperature

The scientific evidence is reviewed for the involvement of the brain monoamines serotonin, dopamine and noradrenaline (norepinephrine) in the onset of fatigue, in both normal and high ambient temperatures. The main focus is the pharmacological manipulations used to explore the central fatigue hypothesis. The original central fatigue hypothesis emphasizes that an exercise-induced increase in serotonin is responsible for the development of fatigue. However, several pharmacological studies attempted and failed to alter exercise capacity through changes in serotonergic neurotransmission in humans, indicating that the role of serotonin is often overrated. Recent studies, investigating the inhibition of the reuptake of both dopamine and noradrenaline, were capable of detecting changes in performance, specifically when ambient temperature was high. Dopamine and noradrenaline are prominent in innervated areas of the hypothalamus, therefore changes in the catecholaminergic concentrations may also be expected to be involved with the regulation of body core temperature during exercise in the heat. Evidence from different studies suggests that it is very unlikely that one neurotransmitter system is responsible for the appearance of central fatigue. The exact mechanism of fatigue is not known; presumably a complex interplay between both peripheral and central factors induces fatigue. Central fatigue will be determined by the collaboration of the different neurotransmitter systems, with the most important role possibly being for the catecholamines dopamine and noradrenaline.

Time trial performance in normal and high ambient temperature: is there a role for 5-HT?

The original central fatigue hypothesis suggested that fatigue during prolonged exercise might be due to higher 5-HT activity. Therefore, we examined the effects of acute administration of a selective 5-HT reuptake inhibitor (SSRI) on performance and thermoregulation. Eleven healthy trained male cyclists completed four experimental trials (two in 18 degrees C, two in 30 degrees C) in a double-blind randomised crossover design. Subjects ingested either a placebo (PLA: lactose 2 x 10 mg) or citalopram (CITAL 2 x 10 mg) on the evening before and the morning of the trial. Subjects cycled for 60 min at 55% W(max), immediately followed by a time trial (TT) to measure performance. The significance level was set at P < 0.05. Acute SSRI did not significantly change performance on the TT (18 degrees C P = 0.518; 30 degrees C P = 0.112). During recovery at 30 degrees C, core temperature was significantly lower in the CITAL trial (P < 0.012). At 30 degrees C heart rate was significantly lower after exercise in CITAL (P = 0.013). CITAL significantly increased cortisol concentrations at rest (P = 0.016), after the TT (P = 0.006) and after 15-min recovery (P = 0.041) at 30 degrees C. 5-HT reuptake inhibition did not cause significant reductions in performance. Core temperature was significantly lower only after the time trial in heat after CITAL administration. The present work failed to prove whether or not 5-HT has an exclusive role in the onset of centrally mediated fatigue during prolonged exercise in both normal and high ambient temperature.