Exercise thermoregulation and hyperprolactinaemia

Influence of Exogenous Factors Related to Nutritional and Hydration Strategies and Environmental Conditions on Fatigue in Endurance Sports: A Systematic Review with Meta-Analysis

The aim of this systematic review with meta-analysis was to examine the influence of exogenous factors related to nutritional and hydration strategies and environmental conditions, as modulators of fatigue, including factors associated with performance fatigability and perceived fatigability, in endurance tests lasting 45 min to 3 h. A search was carried out using four databases: PubMed, Web of Science, SPORTDiscus, and EBSCO. A total of 5103 articles were screened, with 34 included in the meta-analysis. The review was registered with PROSPERO (CRD42022327203) and adhered to the PRISMA guidelines. The study quality was evaluated according to the PEDro score and assessed using Rosenthal's fail-safe N. Carbohydrate (CHO) intake increased the time to exhaustion (p < 0.001) and decreased the heart rate (HR) during the test (p = 0.018). Carbohydrate with protein intake (CHO + PROT) increased lactate during the test (p = 0.039). With respect to hydration, dehydrated individuals showed a higher rate of perceived exertion (RPE) (p = 0.016) and had a higher body mass loss (p = 0.018). In hot conditions, athletes showed significant increases in RPE (p < 0.001), HR (p < 0.001), and skin temperature (p = 0.002), and a decrease in the temperature gradient (p < 0.001) after the test. No differences were found when athletes were subjected to altitude or cold conditions. In conclusion, the results revealed that exogenous factors, such as nutritional and hydration strategies, as well as environmental conditions, affected fatigue in endurance sports, including factors associated with performance fatigability and perceived fatigability.

Potential Biomarkers of Peripheral and Central Fatigue in High-Intensity Trained Athletes at High-Temperature: A Pilot Study with Momordica charantia (Bitter Melon)

Among potent dietary supplements, Momordica charantia, commonly called bitter melon, has various biological effects, such as antioxidant and anti-inflammatory effects, and improves energy metabolism and fatigue recovery. However, it is unknown whether Momordica charantia extract (MCE) induces antifatigue effects during exercise training in high-temperature environments. This study aimed at investigating the efficacy of MCE by examining 10 male tennis players consuming 100 mL MCE/dose (6 times a day over 4 weeks) during the summer training season. Peripheral (ammonia and uric acid) and central (serotonin, dopamine, and prolactin) fatigue parameters were measured before and after MCE consumption; before, during, and after exercise; and the next morning. After consuming MCE supplements, ammonia levels were higher during and after exercise and recovered the next morning, whereas uric acid levels did not change at any time point. Serotonin levels were lower during exercise. Dopamine levels were higher, especially during exercise. Prolactin levels were lower at all time points, especially during and after exercise. Although high-intensity training in a hot environment causes accumulation of fatigue-related metabolites, our results indicate that 4 weeks of MCE intake positively influenced fatigue parameters, suggesting that MCE can efficiently combat fatigue.

Ingestion of caffeine links dopamine and 5-hydroxytryptamine release during half immersion in 42°C hot water in a humans

The aim of this study was to investigate the serum serotonin, prolactin, and plasma dopamine levels in humans with and without caffeine ingestion during and after passive heat loading (half immersion in 42°C hot water). Thirty male volunteers participated in the randomized experiment (control group, n=15 vs. caffeine ingestion group, n=15, 3 mg/kg). After 60 min, passive heat loading was conducted for 30 min. Blood samples were collected and assessed for serum serotonin, dopamine and prolactin with and without caffeine during and after passive heat loading. Serum serotonin was significantly lower in the caffeine ingestion group compared to the control group after passive heat loading for 30 min (Post) (P<0.05) and also after 60 min of resting (P<0.01). Dopamine and prolactin were significantly higher in the caffeine ingestion group than in the control group at the Post time point (P<0.001). In conclusion, 3-mg/kg caffeine ingestion prior to passive heat loading can alter central serotonergic and dopaminergic activity, which may contribute to reduced central fatigue and subsequently, to reduced general fatigue. Prolactin responses during passive heat loading were also significantly related to caffeine ingestion in this study. However, the inhibitory effects of dopamine on prolactin by caffeine remain to be elucidated.

Three different motor task strategies to assess neuromuscular adjustments during fatiguing muscle contractions in young and older men

Healthy aging is associated with a marked decline in motor performance. The functional consequences of applying varying novel or unexpected motor stimuli during intermittent isometric prolonged (fatiguing) motor tasks for lower limb neuromuscular fatigability and steadiness, perception of effort, and blood markers of stress in healthy aged men compared with young men have not been investigated. The participants in this study were 15 young men (aged 22 ± 4 years) and 10 older men (aged 67 ± 6 years). They performed 100 intermittent isometric knee extensions under three experimental conditions involving intermittent isometric contraction tasks according to constant, predictable, and unpredictable torque target sequences. The variability in maximal voluntary contraction averaged 50%, and was 25, 50, and 75% for the three strategies. All included a 5-s contraction and 20-s rest. The main variables were measured before exercise, after 100 repetitions, and 1 h after exercise. In all experimental trials, the decreases in the maximal voluntary contraction and central activation ratio, and the increases in effort sensation and muscle temperature, were smaller in older men than in younger men. The coefficient of variation during the motor performance did not differ between age groups. However, in all three strategies, the dopamine concentration was significantly higher in older than in younger men. The prolactin concentration did not differ significantly between age groups or conditions, although its decrease during loading correlated negatively with the central activation ratio.

Effect of constant, predictable, and unpredictable motor tasks on motor performance and blood markers of stress

An unfamiliar or novel physical stimulus induces activation of dopaminergic neurons within the brain and greater activity in areas involved in emotion; considering this, we aimed to establish whether unpredictable prolonged (fatiguing) motor task (vs. constant vs. predictable) evokes greater dopaminergic activity, enhances neuromuscular performance, motor accuracy, and perception of effort, and delays overall central fatigue. Fifteen healthy male volunteers (aged 22 ± 4 years) were required to perform 1 of 3 exercise trials (at least 1 week apart) of 100 intermittent isometric contraction (IIC) tasks involving knee extensions at 60° flexion. Trials were structured differently by simulated contraction intensity. A fatigue task involved 5-s contractions and 20-s rest. Variables measured before, during, and after IIC were electrically induced force, maximal voluntary contraction, central activation ratio, intramuscular temperature, and blood levels of dopamine, cortisol, and prolactin, and intraindividual motor variability and accuracy (constant and absolute error). We found that IIC increased central and peripheral fatigue, force sensation, and T _mu, and decreased absolute and constant error without visual feedback, but did not affect motor variability. There were no significant differences between the three IIC tasks. However, only unpredictable tasks increased dopaminergic activity, which was insufficient to affect central motivation to perform isometric exercise and alter centrally mediated components of fatigue.

Influence of circulating cytokines on prolactin during slow vs. fast exertional heat stress followed by active or passive recovery

Prolactin (PRL) has been suggested as an indicator of fatigue during exertional heat stress (EHS), given its strong relationship with body core temperature (T(c)); however, the strength of this relationship during different rates of T(c) increase and subsequent recovery is unknown. In addition, given the influence that systemic cytokines, such as interleukin (IL)-6 and tumor necrosis factor (TNF)-α, have on the pituitary gland, it would be of interest to determine the relationship between PRL, IL-6, and TNF-α during EHS. The purpose was to examine the PRL, IL-6, and TNF-α heat stress responses during slow and fast heating and subsequent resting or cold water immersion recovery. On 4 days, nine individuals walked at ≈ 45% (slow heating) or ran at ≈ 65% (fast heating) maximal oxygen consumption on a treadmill in the heat (40°C, 30% relative humidity) until rectal temperature (T(re)) reached 39.5°C (esophageal temperature; fast = 39.41 ± 0.04°C, slow = 39.82 ± 0.09°C). Post-EHS, subjects were either immersed in 2°C water or rested seated until T(re) returned to 38.0°C. Venous blood, analyzed for PRL, IL-6, and TNF-α, was obtained at rest, during exercise (T(re) 38.0, 39.0, 39.5°C), the start of recovery (≈ 5 min after 39.5°C), and subsequent recovery (T(re) 39.0, 38.0°C). IL-6 exhibited myokine properties, given the greater increases with slow heating and lack of increase in TNF-α. A strong temperature-dependent PRL response during slow and fast heating provides additional support for the use of PRL as a peripheral marker of impending fatigue, which is independent of IL-6 and TNF-α cytokine responses.

Peripheral markers of central fatigue in trained and untrained during uncompensable heat stress

The development of fatigue is more pronounced in the heat than thermoneutral environments; however, it is unclear whether biomarkers of central fatigue are consistent with the higher core temperature (T (c)) tolerated by endurance trained (TR) versus untrained (UT) during exertional heat stress (EHS). The purpose of this study was to examine the indicators of central fatigue during EHS in TR versus UT. Twelve TR and 11 UT males (mean ± SE [Formula: see text] = 70 ± 2 and 50 ± 1 mL kg LBM(-1) min(-1), respectively) walked on a treadmill to exhaustion (EXH) in 40°C (dry) wearing protective clothing. Venous blood was obtained at PRE and 0.5°C T (c) increments from 38 to 40°C/EXH. Free tryptophan (f-TRP) decreased dramatically at 39.5°C for the TR. Branch chain amino acids decreased with T (c) and were greater for UT than TR at EXH. Tyrosine and phenylalanine remained unchanged. Serum S100β was undetectable (<5 pg mL(-1)). Albumin was greater for the UT from PRE to 39.0°C and at EXH. Prolactin (PRL) responded to relative thermal strain with similar EXH values despite higher T (c) tolerated for TR (39.7 ± 0.09°C) than UT (39.0 ± 0.09°C). The high EXH PRL values for both groups support its use as a biomarker of the serotonin and dopamine interplay within the brain during the development of central fatigue.

Sexual dysfunction in first-episode schizophrenia patients: results from European First Episode Schizophrenia Trial

Sexual dysfunctions (SDs) occur frequently in schizophrenia patients and have a huge impact on quality of life and compliance. They are often associated with antipsychotic medication. Nicotine consumption, negative or depressive symptoms, and physical illness are also discussed as contributing factors. Data on SD in first-episode schizophrenia patients are scarce.As part of the European First Episode Schizophrenia Trial, first-episode schizophrenia patients were randomly assigned to 5 medication groups. We assessed SD by analyzing selected items from the Udvalg for Kliniske Undersugelser at baseline and at 5 following visits.Differences between antipsychotics were small for all SDs, and fairly little change in the prevalence of SDs was seen over the course of the study. A significantly larger increase of amenorrhea and galactorrhea was seen with amisulpride than with the other medications. In men, higher age, more pronounced Positive and Negative Syndrome Scale general psychopathology symptoms, and higher plasma prolactin levels predicted higher rates of erectile and ejaculatory dysfunctions. Positive and Negative Syndrome Scale negative symptoms and higher age were predictors for decreased libido.In women, higher prolactin plasma levels were identified as a predictor of amenorrhea. Positive and Negative Syndrome Scale negative symptoms predicted decreased libido.All evidence taken together underscores the influence of the disease schizophrenia itself on sexual functioning. In addition, there is a strong correlation between the prolactin-increasing properties of amisulpride and menstrual irregularities.

Circulating androgens in women: exercise-induced changes

Physical exercise is known to strongly stimulate the endocrine system in both sexes. Among these hormones, androgens (e.g. testosterone, androstenedione, dehydroepiandrosterone) play key roles in the reproductive system, muscle growth and the prevention of bone loss. In female athletes, excessive physical exercise may lead to disorders, including delay in the onset of puberty, amenorrhoea and premature osteoporosis. The free and total fractions of circulating androgens vary in response to acute and chronic exercise/training (depending on the type), but the physiological role of these changes is not completely understood. Although it is commonly accepted that only the free fraction of steroids has a biological action, this hypothesis has recently been challenged. Indeed, a change in the total fraction of androgen concentration may have a significant impact on cells (inducing genomic or non-genomic signalling). The purpose of this review, therefore, is to visit the exercise-induced changes in androgen concentrations and emphasize their potential effects on female physiology. Despite some discrepancies in the published studies (generally due to differences in the types and intensities of the exercises studied, in the hormonal status of the group of women investigated and in the methods for androgen determination), exercise is globally able to induce an increase in circulating androgens. This can be observed after both resistance and endurance acute exercises. For chronic exercise/training, the picture is definitely less clear and there are even circumstances where exercise leads to a decrease of circulating androgens. We suggest that those changes have significant impact on female physiology and physical performance.

Effects of short-term prednisolone intake during submaximal exercise

PURPOSE

To examine the prednisolone's ergogenic and metabolic effects during submaximal exercise.

METHODS

Ten recreational male athletes completed two cycling trials at 70-75% peak O2 consumption until exhaustion after either placebo (Pla, lactose) or oral prednisolone (Pred, 60 mg.d(-1) for 1 wk) treatment, according to a double-blind and randomized protocol. Blood samples were collected at rest and during exercise and recovery to determine ACTH, growth hormone (GH), prolactin (PRL), DHEA, insulin, blood glucose, and blood lactate values.

RESULTS

Time of cycling was significantly increased after chronic Pred treatment (Pred: 74.5+/-9.5 min; Pla: 46.1+/-3.3 min, P<0.01). Pred intake significantly lowered basal, exercise, and recovery ACTH, DHEA, and PRL concentrations, whereas GH concentrations were significantly lowered by Pred after 30 min of exercise. Blood glucose and insulin were significantly (P<0.05) increased by Pred during the whole experiment and until 30 min of exercise. Blood lactate concentrations were higher after Pred versus Pla at 10 min of exercise until 10 min of recovery (P<0.05).

CONCLUSION

From these data, short-term Pred intake did seem to significantly improve performance during submaximal exercise, with concomitant alterations in hormonal and metabolic responses. Further studies will be necessary to elucidate the mechanisms of these hormonal and metabolic changes, and to determine whether the changes may be associated with the marked performance improvement obtained.

Possible use of repeated cold stress for reducing fatigue in chronic fatigue syndrome: a hypothesis

BACKGROUND

Physiological fatigue can be defined as a reduction in the force output and/or energy-generating capacity of skeletal muscle after exertion, which may manifest itself as an inability to continue exercise or usual activities at the same intensity. A typical example of a fatigue-related disorder is chronic fatigue syndrome (CFS), a disabling condition of unknown etiology and with uncertain therapeutic options. Recent advances in elucidating pathophysiology of this disorder revealed hypofunction of the hypothalamic-pituitary-adrenal axis and that fatigue in CFS patients appears to be associated with reduced motor neurotransmission in the central nervous system (CNS) and to a smaller extent with increased fatigability of skeletal muscle. There is also some limited evidence that CFS patients may have excessive serotonergic activity in the brain and low opioid tone.

PRESENTATION OF THE HYPOTHESIS

This work hypothesizes that repeated cold stress may reduce fatigue in CFS because brief exposure to cold may transiently reverse some physiological changes associated with this illness. For example, exposure to cold can activate components of the reticular activating system such as raphe nuclei and locus ceruleus, which can result in activation of behavior and increased capacity of the CNS to recruit motoneurons. Cold stress has also been shown to reduce the level of serotonin in most regions of the brain (except brainstem), which would be consistent with reduced fatigue according to animal models of exercise-related fatigue. Finally, exposure to cold increases metabolic rate and transiently activates the hypothalamic-pituitary-adrenal axis as evidenced by a temporary increase in the plasma levels of adrenocorticotropic hormone, beta-endorphin and a modest increase in cortisol. The increased opioid tone and high metabolic rate could diminish fatigue by reducing muscle pain and accelerating recovery of fatigued muscle, respectively.

TESTING THE HYPOTHESIS

To test the hypothesis, a treatment is proposed that consists of adapted cold showers (20 degrees Celsius, 3 minutes, preceded by a 5-minute gradual adaptation to make the procedure more comfortable) used twice daily.

IMPLICATIONS OF THE HYPOTHESIS

If testing supports the proposed hypothesis, this could advance our understanding of the mechanisms of fatigue in CFS.

Thermography and thermoregulation of the face

BACKGROUND

Although clinical diagnosis of thermoregulation is gaining in importance there is no consistent evidence on the value of thermography of the facial region. In particular there are no reference values established with standardised methods.

METHODS

Skin temperatures were measured in the facial area at 32 fixed measuring sites in 26 health subjects (7-72 years) with the aid of a contact thermograph (Eidatherm). A total of 6 measurements were performed separately for the two sides of the face at intervals of equal lengths (4 hours) over a period of 24 hours. Thermoregulation was triggered by application of a cold stimulus in the region of the ipsilateral ear lobe.

RESULTS

Comparison of the sides revealed significant asymmetry of face temperature. The left side of the face showed a temperature that was on the average 0.1 degrees C lower than on the right. No increase in temperature was found following application of the cold stimulus. However, a significant circadian rhythm with mean temperature differences of 0.7 degrees C was observed.

CONCLUSION

The results obtained should be seen as an initial basis for compiling an exact thermoprofile of the surface temperature of the facial region that takes into account the circadian rhythm, thus closing gaps in studies on physiological changes in the temperature of the skin of the face.

Thermoregulation in elite athletes

PURPOSE OF REVIEW

Exercise causes body temperature to rise and the resulting heat stored becomes a factor limiting exercise performance in hot conditions. Loss of heat by evaporative processes leads to hypohydration which itself can eventually impair performance. This review focuses on thermoregulatory and behavioural processes during sustained exercise in the heat.

RECENT FINDINGS

Several studies have implicated cerebral mechanisms in eschewing fatigue due to heat stress. Acclimatization improves performance by affecting heat loss mechanisms, implicating peripheral and central processes. Pharmacological methods of increasing heat tolerance are unacceptable strategies for the athlete, but appropriate precooling measures are effective.

SUMMARY

This review highlights the combination of physiological processes that converge in heat stress during extended exercise. Pharmacological ergogenic aids are discouraged due to likely side effects in cerebral function whereas behavioural measures, including precooling the body, have practical support.