Inter-relationships between pituitary-adrenal hormones and catecholamines during a 6-day Nordic ski race

Overtraining Syndrome as a Complex Systems Phenomenon

The phenomenon of reduced athletic performance following sustained, intense training (Overtraining Syndrome, and OTS) was first recognized more than 90 years ago. Although hundreds of scientific publications have focused on OTS, a definitive diagnosis, reliable biomarkers, and effective treatments remain unknown. The present review considers existing models of OTS, acknowledges the individualized and sport-specific nature of signs/symptoms, describes potential interacting predisposing factors, and proposes that OTS will be most effectively characterized and evaluated via the underlying complex biological systems. Complex systems in nature are not aptly characterized or successfully analyzed using the classic scientific method (i.e., simplifying complex problems into single variables in a search for cause-and-effect) because they result from myriad (often non-linear) concomitant interactions of multiple determinants. Thus, this review 1) proposes that OTS be viewed from the perspectives of complex systems and network physiology, 2) advocates for and recommends that techniques such as trans-omic analyses and machine learning be widely employed, and 3) proposes evidence-based areas for future OTS investigations, including concomitant multi-domain analyses incorporating brain neural networks, dysfunction of hypothalamic-pituitary-adrenal responses to training stress, the intestinal microbiota, immune factors, and low energy availability. Such an inclusive and modern approach will measurably help in prevention and management of OTS.

The impact of sleep restriction while performing simulated physical firefighting work on cortisol and heart rate responses

PURPOSE

Physical work and sleep restriction are two stressors faced by firefighters, yet the combined impact these demands have on firefighters' acute stress responses is poorly understood. The purpose of the present study was to assess the effect firefighting work and sleep restriction have on firefighters' acute cortisol and heart rate (HR) responses during a simulated 3-day and 2-night fire-ground deployment.

METHODS

Firefighters completed multiple days of simulated physical work separated by either an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17). Salivary cortisol was sampled every 2 h, and HR was measured continuously each day.

RESULTS

On day 2 and day 3 of the deployment, the sleep restriction condition exhibited a significantly higher daily area under the curve cortisol level and an elevated cortisol profile in the afternoon and evening when compared with the control condition. Firefighters' HR decreased across the simulation, but there were no significant differences found between conditions.

CONCLUSION

Findings highlight the protective role an 8-h sleep opportunity between shifts of firefighting work has on preserving normal cortisol levels when compared to a 4-h sleep opportunity which resulted in elevated afternoon and evening cortisol. Given the adverse health outcomes associated with chronically high cortisol, especially later in the day, future research should examine how prolonged exposure to firefighting work (including restricted sleep) affects firefighters' cortisol levels long term. Furthermore, monitoring cortisol levels post-deployment will determine the minimum recovery time firefighters need to safely return to the fire-ground.

Effect of equilibrated hydration changes on total body water estimates by bioelectrical impedance analysis

The present study was performed to determine how equilibrated fluctuations in hydration affected the validity of bioelectrical impedance analysis (BIA) for body composition assessment. Total body water (TBW) expansion was induced by a 4 d endurance trial and the subsequent water loss was obtained over the recovery period. Twelve healthy men exercised on a cycle and treadmill alternately for 5 h/d over 4 d at moderate intensity. TBW, fat mass (FM) and fat-free mass (FFM) were assessed 3 d before the trial (control), and on the first and eighth day of recovery (R1 and R8 respectively). TBW was evaluated by 2H dilution (TBW2H) as a reference method and by BIA (TBWBIA) at 100 kHz at the same time. TBW2H increased significantly between the control day and R1 by 1·87 (sd 1·11) litres (P=0·005) and TBWBIA by 1·38 (sd 1·56) litres (P=0·009). Both values returned to the control level on R8. For each period, TBW2H and TBWBIA did not differ significantly and were correlated (r2 0·85, P=0·0004 for the control day; r2 0·63, P=0·03 for R1; r2 0·75, P=0·02 for R8). Plasma Na concentration and osmolality did not differ between the control day, R1 and R8. FFM gain (1208 (sd 1983) g) and FM loss (−1168 (sd 906) g) between the control day and R1 were followed by a FFM decrease (−624 (sd 1281) g) and a FM increase (860 (sd 1212) g) between R1 and R8. As expected, these FFM and FM changes were significantly correlated with TBW variations. The present results provide evidence that BIA may be a useful method for estimating TBW when fluid shifts are equilibrated and electrolyte concentrations are unchanged. However, it is not a valid technique for assessing FM and FFM under these conditions.

Concentrations of cortisol, testosterone and glycosylated haemoglobin (HbA1c) among construction workers with 12-h workdays and extended workweeks

OBJECTIVES

Working on large scale construction sites have been shown to have severe health consequences in terms of increased risk of hospitalization and disability retirement compared to construction work in general. The aim of the present study was to investigate whether large scale construction work involving 12-h workdays and extended workweeks leads to insufficient recovery measured as increased catabolic and decreased anabolic metabolism.

METHODS

The study group comprised 40 male construction workers of which 21 had 12-h workdays and extended workweeks (56 h/workweek). The comparison group consisted of 19 male construction workers, who worked regular hours (37 h/week, weekends off). Measurements of concentrations of cortisol in saliva and free testosterone and glycosylated haemoglobin (HbA(1c)) in blood were made in a repeated measures design during 2 workweeks for both groups supplemented with 1 week off for construction workers with extended workweeks.

RESULTS

The diurnal profile of concentrations of salivary cortisol for construction workers with extended workweeks differed from the diurnal profile of salivary cortisol for those with regular work schedules (P < 0.001). The construction workers with extended workweeks tended to have 15% [95% CI -3%; 37%] higher concentrations of free testosterone in serum compared to construction workers with regular work schedules (P = 0.09). There were no differences between the two groups with respect to concentrations of HbA(1c). There was no increasing trend in concentrations of cortisol or decreasing trend in concentrations of testosterone during the extended workweek. The diurnal profile for concentrations of cortisol differed between workdays and days off for construction workers with extended workweeks (P = 0.003).

CONCLUSION

In conclusion, we observed no indications of insufficient recovery in terms of increased catabolic or decreased anabolic metabolism in construction workers with 12-h workdays and extended workweeks compared to construction workers with regular work schedules.

Heart rate running speed relationships-during exhaustive bouts in the laboratory

The present study was designed to investigate the heart rate-running speed (HR-RS) relationship while exercising continuously, at high intensities, on a treadmill. The purpose was to precisely measure the magnitude of drop in RS necessary to maintain HR during intense exhaustive exercises, and to determine whether the magnitude of drop in RS is directly dependent on exercise intensity. Sixteen male endurance athletes performed five treadmill tests: an incremental test for maximal O2 uptake and maximum aerobic velocity (VMA), and four exhaustive tests: at 82, 86, 89, and 92 % VMA. After an adaptation period of 3 min, the objective was to stabilise HR by adjusting the treadmill speed continuously by +/- 0.5 km x h(-1) every 30 sec. Attained intensities were: 82 % (+/-6), 84 % +/- (6), 89 % (+/-3), and 90 % (+/-6) VMA, respectively [L1, L2] vs. [L3, L4], p < 0.05. Time to exhaustion across the increasing intensities, respectively, were: 36.58 (+/-4.45), 24.63 (+/-3.25), 15.80 (+/-2.00), and 9.87 (+/-1.15) min, p < 0.05, with the exception of L3 vs. L4. The RS/HR ratio vs. speed showed three phases: an increasing adaptive (AB) phase 0-165 sec with an averaging maximal level of 1.67 m x beat(-1) at 165 sec, a transitional period 170-245 sec, and a decreasing (BC) phase 250-1800 sec with a lower level of 1.29 m .beat(-1) at 1800 sec. In our experimental conditions, for high intensities 82 to 90 % VMA, cardiac drift which disturbed the RS-HR relationship with duration was evaluated: -0.143 km x h(-1) per minute for HR stabilisation. This cardiac drift is a linear function of time. Results suggest that HR and RS are not interchangeable variables for this kind of exercises, and it seems more reliable to gauge exercise intensity using RS than HR.

Post-awakening cortisol secretion during basic military training

Salivary free cortisol concentrations in the first 30 min after awakening were assessed in 12 healthy army recruits at the beginning, middle and end of an 11-week intensive physical training course. To ensure strict adherence to protocol saliva collection was supervised and collected on each sampling day immediately on waking and again 15 and 30 min later. Self-rated psychological assessments of state levels of stress, arousal and fatigue were performed in the evening of each sampling day. A within-subjects repeated-measures analysis of participants who completed the course (12 of the original 20) showed a significant main effect of cortisol concentration across all three sampling points after awakening (F((2,22))=54.516, p<0.0001) and a significant main effect of weeks into the training course (F((3,33))=4.390, p=0.010). Further analysis of this effect of measurement-week revealed that at weeks 3 and 6 total cortisol secretion estimated by area under the curve was lower (F((3,33))=4.602, p=0.008) compared to the beginning and end of the course. Surprisingly self-reported stress, arousal and fatigue did not differ significantly across weeks, despite the large dropout rate (40%) and self-evident pressures of the course. We conclude that when controlling for many confounding variables, including participant adherence, post-awakening cortisol levels are sensitive to stressful challenge over a period of weeks.

Changes in basal hypothalamo-pituitary-adrenal activity during exercise training are centrally mediated

The effects of exercise training on hypothalamo-pituitary-adrenal (HPA) function are unclear. We investigated whether pituitary-adrenal adaptation during exercise training is mediated by changes in neuropeptide and corticosteroid receptor gene expression in the brain and pituitary. Sprague-Dawley rats were subject to either daily swimming (DS) or sham exercise (SE) for 45 min/day, 5 days/week, for 2 (2W), 4 (4W), or 6 wk (6W) ( n = 7–10/group). Corticosterone (Cort) and catecholamine responses during swimming were robust at 6W compared with 2W and 4W, indicating that HPA response to exercise during training is not attenuated when absolute intensity is progressively increased. In DS, basal (morning) plasma ACTH and Cort levels increased from 2W to 4W but plateaued at 6W, whereas in SE, they increased from 4W to 6W, with 6W values higher than in DS. In DS, there was a transient decrease in glucocorticoid receptor (GR) mRNA in the paraventricular nucleus (PVN) and pituitary and a transient increase in corticotrophin-releasing hormone (CRH) mRNA. In contrast, hippocampal mineralocorticoid receptor mRNA and PVN GR mRNA decreased from 4W to 6W in SE, with 6W values lower than in DS. These findings suggest that exercise training prevents an elevation in basal pituitary-adrenal activity potentially via transient alterations in the gene transcription of PVN and pituitary GR as well as CRH to suppress central drive to the HPA axis. In contrast, the increase in basal pituitary-adrenal activity with repeated sham exercise appears to be associated with decreases in hippocampal MR and PVN GR mRNA expression.

The overtraining syndrome in athletes: a stress-related disorder

Physical exercise is a type of allostatic load for several endocrine systems, notably the hypothalamic-pituitary-adrenal (HPA) axis. Athletes undergoing a strenuous training schedule can develop a significant decrease in performance associated with systemic symptoms or signs: the overtraining syndrome (OTS). This is a stress-related condition that consists of alteration of physiological functions and adaptation to performance, impairment of psychological processing, immunological dysfunction and biochemical abnormalities. Universally agreed diagnostic criteria for OTS are lacking. The pituitary-adrenal response to a standardized exercise test is usually reduced in overtrained athletes. This HPA dysfunction could reflect the exhaustion stage of Selye's general adaptation syndrome. The most attractive hypothesis that accounts for the observed neuro-endocrine-immune dysregulation is the Smith's cytokine hypothesis of OTS. It assumes that physical training can produce muscle and skeletal trauma, thus generating a local inflammatory reaction. With the excessive repetition of the training stimulus the local inflammation can generate a systemic inflammatory response. The main actors of these processes are the cytokines, polypeptides that modulate HPA function in and outside the brain at nearly every level of activity. It is hoped that future research will focus on endogenous risk factors for morbidities related to the neuro-endocrine-immune adaptation to exercise.

Prolonged daytime exercise repeated over 4 days increases sleeping heart rate and metabolic rate

The aim of this study was to determine the influence of prolonged exercise repeated for 4 days on sleeping heart rate (SHR) and metabolic rate (SMR). Eleven young untrained men exercised at moderate intensity 5 hrs daily for 4 days, alternately on a cycle ergometer (57.0 +/- 1.3% .VO2max) and a treadmill (64.7 +/- 1.6% .VO2max). They spent the night prior to the exercise period (control, C) and the 4 nights following exercise days (N1 to N4) in room calorimeters for the measurement of SHR, SMR, and respiratory quotient (RQ) from midnight until 6 a.m. Every morning, before the exercise bouts, plasma-free epinephrine (E) and norepinephrine (NE) levels were measured. After exercise, all SHR values were significantly higher than at C level (52 +/- 1 bpm, p < 0.001) and the highest value was observed on N2 (61 +/- 2 bpm). SMR increased by 11.2 +/- 1.5% from C to N1, p < 0.001, and then plateaued up to N4, whereas RQ decreased from C (0.833 +/- 0.009) to N2 (0.798 +/- 0.005) and then plateaued. Plasma NE levels were higher the morning after each day of exercise and peaked on N2, whereas no significant variations were found for E. Variations of SHR between C and N2, and N3 and N4 were correlated with changes of SMR. No significant relationships were found between morning plasma NE, and either SMR or SHR variations. To conclude, prolonged exercise repeated for 4 days was associated with increases in SHR and SMR during the night following each day of exercise concomitantly with an enhanced lipid oxidation. The sustained stimulation of the sympathetic nervous system may be partly responsible for these effects.

Human albumin synthesis is increased by an ultra-endurance trial

PURPOSE

The purpose of this study was to determine whether an ultra-endurance event is a strong stimulus to increase albumin synthesis involved in the process of intravascular albumin mass increase associated with transient hypervolemia.

METHODS

The albumin synthetic rate was measured in six young men, 3 d before (C) and on the 1st (R1) and 8th (R8) days of the recovery from an ultra-endurance trial (5 h daily for 4 d). Albumin fractional (FSR) and absolute (ASR) synthetic rate were determined using a primed-constant infusion of [1(-13) C] leucine. Plasma volume (PV) using Evans Blue dye dilution and total body water (TBW) using bioelectrical impedance analysis were measured on C, R1, and R8.

RESULTS

On R1 as compared with C: 1). PV (+23.3 +/- 3.2%; P<or= 0.001) and TBW (+4.2 +/- 0.8%; P<or= 0.01) expanded; 2). FSR and ASR both increased from 5.36 +/- 0.46 to 6.86 +/- 0.62%.24 h (+ 29.0 +/- 7.1%; P<or= 0.01) and from 103 +/- 10 to 153 +/- 19 mg.kg body weight (-1).24 h (-1) (+47.5 +/- 6.8%; P<or= 0.01); and 3). plasma albumin and protein masses increased (P<or= 0.05) from 1.92 +/- 0.08 to 2.22 +/- 0.14 g.kg body weight (-1) (i.e., +15.3 +/- 4.9%) and from 3.15 +/- 0.18 to 3.56 +/- 0.21 g.kg body weight (-1) (+13.3 +/- 3.9%), respectively. By R8, all these parameters had returned to their control levels except for albumin mass (1.73 +/- 0.08 g.kg body weight(-1), which was lower than C ( P<or= 0.05).

CONCLUSION

The increase in the albumin synthetic rate the day after an ultra-endurance trial is a major event associated with a greater circulating protein mass. The impact of exercise on albumin synthesis has disappeared 8 d later, as did PV and total protein mass expansion.

The unknown mechanism of the overtraining syndrome: clues from depression and psychoneuroimmunology

When prolonged, excessive training stresses are applied concurrent with inadequate recovery, performance decrements and chronic maladaptations occur. Known as the overtraining syndrome (OTS), this complex condition afflicts a large percentage of athletes at least once during their careers. There is no objective biomarker for OTS and the underlying mechanism is unknown. However, it is not widely recognised that OTS and clinical depression [e.g. major depression (MD)] involve remarkably similar signs and symptoms, brain structures, neurotransmitters, endocrine pathways and immune responses. We propose that OTS and MD have similar aetiologies. Our examination of numerous shared characteristics offers insights into the mechanism of OTS and encourages testable experimental hypotheses. Novel recommendations are proposed for the treatment of overtrained athletes with antidepressant medications, and guidelines are provided for psychological counselling.

Resistance exercise overtraining and overreaching. Neuroendocrine responses

Overtraining is defined as an increase in training volume and/or intensity of exercise resulting in performance decrements. Recovery from this condition often requires many weeks or months. A shorter or less severe variation of overtraining is referred to as overreaching, which is easily recovered from in just a few days. Many structured training programmes utilise phases of overreaching to provide variety of the training stimulus. Much of the scientific literature on overtraining is based on aerobic activities, despite the fact that resistance exercise is a large component of many exercise programmes. Chronic resistance exercise can result in differential responses to overtraining depending on whether either training volume or training intensity is excessive. The neuroendocrine system is a complex physiological entity that can influence many other systems. Neuroendocrine responses to high volume resistance exercise overtraining appear to be somewhat similar to overtraining for aerobic activities. On the other hand, excessive resistance training intensity produces a distinctly different neuroendocrine profile. As a result, some of the neuroendocrine characteristics often suggested as markers of overtraining may not be applicable to some overtraining scenarios. Further research will permit elucidation of the interactions between the neuroendocrine system and other physiological systems in the aetiology of performance decrements from overtraining.

beta-Endorphin and adrenocorticotrophin after incremental exercise and marathon running--female responses

Investigations of exercise-induced increases in beta-endorphin, adrenocorticotropic hormone (ACTH) and cortisol concentration have been carried out mainly in men. Data concerning the female reaction are sparse and less clear. In a comparison between incremental exercise and marathon running 14 experienced female marathon runners volunteered to run to exhaustion according to an incremental treadmill protocol. They ran a marathon 4 weeks later. Blood was analysed for beta-endorphin, ACTH and cortisol concentration immediately prior to the laboratory treadmill test, 3, 30 and 60 min later, as well as prior to the marathon, after 60 min and 120 min of running and 3, 30 min, and 24 h after completion of the run. At each blood collection, lactate concentration, heart frequency and perceived exertion were determined. The mean marathon running time was 3.22 h. Baseline concentrations for beta-endorphin of 22 pmol.l-1 before the marathon and 19 pmol.l-1 before the treadmill exercise increased 1.4-fold 30 min after the marathon and 1.9-fold after the treadmill exercise; for ACTH the baseline of 4.7 and 4.0 pmol.l-1 was increased by 8.3- and 10.3-fold, respectively. Cortisol concentration rose exponentially from a baseline 17 micrograms.dl-1 and peaked at 2.2-fold 30 min after the run, when the maximal concentration also had been reached after the treadmill test, increasing 1.3-fold from a baseline of 21 micrograms.dl-1. The maximal values for cortisol concentration after both exercises differed from each other, while the maxima of ACTH and beta-endorphin concentrations were similar. The ACTH and beta-endorphin concentration declined more slowly during the recovery after the marathon than after the treadmill. Cortisol concentration was below baseline 24 h later. In comparison with men studied earlier, female marathon runners showed higher baseline concentrations and lesser increases in beta-endorphin and lower baseline concentrations and larger increases in ACTH concentration after both types of exercise. The delayed decrease in concentration of the hormones after the marathon was similar in male and female runners.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.