An imbalance between the overall strain experienced during exercise training and the athlete's tolerance of such effort may induce overreaching or overtraining syndrome. Overtraining syndrome is characterised by diminished sport-specific physical performance, accelerated fatiguability and subjective symptoms of stress. Overtraining is feared by athletes yet there is a lack of objective parameters suitable for its diagnosis and prevention. In addition to the determination of substrates (e.g. lactate, ammonia and urea) and enzymes (e.g. creatine kinase), the possibilities for monitoring of training by measuring hormonal levels in blood are currently being investigated. Endogenous hormones are essential for physiological reactions and adaptations during physical work and influence the recovery phase after exercise by modulating anabolic and catabolic processes. Testosterone and cortisol are playing a significant role in metabolism of protein as well as carbohydrate metabolism. Both are competitive agonists at the receptor level of muscular cells. The testosterone/cortisol ratio is used as an indication of the anabolic/catabolic balance. This ratio decreases in relation to the intensity and duration of physical exercise, as well as during periods of intense training or repetitive competition, and can be reversed by regenerative measures. Correlations have been noted with the training-induced changes of strength. However, it seems more likely that the testosterone/cortisol ratio indicates the actual physiological strain in training, rather than overtraining syndrome. The sympatho-adrenergic system might be involved in the pathogenesis of overtraining. Overtraining appears as a disturbed autonomic regulation, which in its parasympathicotonic form shows a diminished maximal secretion of catecholamines, combined with an impaired full mobilisation of anaerobic lactic reserves. This is supposed to lead to decreased maximal blood lactate levels and maximal performance. Free plasma adrenaline (epinephrine) and noradrenaline (norepinephrine) may provide additional information for the monitoring of endurance training. While prolonged aerobic exercise conducted at intensities below the individual anaerobic threshold lead to a moderate rise of sympathetic activity, workloads exceeding this threshold are characterised by a disproportionate increase in the levels of catecholamines. In addition, psychological stress during competitive events is characterised by a higher catecholamines to lactate ratio in comparison with training exercise sessions. Thus, the frequency of training sessions with higher anaerobic lactic demands or of competition, should be carefully limited in order to prevent overtraining syndrome. In the state of overtraining syndrome and overreaching, respectively, an intraindividually decreased maximum rise of pituitary hormones (corticotrophin, growth hormone), cortisol and insulin has been found after a standardised exhaustive exercise test performed with an intensity of 10% above the individual anaerobic threshold.(ABSTRACT TRUNCATED AT 400 WORDS)

Blood Hormones as Markers of Training Stress and Overtraining

Over 30 years ago Sir David Barker first proposed the theory that events in early life could explain an individuals' risk of non-communicable disease in later life; the Developmental Origins of Health and Disease (DOHaD) theory. During the 1990s the validity of the DOHaD theory was extensively tested in a number of human populations and the mechanisms underpinning it characterised in a range of experimental animal models. Over the past decade, researchers have sought to use this mechanistic understanding of DOHaD to develop therapeutic interventions during pregnancy and early life to improve adult health. A variety of animal models have been used to develop and evaluate interventions, each with strengths and limitations. It is becoming apparent that effective translational research requires that the animal paradigm selected mirrors the tempo of human fetal growth and development as closely as possible so that the effect of a perinatal insult and/or therapeutic intervention can be fully assessed. The guinea pig is one such animal model that over the past two decades has demonstrated itself to be a very useful platform for these important reproductive studies. This review highlights similarities in the in utero development between humans and guinea pigs, their strengths and limitations as an experimental model of DOHaD and their potential to enhance clinical therapeutic innovation to improve human health. This article is protected by copyright. All rights reserved.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/JP274948

Guinea pig models for translation of the developmental origins of health and disease hypothesis into the clinic.

Purpose The aims of this paper are to briefly review the types of animal and tumor models used in carcinogenesis studies and to consider their utility in studies of physical activity and cancer. Methods Published data from animal studies using tumor models for which corresponding human epidemiologic evidence shows a clear association between physical activity and that cancer (i.e., colon and breast) are reviewed. Results A variety of animal-tumor models have been used in cancer studies including spontaneous tumors, chemically induced tumors, orthotopic and syngeneic tumor transplantation, injected tumors, and genetically engineered (transgenic, knockout, and mutation-induced) mice with a predisposition to neoplasia. The most commonly used animal-tumor model in the study of physical activity has been the chemical carcinogenesis model. Methodological limitations of the various animal-tumor models are described including variations in dosing, route of administration, and type of carcinogen used, and forced versus voluntary exercise effects. Conclusions Animal-tumor models are useful for understanding specific aspects of the carcinogenesis process and the interaction of this process with exercise. There is no one animal-tumor model that is ideally suited for studying physical activity interventions. However, animal-tumor models can be viewed as complementary to epidemiologic studies and human clinical trials in the area of physical activity and cancer prevention.

Physical activity and cancer prevention: animal-tumor models.

Influence of muscle use on protein synthesis and degradation.

Surface EMG and torsion measurements during snow skiing: laboratory and field tests

We examined the changes induced by daily treadmill exercise on body weights, plantaris muscle weights, plantaris protein concentrations, andl-leucine-4,5-3H incorporation into plantaris muscles of normal and castrated young male guinea pigs and of castrated animals receiving testosterone replacement therapy, and compared the testosterone-1,2-3H uptake by plantaris muscles of trained normal guinea pigs to that of untrained animals. Trained animals exhibited significantly lower body and muscle weights and greater labeled leucine incorporation into sarcoplasmic and myofibrillar proteins but did not show significant changes in protein concentrations or labeled testosterone uptake. The level of physical activity of the young animals studied appeared to be more important than gonadal endocrine function in altering protein metabolism and muscle and body weights. Because hypertrophy did not occur in the trained plantaris muscles, which had elevated rates of labeled leucine incorporation, it appears that the trained animals had a higher muscle protein turnover rate. It seems unlikely that testosterone plays an important role in these activity-related phenomena.

J. Scala

Papers

Skeletal muscle leucine incorporation and testosterone uptake in exercised guinea pigs.