Hormonal responses to acute exercise, training and overtraining a review with emphasis on the horse

Abstract

Overtraining is an imbalance between training and recovery leading to symptoms associated with a neuroendocrine dysbalance called the overtraining syndrome, a disease characterized by behavioral, emotional and physical symptoms similar with depression. Although the prevalence of overtraining is high in human and equine athletes, at present no sensitive and specific test is available to prevent or diagnose overtraining. Nowadays, it is believed that combination of different (hormonal) parameters appear to be the best indicators of overtraining. Therefore, this review provides a summary of previous literature examining the response of the hypothalamic-pituitary-adrenal (HPA) axis and the growth hormone-insulin-like growth factor-I (GH-IGF-I) axis to acute and chronic exercise as well as overtraining in humans and horses. The exercise induced hormonal responses seem to be equal for the equine as well as the human athlete, which makes comparisons possible. Repeated bouts of exercise are suggested to provide a way to detect subtle changes in hormonal responses in the individual athlete, which may make them an important tool in detecting early overtraining. This should be combined with corticotropin releasing hormone (CRH) stimulation tests and basal ACTH and GH pulsatility determination. Further research is needed to establish the correct training intensity and rest period for the exercise test in equines.

Hormonal responses following eccentric exercise in humans

“…30,31 Specifically, regulatory mechanisms appear to be quickly reengaged after a mechanical overloading (resistance) exercise workout so that homeostasis is restored within 1 hour post exercise. 8 However, following muscledamaging exercise, a longer, highly orchestrated sequence of responses is activated, initially associated with an inflammatory and degenerative phase at the site of damage and followed by the myogenic differentiation and fusion of myoblasts to complete muscle regeneration.…”

Influência do treinamento aeróbio sobre o cortisol e glicose plasmáticos em equinos

“…Uma vez que certo limiar de esforço físico for ultrapassado, ocorrerá efeito sistêmico com envolvimento do sistema nervoso periférico e central, e especialmente o sistema nervoso autônomo simpático e o eixo hipotálamo-hipófise-adrenal (EHHA) são ativados (Graaf-Roelfsema et al, 2007).…”

“…Os resultados de alguns estudos Graaf-Roelfsema et al, 2007) indicaram que o treinamento pode afetar a concentração plasmática de cortisol antes, durante e após o exercício. Dessa maneira, essa variável fisiológica poderia contribuir como indicador confiável para avaliação da aptidão física (Ferlazzo et al, 2006).…”

“…De uma maneira geral, poucos estudos verificaram a resposta do EHHA em equinos destreinados que retornaram ao treinamento (Graaf-Roelfsema et al, 2007). O propósito deste estudo foi avaliar as alterações no cortisol e sua possível utilização como indicador para avaliação de equinos submetidos a treinamento.…”

Effect of temperament on cortisol response to a single exercise bout in Thoroughbred racehorses – short communication

“…Stress is one of the main triggers of the hypothalamic-pituitaryadrenocortical (HPA) axis, and therefore it is often assessed by the determination of cortisol concentrations. Exercise may induce an intensive stress reaction (Graaf-Roelfsema et al, 2007), and cortisol response to exercise has been reported in equine studies (Gordon et al, 2007;Petruse et al, 2015). Several studies have examined horses on treadmills (Malinowski et al, 2006;Gordon et al, 2007); however, this abnormal type of work might influence stress response even in accustomed horses (Sloet van Oldruitenborgh-Oosterbaan and Clayton, 1999).…”