Regeneration After Ultra-Endurance Exercise

Abstract

Conclusions: The total amount of exercise research literature dealing with the neuro-endocrine system and recovery is extremely small. However, from what is available there does appear to be some tentative, preliminary conclusions that can be postulated. When the neuroendocrine system is subjected to the stress of exercise there is an acute reactive response (typically characterized by rapid, transit elevations in circulating hormonal concentrations). If adequate rest and recovery are allowed following this acute reactivity phase, then the hormonal responses adjust and return essentially to baseline l~vels relatively rapidly. The length of time of this phase appears to be a few minutes to a few hours in duration. However, if the acute reactivity response is followed with further increases in training stress too soon, or without some degree of rest-recovery between sessions, there is the onset of a more chronic reactivity response. This is characterized by more prolonged elevations in circulating hormonal levels. The length of this phase appears to be a few hours to a few days. Relative to exercise training this may be coinciding with the point where overload and over-reaching training are occurring in athletes (64). Short periods (i.e., just a few days) of exposure to this stress seem to be tolerated well, but extended period of exposure to this stress are counter-productive. However, if the training stress is pushed still further then a more pronounced chronic reactivity response that is characterized by suppressed circulating hormonal develops. This type of response may result in the development of some degree of aberrant, mal-adaptation at the neuro-endocrine gland, which may manifest itsel f in the form of a regulatory axis disruption. This late chronic phase response may involve neuro-endocrine alterations that can last for a long period of time (possibly weeks or months) unless an adequate period of regeneration is allowed to occur. This last chronic phase response most likely represents a point where exercise training is inducing "negative maladaptation" as opposed to a positive adaptation. Relative to the sportsman, this is the time where the athlete is most likely developing, or has developed, the "overtraining syndrome" (4 I). This hypothetical explanation is a "preliminary working model" which may serve as a framework from which other investigators can add or subtract to. This is also a very simple approach attempting to explain the nature of the neuro-endocrine system responses to the interaction between the degree of exercise training versus rest-recovery time. It is recognized that in reality, this is a highly complex, multi-factorial area where many facets are coming into play to affect the neuro-endocrine system's responses and adaptations. For example, the time-line for the changes of individual hormones (i.e., temporal relationship) through the proposed acute and chronic reactivity phase of the model is potentially highly variable. A great deal of future research is necessary in the area of exercise endocrinology to allow a more clear and full discernment and understanding of these interactions.