Objectives: Overtraining syndrome (OTS) leads to worsened sports performance and fatigue. The pathophysiology of OTS has not been entirely elucidated, and there is a lack of accurate markers for its diagnosis. Changes in hormonal responses implicated in OTS were stimulated by exercise, which has limited their interpretation. Hence, we aimed to evaluate growth hormone (GH) and prolactin responses to a gold-standard and exercise-independent stimulation test, the insulin tolerance test (ITT).
Design: Volunteers were recruited and divided into OTS-affected athletes (OTS), healthy athletes (ATL), and healthy non-active subjects (NCS) groups, after general and specific inclusion and exclusion criteria.
Methods: We evaluated the responses of growth hormone (GH) and prolactin to the ITT, and compared between groups.
Results: A total of 51 subjects were included (OTS, n=14, ATL, n=25, and NCS, n=12). OTS disclosed significantly lower basal levels of GH (p=0.003) and prolactin (p=0.048), and GH (p=0.001) and prolactin (p<0.001) responses to ITT (p=0.001), compared to ATL, but similar to NCS. OTS showed a later rise in GH levels in response to hypoglycemia, compared to ATL, but not to NCS. We suggest cutoffs for GH and prolactin levels to aid in the diagnosis of OTS.
Conclusions: OTS-affected athletes show reduced GH and prolactin basal levels and responses to a non-exercise stress test compared to healthy athletes, but not to sedentary subjects.
Keywords: GH; Insulin tolerance test; Overtraining syndrome; Prolactin; Sports endocrinology.
Copyright © 2017. Published by Elsevier Ltd.