Nutrition and Health Sciences, Department of


Date of this Version



International Journal of Sports Physiology and Performance, forthcoming 2017. Acceptance Date: November 17, 2016


© 2016 Human Kinetics, Inc. Used by permission.


Ultra-endurance athletes often accumulate an energy deficit when engaging in ultra-endurance exercise, and upon completion of the exercise, they exhibit endocrine changes that are reminiscent of starvation. However, it remains unclear whether these endocrine changes are a result of the exercise per se or secondary to the energy deficit, and more importantly, whether these changes can be attenuated by increased dietary intake. Our goal was to assess the relationship between changes in key metabolic hormones following ultra-endurance exercise and measures of energy balance. Metabolic hormones as well as energy intake and expenditure were assessed in 14 well-trained male cyclists who completed a 1,230-km ultra-endurance cycling event. After completion of the event, serum testosterone (-67±18%), insulin-like growth factor-1 (IGF-1) (-45±8%), and leptin (-79±9%) were significantly suppressed (p<0.001), and remained suppressed after a 12-h recovery period (p<0.001). Changes in IGF-1 were positively correlated with energy balance over the course of the event (r=0.65, p=0.037), which ranged from a 11,859 kcal-deficit to a 3,593 kcal-surplus. The marked suppression of testosterone, IGF-1, and leptin following ultra-endurance exercise is comparable to changes occurring during acute starvation. The suppression of IGF-1, but not that of other metabolic hormones, was strongly associated with the magnitude of the energy deficit, indicating that athletes who attained a greater energy deficit exhibited a more pronounced drop in IGF-1. Future studies are needed to determine whether increased dietary intake can attenuate the endocrine response to ultra-endurance exercise.