Effect of training on the GH/IGF-I axis during exercise in middle-aged men: relationship to glucose homeostasis

Metabolic Unit, 1 Service Central de Physiologie Clinique: Centre d'Exploration et de Réadaptation des Anomalies Métaboliques et Musculaires, and 2 Service de Médecine Nucléaire, hôpital Lapeyronie, 34295 Montpellier; and 3 Service de Biochimie B, Centre Hospitalier Universitaire, Saint Eloi, 34295 Montpellier, France The aim of this study was to compare circulating levels of growth hormone (GH), IGF-I, and IGF-binding protein (IGFBP)-1 and IGFBP-3 in response to a long-duration endurance exercise in trained vs. sedentary middle-aged males and to determine whether a relationship with glucose homeostasis exists. Seven trained men (Tr) were compared with seven age-matched sedentary men (Sed) during two trials of 60 min of cycling exercise performed below ( VT) and above (+VT) the ventilatory threshold. Insulin sensitivity (S I ) was higher in Tr than in Sed ( P