Humans with obesity exhibit impaired circulating total, but not free, IGF-1 response to acute endurance exercise

We investigated how obesity impacts the response of circulating insulin-like growth factor-1 (IGF-1) to a single bout of endurance exercise in humans with and without obesity. Blood samples were collected before exercise, at 15 and 40 min during a 45-min cycling session at 65% of heart rate reserve, and 15 min post-exercise. Serum levels of total IGF-1, free IGF-1, IGF binding proteins 1 (IGFBP-1) and 3 (IGFBP-3), growth hormone, and insulin were measured. Both total IGF-1 and IGFBP-3 serum concentrations increased significantly (p < 0.05) during exercise in the study participants without obesity but not in those with obesity, returning to basal levels immediately after exercise. There was a statistically significant main effect on the growth hormone response, with circulating levels being higher in participants without obesity (p < 0.05). No significant effects were observed for either free IGF-1 or IGFBP-1 serum concentrations in response to exercise in either group (p > 0.05). We conclude that humans with obesity have blunted serum total IGF-1 response during exercise. However, a concurrent attenuation in serum IGFBP-3 response, which regulates free (i.e., biologically active) IGF-1 in circulation, results in no change in circulating free IGF-1 levels during endurance exercise in individuals with obesity.