Successful 6-Month Endurance Training Does Not Alter Insulin-Like Growth Factor-I in Healthy Older Men and Women

Background. Lean body mass, strength, and endurance decline with advancing age, changes paralleled by declines in anabolic hormones, including growth hormone (GH) and insulin-like growth factor-I (IGF-I). Acute exercise has been shown to stimulate the GH/IGF-I axis, and long-term exercise increases GH. This study examined the effect of endurance training on IGF-I in healthy older men and women. Methods. Thirty-one healthy older men (66.9 ± 1.0 yrs, mean ± SEM) and 21 healthy older women (67.1 ± 1.7 yrs) were randomized to either 3d/wk, 6-month endurance (ET3) or stretching/flexibility (SF3) protocols. Another group of 15 healthy older men (69.0 ± 1.3 yrs) participated in a more intensive 5d/wk, 6-month endurance protocol (ET5). Before and after training, subjects were weight stabilized and participated in maximal exercise tolerance testing, body composition assessment, and fasting blood sampling. Results. ET3 training resulted in a significant increase (14%) in maximal aerobic power (V̇02max), significant decreases in body weight (BW), fat mass (FM), and waist/hip ratio (WHR), and a significant increase in fat-free mass (FFM). No significant V̇02max or body composition changes were observed in the SF3 group. For the ET5 group, a significant increase (22%) in V̇02max and significant decreases in BW, FM, and WHR were observed. No significant changes in IGF-I were observed for any of the three groups. Pre- versus post-training IGF-I values were very stable (r = .86, p < .001) across subjects. Conclusions. Within-subject basal levels of IGF-I in healthy seniors were extremely stable between pre- and posttraining assessments. Two endurance training protocols of magnitudes sufficient to significantly increase aerobic capacity and decrease measures of body adiposity did not significantly increase basal levels of IGF-I in healthy older men and women.