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 advan cing age, changes paralleled by declines in anabolic hormones, includi ng 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 tr aining on IGF-I in healthy older men and women. Methods. Thirty-one he althy 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 endu rance (ET3) or stretching/flexibility (SF3) protocols. Another group o f 15 healthy older men (69.0 +/- 1.3 yrs) participated in a more inten sive 5d/wk, 6-month endurance protocol (ET5). Before and after trainin g, subjects were weight stabilized and participated in maximal exercis e tolerance testing, body composition assessment, and fasting blood sa mpling. Results. ET3 training resulted in a significant increase (14%) in maximal aerobic power (VO(2)max), significant decreases in body we ight (BW), fat mass (FM), and wais/hip ratio (WHR), and a significant increase in fat-free mass (FFM). No significant VO(2)max or body compo sition changes were observed in the SF3 group. For the ET5 group, a si gnificant increase (22%) in VO(2)max and significant decreases in BW, FM, and WHR were observed. No significant changes in IGF-I were observ ed for any of the three groups. Pre- versus post-training IGF-I values were very stable (r = .86, p < .001) across subjects. Conclusions. Wi thin-subject basal levels of IGF-I in healthy seniors were extremely s table between pre- and posttraining assessments. Two endurance trainin g protocols of magnitudes sufficient to significantly increase aerobic capacity and decrease measures of body adiposity did not significantl y increase basal levels of IGF-I in healthy older men and women.