In 1997, Vitiello, et. al., conducted study which deals with individuals age, there is a natural decline in lean body mass, strength, and endurance, accompanied by a reduction in anabolic hormones such as growth hormone (GH) and insulin-like growth factor-I (IGF-I). While acute exercise has been shown to stimulate the GH/IGF-I axis, the long-term effects of exercise on IGF-I in the elderly population remain a subject of interest. This study aimed to investigate the impact of 6 months of endurance training on IGF-I levels in healthy older men and women.

Thirty-one healthy older men (mean age 66.9 ± 1.0 years) and 21 healthy older women (mean age 67.1 ± 1.7 years) were randomly assigned to either a 3-day-per-week, 6-month endurance training (ET3) group or a stretching/flexibility (SF3) group. Additionally, 15 healthy older men (mean age 69.0 ± 1.3 years) participated in a more intensive 5-day-per-week, 6-month endurance training (ET5) protocol. Before and after the training period, participants underwent maximal exercise tolerance testing, body composition assessment, and fasting blood sampling.

The ET3 group exhibited a significant 14% increase in maximal aerobic power (VO2max), along with significant decreases in body weight (BW), fat mass (FM), and waist/hip ratio (WHR), accompanied by a significant increase in fat-free mass (FFM). Conversely, the SF3 group showed no significant changes in VO2max or body composition. The ET5 group displayed a notable 22% increase in VO2max and significant decreases in BW, FM, and WHR. However, none of the three groups showed significant changes in IGF-I levels. The pre- versus post-training IGF-I values remained remarkably stable across subjects (r = .86, p < .001).

This study revealed that basal levels of IGF-I in healthy seniors remained highly stable between pre- and post-training assessments. Despite the substantial improvements in aerobic capacity and reductions in measures of body adiposity achieved through two different endurance training protocols, there was no significant increase in basal levels of IGF-I in healthy older men and women. These findings emphasize the complexity of the relationship between endurance training and the IGF-I axis in the aging population.

Reference: Vitiello, M. V., Wilkinson, C. W., Merriam, G. R., Moe, K. E., Prinz, P. N., Ralph, D. D., & Schwartz, R. S. (1997). Successful 6-month endurance training does not alter insulin-like growth factor-I in healthy older men and women. The Journals of Gerontology Series A: Biological Sciences and Medical Sciences, 52(3), M149-M154.