Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: A preliminary study

• Published in: Growth hormone & IGF research 2012-10, Vol.22 (5), p.151-157
• Main Authors: Strohbach, C.A, Scofield, D.E, Nindl, B.C, Centi, A.J, Yanovich, R, Evans, R.K, Moran, D.S
• Format: Article
• Language: English
• Subjects: Adolescent; Advanced Basic Science; Education; Endocrinology & Metabolism; Female; Fractures, Stress - metabolism; Humans; Insulin-like growth factor binding protein; Insulin-Like Growth Factor Binding Protein 1 - blood; Insulin-Like Growth Factor Binding Protein 2 - blood; Insulin-Like Growth Factor Binding Protein 3 - blood; Insulin-Like Growth Factor Binding Protein 5 - blood; Insulin-Like Growth Factor Binding Protein 6 - blood; Insulin-Like Growth Factor I - metabolism; Insulin-like growth factor-I; Military Personnel; Military physical training; Stress fracture; Young Adult
• ISSN: 1096-6374; 1532-2238
• DOI: 10.1016/j.ghir.2012.04.007

Abstract Objective Stress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n = 13) during BT and female soldiers who did not (NSFX, n = 49). Design Female soldiers ( n = 62, 18.8 ± 0.6 yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1–6, BAP, calcium, CTx, IL1β, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc ( p ≤ 0.05). Results The SFX group was significantly taller and had lower BMI than NSFX ( p ≤ 0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT ( p ≤ 0.05). In both groups, total IGF-I increased pre to postBT (p ≤ 0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58 ± 0.58 ng/mL; postBT 0.39 ± 0.48; p ≤ 0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53 ± 0.37 ng/mL; postBT: 0.63 ± 0.45; p ≤ 0.05). Conclusions Our study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.