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


METHODS
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.
Military Performance Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760, USA. cassi.strohbach@us.army.mil
C A
CA
Strohbach
D E
DE
Scofield
B C
BC
Nindl
A J
AJ
Centi
R
R
Yanovich
R K
RK
Evans
D S
DS
Moran
D000293:Adolescent; D004493:Education; D005260:Female; D015775:Fractures, Stress / Q000378:metabolism*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000097:blood; D018976:Insulin-Like Growth Factor Binding Protein 6 / Q000097:blood*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008889:Military Personnel; D055815:Young Adult
D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D018972:Insulin-Like Growth Factor Binding Protein 3; D018975:Insulin-Like Growth Factor Binding Protein 5; D018976:Insulin-Like Growth Factor Binding Protein 6; D007334:Insulin-Like Growth Factor I