Reproductive health and stress fracture risk: a wearables solution

Abstract

Introduction: Insulin-like growth factor 1 (IGF-I) is a mitogenic and metabolic growth factor that can act both systemically and locally, being produced predominantly in the liver but also by other tissues including the brain, kidneys, muscle, and bone1,2. IGF-I is well-established as an important mediator of bone formation, remodelling, and repair and can be easily measured in serum. IGF-I stimulates osteoblast proliferation, bone matrix protein synthesis, alkaline phosphatase activity and differentiation. Loss of IGF-I results in decreased long bone size, reduced growth plates, and delayed formation of secondary ossification centers in mice. Conversely, transgenic mice with osteoblast-targeted overexpression of IGF-I demonstrate an accelerated bone formation rate with increased bone mineral density (BMD) and trabecular and cortical bone volume. The essential nature of IGF-I in bone development is recapitulated in humans. Individuals with disruptions in the IGF-I gene causing reduced serum IGF-I concentrations have a severe reduction in peak BMD compared to normal age-matched individuals. Methods: This presentation will provide an overview of the relationship between the IGF-I system and bone health and remodelling, with a particular emphasis toward military relevance and utility of measuring IGF-I during military training2,3. Because the IGF-I system is involved in bone formation, remodelling, and repair, female recruits sustaining stress fractures during military training would be of special interest with regard to differential circulating concentrations of IGF-I system components compared to their uninjured female counterparts. Moreover, serum measurements of the IGF-I system could possibly provide further insight into stress fracture injury risk. Conclusions: Preliminary data3 suggest that circulating IGF-I system components are differentially expressed in females sustaining stress fractures during military BT. Additionally, data suggest that the bioavailable IGF-I response to strenuous exercise may differ in female recruits susceptible to stress fracture injury when compared to non-injured recruits. This suggests the possibility that increased susceptibility to stress fracture injury may be attributed to differences in the IGF-I system response to physical training (i.e., increased susceptibility to stress fracture may be due to a blunted bioavailable IGF-I response to training or increased basal levels of certain IGFBPs). However, the underlying mechanism for the differences in IGF-I system component concentrations between recruits sustaining stress fractures and uninjured counterparts is still unclear and warrants further investigation. References 1Nindl BC, Pierce JR. Insulin-like growth factors I as a biomarker of health, fitness, and training status. Med Sci Sports Exerc 2010; 42(1):39-49. https://doi.org/10.1249/mss.0b013e3181b07c4d 2Nindl BC, McClung JP, Miller JK, et al. Bioavailable IGF-I is associated with fat-free mass gains after physical training in women. Med Sci Sports Exerc 2011; 43(5):793-799. https://doi.org/10.1249/MSS.0b013e31820065.ea 3Strohbach CA, Scofield DE, Nindl BC, et al. Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: a preliminary study. Growth Horm IGF Res 2012; 22(5):151-157. https://doi.org/10.1016/j.ghir.2012.04.007