(43) Fat free mass index is positively related to bone mineral density and resting metabolic rate in NCAA Division I wrestlers

Purpose: Weight class sports, such as wrestling, require athletes to cut weight in order to compete in their assigned weight class. As a result, wrestlers will restrict fluid and caloric intake while increasing exercise energy expenditure to “make weight”. Caloric restriction and increased energy expenditure can result in bone loss, fat free mass (FFM) loss, and altered metabolism. Thus, the purpose of the present study was to investigate the relationships between the difference between typical body mass and weight class (Δmass), body fat percent (BF%), FFM index (FFMI), FFM, resting metabolic rate (RMR), and bone mineral density (BMD). Methods: Data from 32 National Collegiate Athletic Association (NCAA) Division I wrestlers from a Midwestern school were analyzed. Data was collected during the pre-season prior to minimum weight class certifications. Height and weight were measured using a stadiometer to the nearest 0.1 cm and medical grade scale to the nearest 0.1 kg, respectively. Wrestlers were then asked to sit for 25 minutes before beginning RMR assessment via a metabolic cart. RMR was collected for 30 minutes, using the first 10 as familiarization and the last 20 for analysis. Following RMR, wresters underwent body composition analysis via dual-energy x-ray absorptiometry. BF% and bone density were recorded. FFM was calculated from BF% and FFMI was calculated as kg of FFM/m². Finally, Δmass was calculated by finding the difference between typical body mass, as measured by the medical grade scale, and reported weight class. This measure is reported in pounds as the NCAA weight classes are identified as pounds. Pearson correlation coefficients were used to determine relationships between body composition variables, RMR, and bone mineral density. Significance was set to p< 0.05. Results: Participant characteristics are available in Table 1. FFMI was positively correlated with RMR (r=0.375; p=0.034), BMD (r=0.476; p=0.006), and Δmass (r=0.631; p< 0.001). Δmass was positively correlated with BF% (r=0.397; p=0.24) and FFM (r=0.413; p=0.019). Finally, FFM was positively correlated with RMR (r=0.380; p=0.032) and BMD (r=0.547; p=0.001). Conclusions: FFMI may have a positive influence on RMR and BMD in NCAA DI wrestlers. Further, greater FFM was associated with larger Δmass. Interestingly, larger Δmass was associated with greater RMR, FFMI, and FFM. The relationship is unexpected however may change as the season progresses. Practical Applications: It is recommended practitioners working with wrestlers monitor changes in body composition, RMR, and BMD through the season to avoid any negative health outcomes associated with energy restriction and increased energy expenditure. Further, future research should monitor these relationships longitudinally. Acknowledgements: None