Variation in bone mineral content and estimated body fat in young adult females

Variation in bone mineral content and estimated body fat in young adult females. Med. Sci. Sports Exerc, Vol. 22, No. 5, pp. 564-569, 1990. This study was designed to determine whether variability in bone mineral content (BMC) at the lumbar vertebrae (L2-4), radius shaft (RS), femoral neck, and distal radius can significantly contribute to the variability observed in body density (Db) among 89 females (age = 25.1 ± 5.3 yr) of varying activity levels and menstrual status. Theoretical differences in Db were calculated at ±1 and ±2 standard deviations of BMC (SD_bmc) for the population as well as for the subgroups: eumenorrheic inactive controls (C), recreational runners (RR), collegiate runners (CR), body builders (BB), swimmers (S), and amenorrheic runners (AR). Multiple regression to predict Db yielded significant coefficients (b) for BMC at L2-4 (b = 0.0190, P < 0.001) and RS (b = 0.0425, P< 0.01) when added separately to the sum of four skinfolds (subscapula, abdomen, thigh, calf). The differences in % BF_hw at ±1 and ±2 SD_bmc for the sample mean for RS_bmc were ±1.0% and ±2.0%, respectively. Variability in L2-4 contributed differences of ±1.3% and ±2.6% at ±1 and ±2 SD_bmc. The subgroup % BFhw differences (due to L2-4 and RS combined) ranged from an average overestimation of 1.3% for the AR to an average underestimation of 1.4% for the BB. Estimated mean errors for remaining groups were ≤ 0.5%. Individual differences ranged from a 3.3% underestimation (BB) to a 3.0% overestimation (AR). It is concluded that variability in BMC among young adult females may significantly contribute to variability in Db, independent of fatness. While the impact of high or low bone mineral content on %BF_hw is modest for most individuals, those athletes with extremely high or low BMC values may require adjustments in the equations used to convert Db to %BF. It is suggested that correlations between Db and total BMC (or BM density) be evaluated in a similar manner as presented here before stronger conclusions can be made concerning the impact of bone on estimations of %BF.