Bone Mineral Content/Density And Muscle Strength In Young Women From Different Racial/Ethnic Backgrounds - A Pilot Study

Abstract

Race/ethnicity is a major factor influencing both bone mass and muscle mass (bone free lean mass - BFLM) since muscular forces can enhance bone strength by applying mechanical stress to the skeleton. PURPOSE: To examine group mean differences and the relationships between bone mineral content (BMC) and density (BMD) to BFLM and muscle strength in young women from different racial/ethnic backgrounds. METHODS: Twenty-seven young women aged 18-30 years self-identified themselves as Caucasian (Cau; n=6), South-Asian (SA; n=6), East-Asian (EA; n=4), Hispanic (His; n=6), and African-American (AA; n=5). Body composition (fat, BFLM, and BMC) and total and regional BMD were measured using Dual Energy X-Ray Absorptiometry, while jump test, leg press, and bilateral isokinetic strength testing of knee flexors/extensors were used to quantify lower limb muscle strength and power. International Physical Activity Questionnaire (IPAQ) classified women into low, moderate or high levels of physical activity. Ethnic differences in each outcome variable were determined using one-way ANOVA, while Pearson correlation coefficients quantified relationships between variables. Statistical significance was set at p < 0.05. RESULTS: Based on the entire sample (n=27), both total body BMD and BMC had significant positive relationships with total BFLM (r=0.78 and 0.87 respectively). Based on ethnicity, AA women had significantly higher total body and hip (left and right) BMC than His. Although non-significant, total BFLM values were highest for AA and lowest for EA and SA (47.7±9.6 kg vs. 37.9±5.5 kg and 37.8±5.5 kg respectively; p=0.08). Analysis of the entire sample revealed a significant positive relationship between MET minutes/week and total BFLM (r=0.45). As per IPAQ scores, highly active women had significantly lower percent body fat compared to moderately active women (26% ± 6% vs. 38% ± 7%; p=0.001). Finally, average muscular power (watts; W) during flexion at 60 deg/sec was significantly higher for Cau compared to EA and SA (54.98±18.74 W vs. 30.76±7.6 W and 27.7±9.0 W respectively; p=0.01). CONCLUSION: These findings suggest that BMC and BMD are significantly related to total BFLM, and that BMC varies across the ethnic groups, however, further data collection and analyses will validate the current findings.