Interrelationships between body mass to waist circumference ratio,body mass index,and total body muscularity in older women

PurposeTo examine the relationships between body mass to waist circumference (BM:W) ratio or body mass index (BMI) and muscularity, 140 overweight (BMI ≥ 25 kg/m² and <30 kg/m²), 265 normal weight (BMI > 18.5 kg/m² and <25 kg/m²) and 26 underweight (BMI ≤ 18.5 kg/m²) Japanese women aged 60–80 years volunteered (overall 431 women).MethodsMuscle thickness was measured by ultrasound at six sites on the anterior and posterior aspects of the body. Total muscle mass (TMM) was estimated from an ultrasound-derived prediction equation. BMI and BM:W ratio were calculated using anthropometrical variables.ResultsWhen the overall sample was used, BMI was positively correlated with the TMM (r = 0.573, p < 0.001) and TMM index (r = 0.659, p < 0.001). BM:W ratio was also positively correlated with the TMM (r = 0.566, p < 0.001) and TMM index (r = 0.400, p < 0.001). In normal weight women, BMI was positively correlated with the TMM (r = 0.460, p < 0.001) and TMM index (r = 0.496, p < 0.001). Similarly, BM:W ratio was positively correlated with the TMM (r = 0.514, p < 0.001) and TMM index (r = 0.318, p < 0.001). In overweight and underweight women, TMM was significantly and positively correlated with BM:W ratio (r = 0.442 and r = 0.715, respectively; p < 0.001), but not BMI (r = 0.077 and r = 0.315). TMM index was also positively correlated with BM:W ratio in both overweight (r = 0.184, p < 0.05) and underweight (r = 0.500, p < 0.01) women. BMI was positively correlated with TMM index (r = 0.230, p < 0.01) and inversely correlated to the percentage of TMM in body mass (r = −0.262, p < 0.01) in overweight women.ConclusionThese results suggest that, compared to BMI, BM:W ratio may provide a simple and potential index for assessing muscularity in Japanese older underweight women. However, in normal and overweight women, BMI and BM:W ratio are both preferred in assessing muscularity.