Muscle quality as a potential explanation of the metabolically healthy but obese and sarcopenic obese paradoxes.

BACKGROUND: Obesity has been associated with metabolic complications. However, two subgroups of obese individuals (namely "sarcopenic obese" and "metabolically healthy but obese" individuals) with low muscle mass appear to have a better metabolic profile. Despite having a lower muscle mass, these individuals appear to have higher muscle strength, suggesting higher muscle quality. Studies have reported insulin sensitivity to be related to muscle quality. Therefore, the aim of the present study was to test the hypothesis that low muscle mass was associated with better muscle quality in obese individuals.

METHODS: A total of 112 postmenopausal women aged between 50 and 77 years (means, 61±6 years) were recruited. Body composition (bioelectrical impedancemetry), muscle strength (hand dynamometer), and functional capacity (chair stand test, alternate step test and balance test) were measured.

RESULTS: Skeletal muscle mass (SM; kg) was significantly positively correlated with muscle strength (kg) in normal weight (r=0.43; P=0.003) and overweight (r=0.42; P=0.020) women, but not in obese (r=0.28; P=0.13) women. Muscle mass (kg) was significantly negatively correlated with muscle quality (kg/SMkg) in normal weight (r=-0.41, P=0.005), overweight (r=-0.59; P<0.001) and obese (r=-0.59; P<0.001) individuals. Skeletal muscle mass index (kg/m(2)) was significantly negatively correlated with muscle quality in normal weight (r=-0.33, P=0.025), overweight (r=-0.47, P=0.008), and obese (r=-0.43, P=0.015) women. Finally, type II sarcopenic individuals had higher muscle quality than type I sarcopenic (P=0.002) and nonsarcopenic (P=0.001) individuals.

CONCLUSIONS: Our results support our hypothesis and showed that muscle quality increased as muscle mass and muscle mass index decreased. Thus, muscle quality may potentially explain the favorable metabolic profile observed in metabolically healthy but obese and sarcopenic obese postmenopausal women. Further studies including metabolic data are needed to confirm our results.