DEFINING SARCOPENIA USING MUSCLE QUALITY INDEX

Objectives: Although low muscle quality is a strong predictor of sarcopenia, defining sarcopenia using muscle quality remains unknown. This study investigated the cut-points to define sarcopenia using muscle quality index (MQI) in the young reference population. Methods: Fifty healthy young (20 to 29 years) and forty elderly adults (60 to 79 years) were recruited in this study. Dual-energy X-ray absorptiometry was used to assess appendicular skeletal muscle mass. Hand grip and leg dynamometers were used to measure muscle strengths in the arm and leg. Muscle quality in the arm (MQIArm, kg/kg) and leg (MQILeg, Nm/kg) were computed as muscle strength per lean mass in the arm and leg, respectively. Total muscle quality (MQITotal) was computed as the combination of MQIArm and MQILeg, while standardized muscle quality (MQIStd) was computed as the combination of z-scores in MQIArm and MQILeg. Sarcopenia was defined as ≤2 SD below from the mean values in the young reference group. Results: The cut-points for defining sarcopenia using MQIArm, MQILeg, MQITotal, and MQIStd in men were ≤8.37, ≤12.07, 22.06, and <-3.35, and in women were ≤10.09, ≤13.97, 28.22, and <-2.25, respectively. In the elderly adults, the frequencies of sarcopenia using MQIArm, MQILeg, MQITotal, and MQIStd were 15%, 27.5%, 32.5%, and 35%, respectively. Conclusion: This study establishes new values for defining sarcopenia using MQIs. The proposed new MQI cut-points may be a role in detecting sarcopenia across individual and population level.