Muscle Quality Index as a Predictor of Functional Capacity in Cardiac Rehabilitation Patients

Background and Aims Muscle Quality Index (MQI), the ratio of handgrip strength to total skeletal muscle mass, is a potentially superior functional marker compared to mass or strength alone; its role in cardiac rehabilitation is under investigated in Indonesian populations. This research assess the association between MQI and the Six-Minute Walk Test (6MWT), and the diagnostic performance of MQI for severely reduced functional capacity (6MWT<240 m). Methods Cross-sectional study of 120 Phase 1 cardiac rehabilitation patients (85.0% male; mean age 59.7 years) at Prof. Dr. R.D. Kandou General Hospital. MQI was derived from handgrip-dynamometry and bioelectrical impedance analysis. MQI and 6MWT was done before discharge. Spearman correlation, multiple linear regression, Mann-Whitney U, and ROC curve analyses were performed. Results Median MQI was 1.39 (IQR 1.12–1.63); mean 6MWT was 318.3 m. Seven patients (5.8%) had 6MWT < 240 m. MQI was significantly lower in this group (median 0.93 vs 1.44; p=0.0004). MQI correlated positively with 6MWT (rs=0.197; p=0.031); quartile analysis showed a dose-response trend (Kruskal-Wallis H=12.62; p=0.006), with all severely reduced cases in Q1. Multivariable regression showed a clinically meaningful MQI contribution (B=23.84; p=0.091; R²adj=0.121; p=0.003). ROC analysis showed good discrimination (AUC=0.880), optimal cut-off MQI ≤ 1.20 (sensitivity 100%; specificity 69.9%). Conclusion MQI significantly correlated with functional capacity and demonstrated good discriminative ability (AUC = 0.880) for severely reduced functional capacity. An MQI threshold of ≤ 1.20 may serve as a practical screening cut-off in Indonesian cardiac rehabilitation.