Association between muscle quality index and time to stand up from the prone position in community-dwelling older adults

Both muscle strength and muscle quality are essential factors for preserving autonomy and functionality in older adults (OA). However, the relationship between muscle quality index (MQI) and the time to stand up from the prone position (SPP) in this population is unknown. The primary purpose of this study was to determine the relationship between MQI and SPP completion time in community-dwelling OA capable of performing the test, considering age, sex, stature, and fat mass percentage. This cross-sectional study included 376 OA (70.47 ± 6.95 years; 234 women and 142 men). Functional Autonomy (FA) was assessed using the GDLAM protocol, and MQI was calculated as manual grip strength divided by body mass index (N/BMI). Pearson's test was used to correlate parametric data, while Spearman's was used for non-parametric data. For both the dominant (D) and non-dominant (N-D) limbs, the analysis showed a high correlation between MQI and time in the SPP test (D: r = −0.55, 95% CI −0.62 to −0.48, p < 0.0001; N-D: r = −0.57, 95% CI −0.64 to −0.50, p < 0.0001). This association remained significant in all four regression models after adjustment (all p < 0.001), with models based on body mass showing greater explanatory power than those based on body mass index (adjusted R² 0.351–0.366 vs. 0.343–0.360). These results indicate that higher MQI is associated with shorter SPP completion time in community-dwelling OA. Therefore, the SPP test shows potential as a practical, field-based indicator associated with FA in this population.