Background Inflammatory states, hypovitaminosis D and secondary hyperparathyroidism may have a role in the age-related loss of muscle mass, and physical performance in healthy old people. The aim of this study is to investigate changes in muscle mass, strength and physical performance in healthy, active elderly females over a 3-year follow-up, correlating them with any inflammatory states and PTH and 25-hydroxyvitamin D (25-OHD) levels. Methods One hundred healthy females over 65years of age routinely attending a twice-weekly mild fitness program were eligible for the study. Clinical history, serum parameters, body composition by DEXA, handgrip strength, knee extensor isometric/isotonic strength and functional performance measured using the Short Physical Performance Battery (SPPB) were evaluated at the baseline and after 3years. Results After 3years, the women had a significant decrease in weight (∆:−0.8±3.1kg; p<0.05) and height (∆:−0.4±0,6cm; p<0.001), while their BMI and body composition parameters did not change. Only IL-6 (∆: 0.6±2.0; p<0.01) and PTH (∆: 30.7±29.2ng/L; p<0.001) increased significantly, while there were no changes in 25-OHD levels. There was a significant decrease in all the SPPB results and in muscle strength. ∆ PTH only correlated with the variation in 4-meter walking speed (r: 0.41; p<0.01). Conclusions With advancing age, physical performance declines even in healthy, active females despite a spare of muscle mass. The increase in PTH seems to have a role in this decline, that could be clarified by further investigations.