Objectives: Vosoritide, a C-type natriuretic peptide analog, is the first approved pharmacological treatment for achondroplasia that targets the overactive FGFR3 pathway and promotes longitudinal bone growth. As increased body height may improve biomechanical leverage and influence muscle function, this retrospective, monocentric, observational study aimed to evaluate changes in muscle performance parameters during long-term vosoritide treatment. Methods: Nineteen (19) children with achondroplasia treated with vosoritide for at least 12 months were included. Muscle function was assessed via two-legged jump tests on a ground reaction force plate at baseline, month 12, 24 and 36. Jumping parameters, 6-minute walking distances and auxological measurements were converted to z-scores. Longitudinal changes were detected using a linear mixed-effects model. Results: Vosoritide treatment resulted in significant gains in height z-scores over 36 months (p < 0.001). Raw values of jumping parameters increased numerically over time for all parameters except relative force; however, no significant changes were observed in z-scores. Similarly, no significant changes were detected in 6-minute walking distances. Conclusions: While vosoritide produced significant height gains, no significant changes in muscle function z-scores were observed in this cohort. These findings are exploratory and suggest that muscle function may develop in parallel with that of unaffected children.