Objective: In this exploratory analysis, we evaluated our validated 3-year circum-menarcheal arm bone loading index (ARMBLI) as a predictor of upper extremity muscle function indices in post-menarcheal females. Methods: Forty-eight participants met inclusion criteria for non-dominant arm analyses, 1 to 2.5 years post-menarche: 1) menarche date (GYNAGE: yrs, menarche-centered age); 2) ARMBLI (3-yrs prior loading exposure); 2) grip strength (kg; primary outcome), 3) Biodex peak torques (Nm: shoulder, elbow; flexion, extension; secondary outcomes), 4) DXA arm non-bone fat-free mass (armNBffm, kg), 5) anthropometry [ulna length (mm), height (cm), weight (kg)]. Multiple linear regression evaluated muscle function in the total sample (n=48), gymnasts (n=24), and non-gymnasts (n=24), accounting for key factors: 1) whole-body model (GYNAGE, height, weight, ARMBLI); 2) hypertrophy model (GYNAGE, ulna length, ARMBFFM, ARMBLI). Results: After accounting for key factors, ARMBLI was an independent negative predictor of grip strength in the total sample [hypertrophy model B= -0.202, p=0.029] and non-gymnast subsample [hypertrophy model B= -0.935, p=0.030; whole-body model B= -1.127, p=0.005]. Conversely, ARMBLI was an independent positive predictor of shoulder flexion peak torque in the total sample [whole-body model B= +0.270, p=0.036]. Conclusions: Despite prior work showing ARMBLI predicts ARMNBFFM, ARMBLI showed inconsistent predictive value for muscle function indices.