Does a Validated Circum-menarcheal Arm Bone-Loading Index Predict Post-menarcheal Muscle Function in Adolescent...

In this exploratory analysis, we evaluated our validated 3-year circum-menarcheal arm bone loading index (ᴀʀᴍBLI) as a predictor of upper extremity muscle function indices in post-menarcheal females.

Forty-eight participants met inclusion criteria for non-dominant arm analyses, 1 to 2.5 years post-menarche: 1) menarche date (ɢʏɴAGE: yrs, menarche-centered age); 2) ᴀʀᴍBLI (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 (ᴀʀᴍNBꜰꜰᴍ, 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 (ɢʏɴAGE, height, weight, ᴀʀᴍBLI); 2) hypertrophy model (ɢʏɴAGE, ulna length, ᴀʀᴍNBꜰꜰᴍ, ᴀʀᴍBLI).

After accounting for key factors, ᴀʀᴍBLI 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, ᴀʀᴍBLI was an independent positive predictor of shoulder flexion peak torque in the total sample [whole-body model B= +0.270, p=0.036].

Despite prior work showing ᴀʀᴍBLI predicts ᴀʀᴍNBꜰꜰᴍ, ᴀʀᴍBLI showed inconsistent predictive value for muscle function indices.