Development and validation of prediction models for one-repetition maximum based on bioelectrical impedance analysis in adults of all ages

[Purpose] This study aimed to develop and internally validate one-repetition maximum prediction models based on skeletal muscle mass or skeletal muscle mass index measured using bioelectrical impedance analysis in adults across all ages and both sexes. [Participants and Methods] Eighty-two participants (40 males, 42 females, aged 20-84 years) completed measurement of dominant leg skeletal muscle mass and skeletal muscle mass index using multifrequency bioelectrical impedance analysis. Unilateral leg press one-repetition maximum was measured. Two multiple linear regressions that incorporated age and sex were fitted and internally validated through bootstrap resampling. [Results] The model using skeletal muscle mass produced an adjusted R² of 0.701 and a standard error of estimate of 16.01 kg. The model using skeletal muscle mass index demonstrated higher accuracy (adjusted R²=0.737; standard error of estimate=15.0 kg). Internal validation indicated minimal overfitting, with optimism-corrected adjusted R² values of 0.677 and 0.715 and standard error of estimate values of 16.82 and 15.81 kg, respectively. [Conclusion] The developed and internally validated models can reasonably predict unilateral leg press one-repetition maximum in adults across a broad age range. However, caution is warranted owing to the magnitude of the prediction error.