Reliability and Validity of the Load-Velocity Relationship for Predicting the 1 RM in the Bulgarian Split Squat Exercise
(Hao Yan, Haiting Zhai, Tingting Wang, Duchun Wang, Hongwen Wei)

This study aimed to compare the reliability and validity of various prediction models based on load-velocity relationships for predicting the one-repetition maximum (1 RM) in Bulgarian split squat (BSS) exercises. Twenty-seven resistance-trained men participated in the study, completing both a 1-RM test and a progressive loading test to determine the 1 RM value, along with the mean velocity (MV) and peak velocity (PV) for each load. Load-velocity relationships were constructed using linear and binomial regression equations. The results revealed a strong correlation between different velocities and relative loads in BSS exercises (R² = 0.880–0.964), with the MV-based model slightly outperforming the PV-based model (R² difference of 0.06 and SEE difference of 0.02). Additionally, both MV and PV across all test loads demonstrated good reliability (ICC ≥ 0.801; CV ≤ 2.36%). Despite very strong correlations between the actual and predicted 1 RM across all models (R = 0.890–0.972), linear regression models and binomial regression models for the dominant leg consistently underestimated the actual 1 RM (p ≤ 0.035). Only the binomial regression models for the non-dominant leg accurately predicted the 1 RM (p ≥ 0.223). In conclusion, modeling using MV and binomial regression provides more reliable and accurate 1 RM predictions for BSS exercises. These findings confirm the utility of load-velocity relationships in predicting 1 RM for BSS exercises and suggest that practitioners should use MV and polynomial regression equations for predicting 1 RM in highly complex free-weight resistance exercises.