PREDICTIVE VALIDITY OF LOAD-VELOCITY MODELS TO DETERMINE THE ONE-REPETITION MAXIMUM IN TRAINED POWERLIFTERS

INTRODUCTION
Over the past years, various concepts have been suggested to estimate a person’s one-repetition maximum (1-RM) for a given resistance training exercise based on the load-velocity or force-velocity relationship (Hughes et al., 2018). However, the predictive accuracy of such models has not been affirmed consistently in research, as they may be affected by various methodological aspects (Picerno, 2017). The present investigation was conducted to analyze different load-velocity model configurations on their validity to assess the individual 1-RM in a sample of highly strength-trained athletes.
METHODS
Twenty-four trained powerlifters (18 male and 6 female; age: 25.1±5.1 y; body mass: 90.9±20.0 kg) completed a strength test in the back squat exercise at maximum voluntary concentric velocity. Progressive load increments were chosen until participants reached their true 1-RM (relative 1-RM: 1.96±0.25 kg.kg-1). Simultaneously, vertical movement velocity of the barbell was assessed using 3D motion capturing (Vicon-460). Based on individual load-velocity data, eighteen model configurations were selected to estimate the 1-RM. The models differed in predictive approach, regression characteristics and applied velocity variable. Validity of the model estimates and moderator effects of 1-RM strength performance on estimation error were analyzed using magnitude-based inferences at a 90% confidence level.
RESULTS
Models using mean velocity or mean propulsive velocity as predictor variable while calculating the 1-RM from a minimal velocity threshold (MVT) demonstrated a very likely to most likely substantial overestimation of the true 1-RM (mean estimation error: 7.4 to 11.3%). All other models resulted in unclear trends. Moderator analysis revealed a positive, most likely substantial modifying effect of 1-RM strength performance on absolute estimation error in linear models computed from 2 or 5 data pairs using mean velocity as predictor variable [Δ2*SD (90% CL): 19.5 kg (6.6, 32.4) and 16.0 kg (2.6, 29.4), respectively].
DISCUSSION
The present findings corroborate the hypothesis that MVT-based 1-RM calculations using mean velocity or mean propulsive velocity as predictor variable lead to systematic overestimation of the true 1-RM in the back squat exercise (Banyard et al., 2017). In particular, stronger athletes appear to experience higher absolute overestimation of their performance compared to weaker athletes when applying these model configurations.

Banyard, HG et al. (2017) J Strength Cond Res. 31(7), 1897–1904.
Hughes, LJ et al. (2018) J Strength Cond Res. [Epub ahead of print].
Picerno, P (2017) Asian J Sports Med. 8(3), 1-7.