Reliability and Accuracy of Linear Position Transducers During the Bench Press and Back Squat: Implications for Velocity-Based Training

Background: Selecting the right linear position transducer (LPT) for velocity-based training monitoring sometimes presents uncertainties for coaches. Objectives: This study rigorously examined the test-retest reliability of three LPT-Cs using a simultaneous triangulation method of the same device during bench press (BP) and back squat (SQ) exercises performed on a Smith machine. Methods: Forty university students-13 females (23 +/- 2 years) and 27 males (31.5 +/- 6 years)-voluntarily participated in a randomized repeated-measures study. LPTs were randomly assigned numbers and placed at 5 cm apart to measure and collect bar displacement (triangle S), mean propulsive velocity (MPV), peak velocity (PV), and time to peak velocity (T-PV). Each volunteer performed three BP and SQ attempts with pre-standardized loads (males: BP >= 40 kg and SQ >= 60 kg; females: BP >= 25 kg and SQ >= 40 kg). Results: The main findings of this study support a high degree of reliability for LPTs. For all variables, the absolute reliability presented significant values (p <= 0.05), with an intraclass correlation coefficient >= 0.995, a 95% confidence interval between 0.992-0.999, a coefficient of variation <= 10%, and a standard error of the mean <= 0.031. Conclusions: Scientists and coaches can use the LPT device as a reliable tool for monitoring velocity-based training by providing rigorous measurements of triangle S, MPV, PV, and T-PV during BP and SQ exercises. In addition, the smallest real difference reported may be useful in identifying minimal changes in triangle S within a single set (BP = 0.10 cm; SQ = 0.13 cm).