The Coaches’ Eye: A Randomized Repeated-Measure Observational Study Assessing Coaches’ Perception of Velocity Loss during Resistance Training Exercises.

Background: Resistance training (RT) coaches regularly instruct their trainees to terminate a set based on their estimation that repetition velocity has dropped beyond a certain threshold, aligning with the concept of velocity loss in the velocity-based training (VBT) method. However, this ability has never been studied. Here, we assess the accuracy of RT coaches in estimating the repetition velocity loss of trainees. Methods: Twenty RT coaches participated in a single experimental session in which they observed videos of two trainees completing sets of the barbell bench press and barbell back squat exercises, using three loads (45%, 65%, and 85% of 1 repetition-maximum [1RM]), and recorded from two views (front and side). We asked them to estimate when repetitions exceeded two velocity loss thresholds (20% and 40%). We examined whether velocity loss threshold, load, view, mental fatigue, and gaze strategy influenced estimation accuracy. We compared outcomes using a negative binomial generalized mixed-effects model. Results: The average absolute accuracy error across all conditions was 2.6 repetitions, with errors ranging from 1 to 5 repetitions. Coaches improved their accuracy (negative estimates indicate reduced error) when estimating higher velocity loss threshold (40% vs 20%; −1.8, 95%CI [−2.3, −1.3]), using heavier loads (−0.8, 95%CI [−1.5, −0.1]) for 65% 1RM, and −3, 95%CI [−3.4, −2.6] for 85% 1RM compared to 45% 1RM), and employing a bar tracking gaze strategy compared to a no-bar strategy (−1.7, 95%CI [−2.7, −0.4]). These findings were consistent across both points of view, with mental fatigue having a negligible impact. Conclusions: While coaches perceive velocity loss with some degree of accuracy, their error rates vary depending on the velocity loss threshold, load, and gaze strategy used. Coaches should consider these error rates with their specific RT goals when using perceived velocity loss in practice.