The Coach’s 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 when the repetition velocity drops below a certain threshold, aligned with the principles of velocity loss in velocity-based training (VBT). However, absent of a velocity-tracking device, coaches are required to detect velocity loss through observation-a topic that has never been studied. Here, we assess the accuracy of RT coaches in detecting when trainees reach specific repetition velocity loss thresholds. METHODS: Twenty RT coaches participated in a single experimental session. 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 detect when repetition velocity dropped below two velocity loss thresholds (20% and 40% relative to their first repetition). We examined whether load, velocity loss threshold, view, mental fatigue, and gaze strategy (bar or no-bar tracking) influenced accuracy. We compared outcomes using a negative binomial generalized mixed-effects model. RESULTS: The average absolute error across all conditions was 2.6 repetitions. Coaches improved their accuracy (negative estimates indicate reduced error) when observing a higher velocity loss threshold (40% vs 20%; - 1.8, 95%CI - 2.3, - 1.3); observing 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). In contrast, point of view and mental fatigue had a negligible effect. CONCLUSIONS: While coaches detect velocity loss with some degree of accuracy, their error rates vary depending on the threshold, load, and gaze strategy. These factors should be considered when using perceived velocity loss in practice.