The coaches' eye: a randomized repeated-measure observational study assessing coaches' perception of velocity loss during resistance training exercises.

Prescribing resistance training (RT) involves programming various training variables, including exercises, loads, sets, repetitions, and rest intervals (Coratella, 2022). Over the years, numerous fixed and predetermined RT programs have been developed, providing coaches with general recommendations tailored to specific populations and outcomes (Fragala et al., 2019). For example, a RT program designed to improve muscular strength in novice and intermediate trainees includes 1–3 sets of 8–12 repetitions at 70–85% of one repetition maximum (1RM) (Nuzzo et al., 2023). Importantly, fixed and predetermined RT programs typically rely on a single baseline performance measure (e.g., 1RM) taken at the start of a training cycle. While such fixed and predetermined approaches are practical at the group level (Fragala et al., 2019), they lack individualization by failing to account for between- and within-trainee day-to-day performance variability. Several factors, including fatigue (Shimano et al., 2006), sleep deprivation (Knowles et al., 2018), inadequate diet (Judelson et al., 2007), and short-term training adaptations, lead to such variability. Accordingly, fixed and predetermined RT programs do not allow for the frequent adjustments needed to account for consistent performance fluctuations, often resulting in overloading on some days and underloading on others (Judelson et al., 2007).In RT, coaches often rely on their judgment to determine when a trainee should stop a set based on their perception in change of velocity, in line with the velocity-based training (VBT) method. However, how the coach perceives changes in velocity loss, has not been thoroughly studied. In this study, we aimed to evaluate the accuracy of RT coaches in estimating trainees' repetition velocity loss.Twenty RT coaches participated in a single experimental session and watched a series of twenty-four video clips of two trainees (male and female), performing sets of barbell bench press and barbell back squat exercises at three different loads (45%, 65%, and 85% of 1RM) from two perspectives (front and side). They were asked to estimate when the trainees reached two velocity loss thresholds (20% and 40%) relative to the first repetition in each set. This study investigated 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.Across all conditions, the average absolute accuracy error was 2.6 repetitions, with individual errors ranging from 1 to 5 repetitions. Coaches showed improved accuracy when estimating a 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 when 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 perspectives, with mental fatigue having a minimal impact.While coaches can perceive velocity loss with a certain degree of accuracy, their error rates vary depending on the velocity loss threshold, load, and gaze strategy used. Coaches should take these error rates into consideration when applying perceived velocity loss in their training practices.