# From Physiology to Practice: Validation of Eccentric Velocity Monitoring Using an Optoelectronic System

## TL;DR

The PowerTrackTM device accurately and reliably measures eccentric velocity during squats, making it useful for training applications.

## Contribution

The study validates PowerTrackTM as a field-ready tool for eccentric velocity monitoring in multi-joint exercises.

## Key findings

- PowerTrackTM showed very high validity for eccentric peak velocity during the Smith machine back squat.
- Inter-session reliability of eccentric velocity outcomes was excellent, supporting practical use in training.
- Eccentric peak velocity (Vmax) is a more robust metric than mean velocity for monitoring eccentric actions.

## Abstract

What are the main findings?
PowerTrackTM showed very high validity for eccentric phase velocity during the Smith machine back squat when compared with the criterion system (MuscleLabTM), particularly for eccentric peak velocity.Inter-session reliability was excellent for eccentric velocity outcomes, supporting the device’s practical use for eccentric velocity-based training in applied settings.

PowerTrackTM showed very high validity for eccentric phase velocity during the Smith machine back squat when compared with the criterion system (MuscleLabTM), particularly for eccentric peak velocity.

Inter-session reliability was excellent for eccentric velocity outcomes, supporting the device’s practical use for eccentric velocity-based training in applied settings.

What are the implications of the main findings?
Eccentric–phase velocity during the Smith machine squat can be monitored with high validity and reliability using an PowerTrackTM optoelectronic sensor.Eccentric peak velocity (Vmax) appears to be a more robust metric than eccentric mean velocity (MV) for monitoring eccentric actions in multi–joint resistance exercises.

Eccentric–phase velocity during the Smith machine squat can be monitored with high validity and reliability using an PowerTrackTM optoelectronic sensor.

Eccentric peak velocity (Vmax) appears to be a more robust metric than eccentric mean velocity (MV) for monitoring eccentric actions in multi–joint resistance exercises.

Background: Accurate monitoring of eccentric phase velocity is needed to support velocity-based training (VBT), yet field-valid tools for multi-joint exercises are scarce. This study evaluated the concurrent validity and reliability of an optoelectronic device to quantify eccentric phase velocity during the Smith machine back squat. Methods: A total of 20 resistance-trained men completed two sessions and performed three repetitions at three submaximal loads (20, 50, and 70 kg). Eccentric mean velocity and peak velocity (Vmax) were recorded simultaneously using PowerTrackTM and a criterion system (MuscleLabTM). Validity was assessed using ordinary least products regression, Lin’s concordance correlation coefficient (CCC), and Bland–Altam analysis. Reliability was examined via intraclass correlation coefficients (ICC), standard error of measurement (SEM), coefficient of variation, and minimum detectable change. Results: Agreement between devices was very high for Vmax (slope ≈ 1.00; CCC = 0.95), with a small constant bias. Eccentric mean velocity showed proportional bias under higher velocity conditions, whereas overall concordance remained high (CCC = 0.95). Inter-session reliability was excellent (ICC = 0.87–0.96), with low SEM values for eccentric velocity metrics. Conclusions: PowerTrackTM can be a valid and reliable tool for monitoring eccentric phase velocity during the Smith machine back squat, with Vmax representing the most robust metric for applied eccentric VBT.