Criterion Validity, and Interunit and Between-Day Reliability of the FLEX for Measuring Barbell Velocity During Commonly Used Resistance Training Exercises

Abstract

Weakley, J, Chalkley, D, Johnston, R, García-Ramos, A, Townshend, A, Dorrell, H, Pearson, M, Morrison, M, and Cole, M. Criterion validity, and interunit and between-day reliability of the FLEX for measuring barbell velocity during commonly used resistance training exercises. J Strength Cond Res 34(6): 1519–1524, 2020—The aim of this study was to assess the criterion validity, interunit reliability (accounting for technological and biological variance), and between-day reliability of a novel optic laser device (FLEX) for quantifying mean concentric velocity. To assess the validity against a three-dimensional motion capture system and interunit reliability with both technological and biological variation, 18 men and women completed repetitions at 20, 40, 60, 80, 90, and 100% of one repetition maximum in the free-weight barbell back squat and bench press. To assess interunit (technological only) reliability, a purpose-built, calibrated rig completed a set protocol with 2 devices. To assess between-day reliability of the technology, the same protocol was repeated 21 days later. Standardized bias, typical error of the estimate (TEE; %), and Pearson's correlation coefficient (r) were used to assess validity, whereas typical error and coefficient of variation (CV%) were calculated for reliability. Overall, TEE (±90 CL) between the FLEX and criterion measure was 0.03 (±0.004) and 0.04 (±0.005) m·s−1 in the back squat and bench press, respectively. For measures of reliability, overall interunit technological variance (CV% [± 90% confidence interval]) was 3.96% (3.83–4.12) but increased to 9.82% (9.31–10.41) and 9.83% (9.17–10.61) in the back squat and bench press, respectively, when biological variance was introduced. Finally, the overall between-day reliability was 3.77% (3.63–3.91). These findings demonstrate that the FLEX provides valid and reliable mean concentric velocity outputs across a range of velocities. Thus, practitioners can confidently implement this device for the monitoring and prescription of resistance training loads.

The Validity and Reliability of Commercially Available Resistance Training Monitoring Devices: A Systematic Review

“…Devices were deemed to have demonstrated 'acceptable' validity if the literature reported a very high correlation ([ 0.70), moderate CV (\ 10%), and a trivial or small ES (\ 0.60) based on a modified effect size scale [45]. This is consistent with previous resistance training literature which has assessed the validity of resistance training devices [8,22,46]. Devices were said to demonstrate acceptable reliability if a device had an intra-class correlation coefficient C 0.90, CV \ 10%, and a standardised mean bias \ 0.60.…”

“…It should be noted that LPTs should not be confused with linear velocity transducers (LVTs), which determine kinetic and kinematic outputs through the direct measurement of instantaneous velocity. Furthermore, in recent times, there have been a range of new devices that monitor resistance training outputs, with these being made possible through advancements in technology [22]. Examples of these include optic laser devices and the cameras within smartphones [22,23].…”

“…Furthermore, in recent times, there have been a range of new devices that monitor resistance training outputs, with these being made possible through advancements in technology [22]. Examples of these include optic laser devices and the cameras within smartphones [22,23]. While validity and reliability data have been published on these new devices, they have sparingly been compared to linear transducer (i.e., either LPTs or LVTs) and accelerometer data [24].…”

“…Intra-device reliability is essential to consider when tracking and identifying 'meaningful' changes over a specified period [34]. However, when assessing the reliability of an instrument, it is important to separate biological (i.e., human) and technological variation [22]. This is particularly pertinent during resistance training, where fluctuations in strength and readiness to train can cause substantial alterations in velocity and power outputs despite the same relative load being used [31,35].…”

The reliability of a linear position transducer and commercially available accelerometer to measure punching velocity in junior boxing athletes

“…Future research should consequently look to expand upon these results and use similar statistical approaches to account for device error and establish if the PUSH Band 2.0 and GymAware are valid when compared with either three-dimension motion capture 11,27 or optic laser. 32…”