There’s an almost never ending list of scientific publications showing the accuracy and reliability of GymAware RS. But how about the validation of the FLEX unit? Discover the independent validation studies and user reviews of the FLEX bar tracker for VBT.

You might also be interested in the FLEX product page or GymAware RS validation page or GymAware RS vs FLEX comparison page.

An inaccurate (not valid) and unreliable VBT device is useless at best and dangerous at worst. While you think you’re making informed decisions, those decisions are actually based on wrong data.

Although the importance of accuracy and reliability may sound like a no brainer, not all VBT devices meet these criteria.

Learn more about the importance of accuracy and reliability.

The FLEX device uses laser optic technology that measures vertical and horizontal bar position relative to the ground. By differentiating this position data you get highly accurate velocity measures. It’s an inexpensive way of bringing VBT to life in your gym, garage, high school or elite setting.

The VBT sensor fits on the end of a barbell like a collar. The laser reflects on a mat underneath the bar.

The GymAware linear position transducer (LPT) has been around for over 22 years. The knowledge and experience helped us to create the world’s first and only laser based VBT device – FLEX. Science shows that this was done successfully.

The first independent validation study on FLEX was published in 2020. This study has it all – a few thousand repetitions worth of data, high speed motion capture, free weight exercises, and it’s the first VBT device validation study that was able to distinguish between technological and biological error.

The research team – led by Dr Jonathon Weakley – put FLEX through its paces and concluded 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.”

To be a bit more specific: the typical error of the FLEX was 0.03 m/s in the back squat and 0.04 m/s in the bench press. This was measured in a wide range of loads (20-90% 1RM) and therefore a wide range of velocities (1.09 – 0.30 m/s).

When you put two FLEX units on a barbell, the inter unit variance was less than 4%. Between-day variability turned out to be very low too (<4%).

In other words: the FLEX  unit is highly accurate and reliable.

Scientists agree on the value of the FLEX unit, but how about coaches and practitioners in the field?

Discover countless authentic user videos on the GymAware instagram feed or FLEX instagram feed and have a look at the tagged section as well.

At the time of writing, Trustpilot shows a rating of 4.6 stars (out of 5), based on 28 GymAware FLEX reviews. This gives it the Trustpilot status of Excellent.

GymAware FLEX Trustpilot reviews

Scientists agree on the value of the FLEX unit, but how about coaches and practitioners in the field?

Discover countless authentic user videos on the GymAware instagram feed or FLEX instagram feed and have a look at the tagged section as well. Rather dive into some in-depth review articles? We listed some below.

Note that we listened to their feedback and therefore implemented most of their suggestions already. For example:

• Embedded camera recording within the FLEX Stronger app
• Eccentric metrics
• Exercise assist
• App on iOS and Android

Read the full FLEX review (June 2020).

Read the full FLEX review, part I (March 2020).

Read the full FLEX review, part II (June 2020).

Read the full FLEX review (December 2019).

Now that you know how scientists and coaches in the field think about FLEX, it’s time to experience it yourself! Learn more about the FLEX hardware and software, or ask your questions to our product expert.

We now finish with a (non complete) FLEX literature list.

“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.”

• Weakley, J., Chalkley, D., Johnston, R., García-Ramos, A., Townshend, A., Dorrell, H., Pearson, M., Morrison, M., & Cole, M. (2020). Criterion Validity, and Interunit and Between-Day Reliability of the FLEX for Measuring Barbell Velocity During Commonly Used Resistance Training Exercises. Journal of strength and conditioning research, 34(6), 1519–1524.

“The optic laser Flex device has demonstrated acceptable validity for mean velocity during both free-weight squat and bench-press exercises across a range of loads. (…) the typical error is approximately 0.02 m·s−1.”

• Weakley J, Morrison M, García-Ramos A, Johnston R, James L, Cole MH. The Validity and Reliability of Commercially Available Resistance Training Monitoring Devices: A Systematic Review. Sports Med. 2021 Mar;51(3):443-502.