GymAware RS vs FLEX

Not sure whether you should buy a GymAware RS or GymAware FLEX? Here’s the comparison you’re looking for. We dive into the hardware, software suite, pricing and look at the scientific validation and user reviews. Let’s get started.

By Loek Vossen

GymAware RS vs FLEX


GymAware RS

The GymAware RS uses a direct measurement technology. It works like a stopwatch and measuring tape, measuring time and distance. Together, these two measurements determine velocity.

The RS contains a spool and a tether. The tether works like a ruler/measuring tape, which you attach to the barbell or free weight. This system is called a Linear Position Transducer (LPT).

Unlike many other LPTs, GymAware RS considers the angle of the lift. This allows you to focus solely on vertical displacement, by correcting any horizontal movement. LPTs that don’t do this x-axis correction underestimate the movement distance.

Take for example a hang clean exercise. Many athletes put the barbell 3 feet (i.e.) behind the LPT device, so they don’t drop the bar on it. This creates a situation similar to the image below, with the LPT on the ground and the tether attached to the bar in the starting position (bar pos. A).

In the end position of your hang clean, the bar is in a new position (bar pos. B). You would like to know the displacement of the bar to calculate the speed (dashed orange line). However, an LPT measures the change in tether length of the tether in position A compared to the length of the tether in position B.

GymAware RS: Linear Position Transducer (LPT) with x-axis correction.

Without x-axis correction, you’re not measuring the displacement of the bar (orange dotted line). Instead, you measure the change in tether length of the tether in position A compared to the length of the tether in position B. This results in highly inaccurate velocity data. GymAware RS uses x-axis correction by considering the (orange) angle of the lift.

This change in tether length is significantly shorter than your bar displacement. As a result, your measurements are way off, getting lower velocity data.

There are two ways to solve this problem. You can make sure your bar goes up in a 100% vertical line and your LPT is placed straight underneath the bar (virtually impossible). The alternative is x-axis correction, by considering the angle of the lift. This is exactly what GymAware RS automatically does.

This makes GymAware RS a unique and incredibly versatile VBT device. Some example exercises you can use it for:

  • Barbell exercises
  • Pin loaded exercises
  • Kettlebell swings
  • Chin ups, jumps, dips, leg press, landmine press, nordic hamstring curls…
Learn more about GymAware RS

GymAware FLEX

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.

The FLEX unit is attached at the end of a barbell. The system requires a reflective mat underneath the laser to increase accuracy.

Velocity based training and mental health showcasing the GymAware FLEX

GymAware FLEX, attached to the end of a barbell, above a reflective mat.

GymAware FLEX can be used for all barbell exercises, including (barbell) jumps.

Comparison table: hardware

Scroll horizontally to see the full table on mobile devices.

GymAware RSGymAware FLEX
Measurement technologyLinear Position TransducerLaser optic technology
Required accessories-Reflective mat
Suitable forMultiple exercisesBarbell exercises
PricingUSD $1995USD $495

App & Cloud

Both VBT devices have their own app*. The FLEX Stronger app (iOS and Android) is for free and doesn’t require a subscription or monthly payment. The GymAware iPad app (iOS) has a free-run version too with additional paid subscription options.

*You can connect your FLEX unit with the GymAware iPad app and vice versa: you can connect your GymAware RS hardware with the FLEX Stronger app.

GymAware iPad app

The app for the GymAware RS is built for teams. It is the culmination of more than 20 years of industry experience and it is uniquely designed to meet the needs of coaches and other industry professionals.

You can unlock many advanced features by upgrading this app to the TEAMS app via an in-app purchase ($ 295 per year) in the free app. This allows for in-app leaderboards and many more.

The GymAware iPad app only runs on iOS (iPad only). For more information about the app, go to our app information page. There you will also find the link to download the app.

GymAware APP

GymAware iPad app

FLEX Stronger App – Android/iOS

The FLEX Stronger app is built for the needs of individual athletes, remote coaches and personal trainers. You can add other lifters into your session for group training with up to three people.

The FLEX Stronger app is available on iOS and Android.

1RM (repetition maximum) progress over time in the FLEX app for deadlift, bench press and back squat

FLEX Stronger app


If you want to take your training and coaching to a next level, GymAware Cloud is here to help. Note that this is optional, not necessary.

Both the GymAware RS and the GymAware FLEX can connect to the (same) GymAware cloud. 

The GymAware Cloud opens up a whole new set of opportunities. It allows you to gain full access to powerful reporting functions, training boards, cloud-based leaderboards and online analytics with a secure login via

With the GymAware Cloud Pro, you can connect seamlessly with Athlete Management Systems to integrate strength training data.

Learn more about the GymAware Cloud solutions via the button:

GymAware Cloud
GymAware hardware, app and cloud integration

Integration: hardware, app, cloud.

Comparison table: app & cloud

Scroll horizontally to see the full table on mobile devices.

FLEX Stronger appGymAware iPad appGymAware iPad app: teamsTeams app + cloudTeams app + cloud pro
PriceFREEFREE$295 /year$495 /year$995 /year
Velocity Based Training metrics
Real-time feedback
Velocity targets
Bar path
Rep level display
Video mode
Built-in 1RM test
Custom & pre-programmed workouts
In-app leaderboards
Cloud-based leaderboards24
Shows individual PB's
Multiple iPad synchronisation
Advanced velocity targets
Operating system appiOS and AndroidiOS (iPad only)iOS (iPad only)
Cloud access
Edit and Review Data
CSV exportMulti-day-Daily: data contains last 30 daysDailyMulti-day
Tailored reports
Mass add/import athletes
Athlete limit in one session3-250250500
Athlete limit for data storage-250250500
Coach logins--126
Data storedUnlimited-30 daysUnlimitedUnlimited
API connectivity to AMS
Athlete velocity profiling
Advanced VBT metrics
FLEX bridge
Contact product expert

Scientific validation

Accuracy and reliability are crucial in velocity based training. Here’s why inaccurate and unreliable VBT devices are useless at best and dangerous at worst.

There’s an almost never ending list of scientific publications showing the accuracy and reliability of GymAware RS. In fact, it is so accurate that scientists use it to validate other VBT sensors.

But how about the validation of the FLEX unit?

Validation FLEX vbt device

The GymAware linear position transducer (LPT) has been around for more than 20 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.

An independent scientific validation concludes 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: both the GymAware RS and the GymAware FLEX are highly accurate and reliable.


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.

Reviews FLEX vbt device

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

Joel Smith, founder of Just Fly Sports

“The device is lightweight, easy to set up, accurate, and futuristic-looking.”

Read the full FLEX review (June 2020).

Julian Chua, PhD in Sports Engineering

“I can tell that a lot of thought has been put into the design of the user interface and experience.”

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

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

More reviews:

“I was able to just train without the odd feeling of trying to work with a system – the system worked for me. The app is clean, responsive, and intuitive. I feel that it’s one of the better apps out there.”

Read the full FLEX review (December 2019).

Conclusion: should you buy GymAware RS or FLEX?

The GymAware RS and GymAware FLEX are both designed for Velocity-Based Training (VBT), but they cater to different user profiles and have some key differences.

GymAware RS has been the gold standard in VBT for more than 20 years. It offers the highest level of accuracy, which is crucial when the stakes are high. As a result, the GymAware RS is recommended for professional and elite-level athletes and coaches.

Compared to the FLEX unit, the GymAware RS can be used for a wide range of exercises beyond just barbell movements. Moreover, it does not require removal when changing weights.

GymAware FLEX has undergone independent scientific validation and is considered to be close to the gold standard in terms of accuracy. Additionally, it’s a more budget-friendly option. As a result, the GymAware FLEX is recommended for a wider range of users: individuals, high school athletes, personal trainers, etc. When combined with the GymAware iPad app and GymAware Cloud, it’s a good solution for teams as well.

Compared to GymAware RS, the GymAware FLEX is wireless, but it does rely on proper mat placement to ensure reps are not missed so it comes down to your preference of technology as well.

Still need some support in choosing your most suitable option? Contact our product expert! Ultimately, the key factors that should influence your decision of buying GymAware RS or FLEX are budget, technology preference, exercises you need to measure, type of users and the need for highest accuracy levels.


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