A Rapid Review of the FLEX Barbell Tracker

One of the new disruptions in sports training comes from a familiar name in velocity-based training: Kinetic Performance, the makers of GymAware. Their new product, FLEX, is a different animal, and because technology can be confusing at times, I wanted to put out a review as soon as possible. What I thought would be a quick evaluation became a few months of really looking at the technology and comparing it to the current competition, as well as the GymAware team solution.

If you wonder whether the system is a good fit for you and/or your athletes, this article tells you everything you ought to know about the product. I will not cover anything methodology-wise, give tips on better training, or even speculate on what its future will be. Today, you can pick up a FLEX system for about $500, and it’s worth the price. I recommend it for remote coaching and private clients.

If you want a personal device, a travel solution for a few athletes, or a way to get started with barbell tracking, I suggest picking up the FLEX, says @spikesonly. Click To Tweet

It’s not an enterprise solution, so if you work with teams and want to find a more frugal approach to managing the weight room, this won’t be right for you. But if you want a personal device, a travel solution for a few athletes, or a way to get started with barbell tracking, I suggest picking one up.

Comparing the FLEX and GymAware Systems

Before we get into the FLEX product, I need to say upfront that the FLEX and GymAware systems use completely different technology strategies to measure barbell motion. A lot of coaches assume that price and accuracy go hand-in-hand, but the truth is that engineering is about knowing what you can do and knowing the limitations of measurement. I have used barbell tracking for more than 20 years, and I really started to get interested in the technology when the iPhone liberated the GymAware system 10 years ago. The company, Kinetic Performance, has provided a monitoring solution as well as the GymAware for elite teams for more than a decade.

The GymAware is a linear encoder with horizontal measuring, which means it’s not a pretty TENDO Unit. Other systems have surfaced in the meantime, such as Speed4Lifts and RepOne, but GymAware is not just hardware and an app; it’s a testing solution as well. Linear encoders are seen as more primitive because the bar connects to a thin line or wire, but this isn’t really a big deal. The few proponents of “wireless” barbell tracking and vocal critics of linear encoders are the same people that either sell chains and bands hooked to barbells or post Pallof presses with cables on Instagram constantly. You can’t have it both ways.

FLEX is obviously different. The entire sensor is on the end of the bar versus connected to the bar itself. The system is technically wireless, but the sensor requires a reflective surface to work properly. I talk about the included mat in detail later, but for the most part, the system does improve the user experience a bit with the actual training. I like linear encoders, as it feels like you are challenging the system, and video-based solutions or motion capture experiences sometimes feel a little synthetic. An obvious difference is that FLEX is a smartphone solution, so it’s more of a portable experience than something enterprise-oriented or permanent.

The last point is that both systems connect to the cloud and allow you to see the data later. This is important because coaches want a nearly turnkey solution for training. You can use online strength and conditioning software during training with FLEX, but it requires going back and forth a bit. This is fine for athletes who train privately or on their own, so if you work remotely with clients, it’s not an issue. FLEX can work with TeamBuildr, Bridge Athletic, CoachMePlus, and AthleteMonitoring (testing for now) via the GymAware bridging software and API.

How the FLEX System Works

If you don’t care about how a sports technology system works, it’s likely you will be completely dependent on others to help you make decisions. To me, that is dangerous. I don’t like black boxes or misleading marketing from sports technology companies.

The FLEX device is basically a bike wheel, but instead of internal spokes, it has a “strip of lights” used to see both distance and orientation with high precision. The optical sensor measures the change of bar displacement vertically and horizontally (small changes), so it can trace the repetition of the lift at 50 hertz.

While the sampling rate isn’t exciting, one advantage is that barbell lifts are, for the most part, not fast like sprints or jumps. They are usually.5–2.5 m/s at peak. For the majority of exercises, a lower sampling rate is fine, but I would have preferred for it to be faster to get the early rate of force, if possible. Still, most coaches want to see how the bar moves in time and space with conventional exercises, so this is perfectly fine.

If you have a barbell with undersized ends or that isn’t especially magnetic, the FLEX also has a built-in locking ring that users can tighten, says @spikesonly. Click To Tweet

Features outside of the sensor are small nuances, like a well-designed magnet to keep the sensor on the bar. There is a rumor that dropping the barbell will cause damage or cause the sensor to pop out. I don’t think this is happening with any of the primary exercises because of both the depth of the barbell cup and the magnet being so locked in. If you have a barbell with undersized ends or that is not especially magnetic, the FLEX also has a built-in locking ring. Users can tighten this down, so that an O-ring compresses around the barbell. This ensures that FLEX attaches securely to the barbell.

Video 1. The FLEX device leverages light sensors to detect the change in distance from the ground in multiple angles, not just vertically. Using the array of light sensors enables full barbell tracking, not just the speed of the movement.

Anything is possible, but I don’t think anyone will have a problem. Do keep in mind that the device hasn’t been around for years. Kinetic Performance has spent a lot of time developing the product, however, so I am sure it’s designed to hold up, and after 1,000 reps, it has yet to fail.

The next few features are obvious and common components of a modern sports device. FLEX uses Bluetooth for wireless transmission of the sensor data to the application, and the system charges with a typical micro USB cable. The app data is cleaned and calculated so the speed and bar path are recorded and, of course, displayed on the iPhone within a fraction of a second. If the phone is connected to Wi-Fi or cellular, it synchronizes to the FLEX cloud for saving and backup. GymAware users can transfer and store data straight into their GymAware Cloud account.

FLEX has its strengths and limitations, but when you measure performance, you need valid and trustworthy devices. Companies often compromise on accuracy and precision, and they accept this when it means higher profits, but this needs to stop. My overarching point is simple: If you want good data, you need to buy the right stuff.

The Barbell Tracking Tool in Action

Sometimes a video doesn’t paint a complete picture, so I will go into details that really determine the design elements and adoption rate. When observing the product in action, I saw a few areas that really impressed me. However, I also realized that no matter how great the technology, barbell tracking is hard to implement in the wild. I have done motion capture in the past, and it produced useful research information for us, but it wasn’t going to be replicated in a market where a normal gym can get value. Also, the more practical a product, the more likely there is a catch with limitations on what it can measure and how good the numbers are.

Without getting nasty, you must both look at the most available research and do internal testing to evaluate the data. The FLEX product has a few advantages over many of the accelerometer products that don’t interfere with user experience. Not all accelerometer products are the same, I know, but the difference between Kinetic Performance and most of the market is that their product measures the rep as is, rather than trying to estimate what the bar may be doing. Rep detection is everything, and intelligence is not just an algorithm or calculation—it’s selecting a process that gives the user confidence that the measurement is valid.

The difference between Kinetic Performance and most of the market is that their product measures the rep as is, rather than trying to estimate what the bar may be doing, says @spikesonly. Click To Tweet

Let’s start with placement of the sensor at the end of the barbell, similar to the FORM lifting collar years ago. Yes, bar whip could, in theory, change the values slightly, but it’s unlikely to be an issue unless you change bars with dramatically different stiffness properties. Coaches want a reliable number that means something, so while some accuracy is lost, it’s not a big deal because the difference isn’t as meaningful as we thought. Practically, you will have to take the cap off and put it on, but the magnet is excellent so that isn’t worth worrying about.

When you change the weight plates, it’s not really an issue as you’re already interacting with the barbell. The bonus is that when you place FLEX back onto the barbell, the app automatically prompts you to enter the new barbell weight. I do have a custom markerless motion capture system that is very expensive and uses multiple vantage points, but a cap on the end of the bar is not a deal breaker.

The reflective mat is something you will have to deal with. True, it’s not ideal, but again, I would rather have a tiny inconvenience and quality data than a random number generator with cool logos and free T-shirts handed to me at conferences. The portability of the mat isn’t bad, but it’s not great for those wanting the most portable. It’s small enough for a backpack or carry-on, though. The mat can take a beating, as I have dropped a few cleans on it, so don’t worry that it will break down. In any case, the mats are replaceable.

As I stated earlier, you can elect to use reflective paint, but I don’t know the durability of that option. It shouldn’t be that high maintenance, since, technically, the space from where it reads shouldn’t be a high wear-and-tear area. Longer term, there should be 3-foot by 3-foot rubber floor tiles with built-in reflective properties so users can switch out their existing tiles and add in new ones.

Now comes the app itself. I feel that it’s one of the better apps out there, and the company did everything necessary to address the small things, like firmware updates. The app is clean, responsive, and intuitive. Obviously, the app is dramatically different than the iPad team system, and while the roles and functions of an individual device are easier to develop than an enterprise option, I like the app better. Training on your own or one-on-one is far different than the madness of a busy high school environment. Sets and reps are recorded in an efficient manner, and everything flows nicely. I have seen the system firsthand over a long period, and when I got my own individual system, it was even better.

Using the system during training pleased me. I was able to just train without the odd feeling of trying to work with a system—the system worked for me. I have experienced every system available, and even systems that are not commercially available. The FLEX was a great solution and didn’t miss reps, add phantom reps, or produce errors. The exercises are more extensive than many of the products out there, and they included many of the movements I need for a bread-and-butter workout. Adding workouts and exercises, changing loads, and using the system for feedback are well-executed in design. I do recommend a flat screen and Apple TV to connect the iPhone app. The company is working on an Android version, which is scheduled for release in early 2020.

FLEX is not an enterprise product or a team training solution, so know that it’s part of the equation and not a replacement, says @spikesonly. Click To Tweet

If you are looking for a portable travel product or something light, this is a good accessory for your training or something that could take care of testing needs if stretched to the max. Personally, I see the device as something different rather than a less-expensive GymAware option, as it doesn’t have the full set of tools and features provided by that system. Again, it’s not an enterprise product or a team training solution, so know that it’s part of the equation and not a replacement.

Cloud Services, Online Software API Details, and Data Management

Nearly every coach will ask about the cost of the software subscription to get their team data. If you use FLEX for a home gym or for private training, what you see is what you get. For managing multiple individuals, not actually team or group training, you will need to pay for a connection fee to the GymAware Cloud system. This is a little under $30 a month, and you pay it annually in a single payment. It is important to know that this cost is for the devices to connect and is not a license per sensor.

If you have an AMS that connects to GymAware Cloud, you can see FLEX data from anywhere in the world in near real time. You will not see it rep by rep, but by the time the athlete is drinking their protein smoothie, you’ll be able to see all of the data from the session. What is most compelling is the future of GymAware and FLEX, and how they will coordinate and navigate in the strength and conditioning software space.

My prediction, which does not represent the company’s vision, is that we will see more convergence of the companies that provide software for coaches. It’s up to the market to decide the standard of workflow for designing workouts, administering the training, and analyzing the data. The more the coach has to do monkey work, the lower the satisfaction and adoption rates. 

Mixed Environments with Mixed Results

A few coaches have asked whether using different Kinetic Performance systems is acceptable, or whether it’s okay to have products from different companies. My answer is that it’s possible to use different systems, but you should realize the limitations of not having interchangeable data or using a different system that produces invalid data. When working with barbell tracking, precision, accuracy, reliability, and validity are all different. Unfortunately, measuring a barbell isn’t as easy as measuring athlete speed, and even sports timing is difficult sometimes.

The FLEX is a very creative and unique way to get inexpensive barbell tracking without using an IMU, says @spikesonly. Click To Tweet

If you do wish to buy a few FLEX systems for correspondence coaching with professional or elite athletes, you can do it with confidence knowing that the data is nearly identical to GymAware. If you wish to use FLEX in a group setting to try to save on costs for the team, remember that it’s not designed for group training or enterprise usage. I have no clue what the company plans to do down the road, but the FLEX is a very creative and unique way to get inexpensive barbell tracking without using an IMU. If you are in a great environment that is receptive to technology in the weight room, pick up a system, as it is worth the small investment.

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