How now, Horatio, you tremble and look pale.
Is not this something more than fantasy?
What think you on ’t?
— Barnardo
On our recent visit to Houston, TX, I had the opportunity to play around with Tonal, advertised as “The Worlds Smartest Home Gym”. I utilized this machine during five of my workouts over a period of two weeks. Rather than write a comprehensive product review (there are many resources for that), I’d like to subjectively share the felt experience. If I were to summarize it in two words; strangely sexy.
In simple terms, Tonal is a wall mounted interactive screen with adjustable cable columns. The resistance offered from these two cable columns is where sexy steps on the stage. Broadly defined as digital weight, here is a description of the technology from their website, “Physically the electromagnetic resistance engine within Tonal is a combination of computer chips, coils that generate an electromagnetic field controlled by those chips, and magnets that allow you to fight that field as you pull on a cable. It operates on some of the same physical principles as a traditional motor but with a far more advanced approach.” No pins, no weight stacks, but delivers up to 200 pounds (more on this number in a moment) of resistance, naughty!
In a small study out of High Point University, funded by Tonal, those 200 pounds are the “hypothetical equivalent” to the feel of 260 pounds of free weight. Writing that last sentence triggered a pet peeve I’ve had with the weather since childhood. If the temperature outside is 0º but when factoring in the wind chill it “feels like” -15º, well then for Pete’s sake its -15º. All this is to say that I agree anecdotally the selected weight on Tonal feels heavier than the numbers suggest. Why? Tonal’s explanation is that because the weight is generated by an electromagnetic motor the opportunity for momentum is reduced and more force must be generated to keep the cable moving.
From the users standpoint, it feels like someone or something is pulling back on you, Dr. Strange, please enter stage right. Tonal has a built in AI, dun-dun-dunnn! Ok before we get to that I should unpack the “someone or something pulling back on you” because its true regardless of the AI features. Manual resistance is the closest thing I can compare it to, e.g., lateral raises; partner up with someone and have them sit or stand behind you, let your arms hang down the side body while they place their hands on your wrists, they should apply force as you move your arms away from the body and up, once at shoulder height resist their force as they push back down and in to the staring position. If the person you’ve partnered up with knows what they’re doing they will be able to modify the amount of force they’re applying based on your strength profile, i.e., where you’re stronger vs. where you’re not. This is a form of what is commonly described as variable resistance training. Labeled on Tonal as dynamic weight modes, here is a list and short description of these features which are the AI’s digital take on VRT:
- Spotter — reduces the weight so you can finish a rep/set.
- Burnout — gradually reduces the weight in a high-rep set/digital drop sets.
- Eccentric — increases resistance during the eccentric phase and decreases during the concentric.
- Chains (we’re getting kinky now) — increases resistance during the concentric phase and decreases during the eccentric.
- Whips — just kidding.
- Smart Flex — described as combining the best elements of Chains and Eccentric modes.
The two modes I used the most and applied concurrently were Spotter and Smart Flex. Spotter pretty much worked as advertised. Trunk rotation was the exercise where I found it to be the most helpful. If the isometric position was held when motion stopped from the onset of fatigue, the weight would reduce until the rep was completed. If I attempted additional reps, the original weight would be added back on and these steps then repeated. My one critique is that Spotter should kick in just a bit sooner.
Smart Flex is ambitiously claiming to deliver what many consider to be the Holy Grail of resistance training, the perfect rep. But first, I feel the call to thank the humans behind the AI for naming it Smart Flex and not something like Samantha or Ava. Ok, what is the perfect rep? During any exercise there will be points of the range where you’re stronger and points where you’re not. This is due in part to mechanical advantage or disadvantage but will also change throughout a set as fatigue and other variables become a factor. I already used the term strength profile to describe this process during the lateral raise example above. But that only explains the bodies side of it. Resistance is relational and requires an external application of force. The perfect rep consists of an exercise where the external application of force matches our internal abilities to produce force throughout the entire range of motion, perfectly.
Susie Reiner, a science writer at Tonal, declares that Smart Flex “senses” these changes and scales appropriately, “when lifting a weight up in a biceps curl, the movement is easiest at the beginning, gets harder as you get closer to 90 degrees, and then gets easier again as you go past 90 degrees. Think about how you may sometimes get stuck in the middle through the center of the biceps curl. This is due to a longer moment arm (the weight is farther away in space from the body) at 90 degrees and requires more force from the muscle to overcome that disadvantage. On free weights, you can’t ditch weight to help you push through a rough patch and then dial it up on the parts of your lift where you’re feeling strong. But Smart Flex increases the weight at the beginning and end and lightens it in the center so you can challenge the weaker parts of the movement so you can easily progress to a heavier weight.” To put it politely, I’m calling bullshit.
A moment arm is a vital tool for determining how much influence a force has on motion around an axis. It is defined as the shortest distance from the line of force to that axis, which will always be perpendicular.
Imagine the arrow pointing down is the effect of gravity while holding a 10 pound dumbbell. The red line is the moment arm representing the influence that dumbbell has on motion around the elbow. Those 10 pounds will not represent 10 pounds of resistance until the force angle is at 90º which coincides with maximum moment arm length (center image). Once the dumbbell moves away from 90º, in either direction, its influence on rotation will decrease.
However, the bodies intelligence must be taken into account. In this image the arrow pointing up represents the attachment of the biceps muscle on the forearm. The red line connecting that arrow to the elbow is the moment arm of effort. Notice that it also reaches maximum length at 90º. So throughout this exercise, the bodies mechanical advantage is increasing and decreasing in concert with that of the dumbbells.
Add in what is understood about muscular length-tension relationships. In general, muscular tension is greatest when muscles are at an intermediate length, that is neither too short nor too long. Then Smart Flex, at least based on the statement above, has inverted the bodies strength profile by increasing weight at the beginning, reducing in the center, and increasing again at the end.
It would be superfluous to dive deeper into the realm of moment arms since I don’t actually believe this is something Smart Flex is able to determine, yet. Take the included deadlifting video as an example. Tonal boasts about leveraging multiple sensors to provide its unique technology called “Form Feedback”. But in order to determine moment arm lengths while I’m deadlifting would require at least one of these sensors be placed on the side of my body. Perhaps side sensors can be included in future iterations?
Tonal also tracks cable length data 60 times a second and I believe this to be the true hub of its “intelligence”. Essentially it’s making predictions, primarily based on the speed and distance traveled of the cable. Both Smart Flex and Spotter were activated during the above deadlift. You can see Smart Flex kick in on the second rep (Spotter didn’t factor into the set), oscillating between 175 pounds on the ascending concentric phase and 200 pounds on the descending eccentric phase. Since both the cable and I are clearly moving faster during the eccentric phase, the AI is predicting this to be where I am the strongest. As it is well acknowledged that eccentric muscular contractions are stronger and require less energy than concentric or isometric contractions (although the exact reasons why remains a partial mystery), this is a safe prediction to make. But this seems to have more accurately fit the description of an alternate mode, was Eccentric filling in at work for Smart Flex that day?
To give Tonal its due credit, I think they’ve created an extraordinary product with vast potential that’s just barely been tapped into. My experience deadlifting was better than anything I could have ever imagined possible with cables. Particularly mind-blowing were the qualities of reduced inertial effects caused by decreasing the resistance at strategic points in the range. Is this an intended outcome or just a happy accident? I believe an honest promotion of your product to date would be “The Worlds Best Cable Workout”. That being said, I find it rather amusing that all the funding, research, and innovation simply cannot eclipse a rack, a barbell, and some plates.
On one hand, I view Tonal as a unique and yes, strangely sexy, resistance training modality that I wish to become highly accessible. Sadly though, it seems destined to be relegated to high end hotels and home gyms. But then I read words like this by Reiner on Tonal’s blog, “Your movement is detected every second the cable is engaged on Tonal, so it can intelligently sense when Spotter mode needs to kick in. The same can’t be said of human spotters. It only takes one distraction for a spotter to look away, which can increase your risk of failure and injury.” So on the other hand, you silly distracted humans, I view Tonal as an unmalicious step in the direction of a technocratic transhuman agenda.
Thus, while you and your friends can be fun for the occasional rendezvous Tonal, I choose the iron over the electromagnetic, cold plunge over cryotherapy, traditional sauna over infrared, pranayama over hyperbaric chambers, silent darkness over meditation apps, intuitive awareness over wearable’s, and the Shakespeare’s over the Chat GPT’s.