8 p.m. The gym. I picked up a medicine ball, stepped onto a balance trainer and squatted down into the first of 10 reps, holding for 10 seconds at the bottom. I’ve been working on a Bosu every other day as part of my physical therapy to build strength around a torn posterior cruciate ligament in my left knee, and I have a hard time focusing on distributing my weight evenly, especially early in the morning or late at night. But this workout was slightly different. Instead of sweats I was wearing compression shorts lined with eight electromyograpy, or EMG, sensors; instead of a mirror, I was staring into an iPhone screen giving me real-time visual feedback on which muscles were firing and how hard they were working; and instead of my physical therapist, Dhananja Jayalath, a hardware engineer, was telling me to engage my hamstrings and stop favoring my left leg.

MORE WEARABLES: Tested: Misfit Shine | Introducing the iBuckle, A Really Sweet Belt | A Case for the Traditional Watch

Jayalath has no background in personal training. Furthermore, he wasn’t actually looking at my form: he was looking at data — data streaming from my shorts. Jayalath is the CEO and co-founder of Athos (prounounced ah-thos), a startup that’s just a few months away from bringing to market compression clothing capable of monitoring how hard your muscles are working — on top of heart rate, heart rate variability and breathing patterns. The project started when he and co-founder Chris Wiebe were still in college studying electrical engineering at the University of Waterloo.

“Chris and I got tired of spending time at the gym and not knowing if we were getting the most bang from the buck”, Jayalath said. “How can we optimize, get more out of the time and know if our form is correct?”

They wanted the insights of a personal trainer without having to shell out $60 per hour. After several years of work on a prototype, a round of funding from Social+Capital Partnership (and another very recently led by DCM), and after adding a handful of engineers, designers and a neuroscientist to their team, their solution is about to hit the market. The product Athos offers is a pair of shorts (shipping November 2014) and a shirt (thereafter) equipped with a total of 22 EMG (14 in the shirt, eight in the shorts) sensors, four heart rate sensors (two each) and two breathing sensors (just the shirt).

From the outside, the warp-knit garments look, feel and behave like other high-end compression apparel: they have flat seam construction, four-way stretch, moisture-wicking properties, UPF 50 treatment and they’re machine washable. The only noticeable difference is a small docking station on the outer thigh of the shorts and the upper arm of the shirt, where the “Core” clips in. The Core is the so-called “brain of the system”, a 2.5-inch-long, 20-gram, ellipse-shaped wireless device complete with the hardware and software to collect biosignals and send them via Bluetooth to your phone, where they’re crunched and presented visually.

Athos apparel has all the same core functionality of these other wearable biosensors in addition to its use of EMG — the collection and evaluation of electrical activity produced by the muscles — which is a very big difference indeed.

For those who follow wearable biosensors closely, wired apparel is new but not brand new. The adidas miCoach training shirt has a heart rate monitor sewn right into the chest, offering an alternative to a chest strap. Mimo makes a wearable baby monitor that keeps track of breathing, baby position and temperature. At this year’s U.S. Open, Ralph Lauren launched the Polo Tech shirt, which collects information through conductive thread sewn into the shirt. Polo’s shirt is made by a company called OMsignal, which is launching its own brand of apparel with conductive thread to collect biometric information about heart rate and breathing. Hexoskin does basically the same thing, plus it monitors sleeping. These are, in other words, apparel versions of wearables already on the market, like the Soleus Go or the Jawbone Up24.

Athos apparel has all the same core functionality of these other wearable biosensors in addition to its use of EMG — the collection and evaluation of electrical activity produced by the muscles — which is a very big difference indeed. When we move, the cells in our muscles give off an electrical signal. Collectively, the mass of cells in our muscles produce a signal that can be read by placing electrodes, like those inside the Athos shorts, on the skin near those muscles. If you know what to do with this data it can tell you all kinds of things about muscles, including how hard they’re working and exactly when they’re fatiguing.

It’s no wonder then that EMG has been studied for decades and used clinically for sports medicine and rehabilitation. The key for Athos was making it available to everyday athletes at a price that wasn’t institutional (the Core is $200 and each item of clothing costs $100). As I manned a stationary bike to test the app’s cardio mode, I wondered how Athos had cracked the nut of interpreting the data. From my experience with endurance sports, I understood that the way to quantify your effort was to either measure it in watts (like with a power meter) or measure your maximum output (like with VO2 max), which is a gruesome affair.

“There’s a scientific concept called MVC, or ‘maximum voluntary contraction’”, Jayalath said. “What we deal with is an algorithm that can figure out your maximum voluntary contraction without you having to exert against it — because that’s not safe to do at home.”

Triathletes will all buy it; many will destroy relationships by refusing to take it off.

Instead of having the contract your muscle with peak force, all the Core requires is that you calibrate it first by walking up a flight of stairs. How Athos uses that information to figure out your peak force is part of their secret sauce; Jayalath was unwilling to divulge details. But as I looked at the app, it appeared they’ve figured it out: in real time, the screen displayed which muscles were activating, with different gradations of color indicating effort and fatigue.

To quote a friend: “Why would I need that?” There are a lot of different answers to this question. While we can all agree that Athos is fundamentally very neat and cool, it will be interesting to see how it’s received. Early adopters in the tech community will like the slick app and immediate feedback on their plyometric lunges. Physical therapy patients will like to see if they’re favoring muscles and by how much. Triathletes will all buy it; many will destroy relationships by refusing to take it off. It’s very likely that the Athos technology will also turn up in the apparel of more mainstream sports brands, like OMsignal did in Polo Tech. Meanwhile, other competitors are emerging: Finland-based Myontec is taking preorders for EMG-equipped shorts that they too have been developing for several years. The implications of such capable apparel are far reaching (and well discussed elsewhere), but suffice it to say that we’re not headed for a sci-fi world in which data streams from our shirts, shorts, sports bras, baby onesies and underwear: it’s already here.