LOS ANGELES, CA - JULY 14:  Actress Hilary Swank attends the 2015 Sports Humanitarian Of The Year Awards at The Conga Room at L.A. Live on July 14, 2015 in Los Angeles, California.  (Photo by Paul Archuleta/FilmMagic)

Paul Archuleta

The pro: Grant Roberts, L.A. trainer responsible for Swank’s Million Dollar Baby bod Our tester: Kim Peiffer, InStyle.com managing editor and unofficial fitness model of the office

InStyle Staff
Jan 06, 2016 @ 11:00 am

“Truth be told, I’m a total gym fanatic. But even though I spend a few evenings a week—and consequently a good portion of my paycheck—sweating regularly, I’m pretty unaware of how hard I’m really working my muscles. I showed up at Roberts’s L.A. studio sporting a fresh pair of Athos’s connected capris [$149; liveathos.com]. They’re basic black but feel a bit bulkier than my usual Lululemons, thanks to 12 built-in biosensors that monitor your heart rate and muscle movements.

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"The concept is simple yet incredibly advanced: Charge the discreet Core sensor, and pop it into the slot on the pant leg so the bottoms are connected to your smartphone via bluetooth. Then fire up the corresponding app [Athos, free; available on iTunes] to get a real-time map of your body’s movements.

#FitnessFriday! #SledPushes #LetsDoThis #NoExcuses @grantrobertsfit #NoFilter

A video posted by Hilary Swank (@hilaryswank) on

"After Roberts and I discussed my fitness goals—bursting through plateaus, toning those leg muscles, and eliminating lower-back pain—we hit the gym floor. The pants are compatible with any type of exercise, but we began with a series of simple moves, like biceps curls, crunches, and shoulder presses. As I performed each one, Roberts followed along on the app to show me exactly what muscles I was using and underusing.

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"It turned out I was working my left side more than my right, meaning my left muscles risked overdevelopment. Another realization? I thought I was pushing myself as hard as possible, but according to the app, I was exerting only between 60 and 80 percent of my energy.”

The results: “My savvy coach noted that this imbalance contributed to my ongoing back issues, so being conscious of shifting my weight during workouts has helped ease those pains. In the weeks that followed, I’ve had the app running during every workout. Because it helped me put in extra effort, I’ve dropped 2 percent body fat and 5 pounds in four weeks. Plateaus, no more.”

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