Whoop CEO Will Ahmed

Boston-based startup Whoop raised $6 million to build out its continuous heartrate-sensing wristworn activity tracker, according to an SEC filing. This brings the company's total announced funding to $9.6 million to date.

In the most recent filing, Atlas Venture Partner Jeff Fagnan was listed as an investor, he's also an investor in Streetwise Media, which first broke the news on the funding round in its publication Bostinno.

Whoop plans to create a device that continuously monitors the wearer's heart rate, quantifies the intensity of their workouts, and monitors how much recovery time the user needs. The device is not designed for casual users but rather for athletes.

Founder and CEO Will Ahmed  explained on the company's employee page that he founded the company as a senior at Harvard as a collegiate athlete "looking for real quantifiable feedback". Ahmed's "extensive physiology research is the backbone for [the company's] data analytics platform". 

Whoop spun out of Harvard's Innovation Lab, which likely helped it land some big name advisors, including MIT Media Lab Founder Nicholas Negroponte, former Puma Chief Marketing Officer Antonio Bertone, and UCSF Chief of Cardiology Dr. Jeffrey Olgin.

In a December 2012 interview with the Boston Globe, Ahmed explained that when the company is ready to launch the device, it will market the wearable through coaches and trainers. The article also explains that Ahmed hopes his product will be a replacement for the common form factor for athletic heart rate sensors: the chest strap.

While there are not as many activity trackers on the market that track heart rate continuously, one that does is Basis, which was recently acquired by Intel. On Basis’s website, however, the company explains that its device cannot measure measure heart rate while the user is moving. As a result, Basis adds, their device can't replace a chest strap that monitors heart rate during workouts. (Correction: An earlier version of this article inaccurately stated that BodyMedia's FIT has continuous heart rate monitoring built-in. While the Core 2 does work with a third party chest strap, the device itself does not include this feature. The company told MobiHealthNews it would at some point, but has not yet delivered on it.)