This week saw launch announcements for three activity trackers: Jawbone's UP, Fitbit One, and pre-orders for Misfit Wearables' Shine. But even the best tracking data doesn't always lead to the behavior change necessary for sustained weight loss. That's where Retrofit comes in.

Retrofit, a year-old start-up formerly known as Strong Suit Wellness, announced an $8 million round of funding this week. The startup combines health tracking technologies with personalized instruction from trainers to deliver a managed weight loss action plan. Over the course of 12 months, customers can pay $259 a month for a program that aims to help them lose 10 percent of their body weight or $349 a month to lose 15 percent. The monthly fees include a Withings wireless weight tracking scale, a Fitbit activity tracker and weekly Skype sessions with a dietician, a behavior coach, and an exercise physiologist. The coaches will use the tracking data to help them tailor the weight loss plan for that particular customer.

The funding leader for the $8 million round of series A financing was Draper Fisher Jurvetson, a venture capital firm with investments in a number of companies, including Epocrates. DFJ contributed $6 million to the round. Other new investors were Correlation Ventures and Hyde Park Angels, with existing contributors New World Ventures and I2A fund also chipping in. This raise brings Retrofit up to $10.7 million in total funding, which they'll use to continue to develop the service and for acquiring new customers. The company currently has 80 full time employees and claims that 90 percent of their users are losing weight.

Given the price tag, Retrofit is obviously a high-end weight loss solution, but the company does offer need-based scholarships on their site. Retrofit also announced the Retrofit My Company contest Tuesday. Applicants write a 500-word essay for a chance to win a year of free Retrofit service for up to 100 people at their company, a $300,000 value.