Wondercise adds arm and leg sensors to better track your exercise formBefore Apple Fitness+ debuted late last year, Wondercise was one of the many companies offering on-demand fitness classes you could take at home. The company's edge, though, is its Live Motion Matching system that uses wearables like the Apple Watch and Garmin devices to track your form while you're working out. The new straps are add-ons that can be used with either the company's own fitness band or third-party wearables that connect to the service, including the Apple Watch.