If your goal is to build upper body strength and increase shoulder flexibility, look no further than the RopeFit Heavy Jump Rope ($40). This 1.5-inch thick rope weighs about five pounds and comes in two lengths: nine feet (recommended for people under 5'10"), and 10 feet (for those who are taller). Because it's hefty, this rope is meant as a plyometric supplement to be used for short intervals. While advanced athletes may find this equipment a welcome addition to their HIIT workouts, the major downside is that the rope does not have detachable handles and is not adjustable.