Battle Ropes (30-foot, 1.5-inch diameter)

Battle ropes are the most unexpected entry on this list and the most common reaction from people who try them is that they did not realize how hard they would work in 60 seconds. A 2014 Journal of Strength and Conditioning Research study found 10 minutes of battle rope intervals produced cardiovascular and metabolic responses equivalent to high-intensity interval training on a stationary bike, with the added benefit of upper body muscular endurance development. The ropes require a wall anchor point (included) and approximately 20 square feet of floor space to swing them. At $80-120 for a 30-foot poly-dacron rope from Onnit or Battle Ropes USA, they are a complete conditioning tool for anyone whose primary cardio limitation is boredom with traditional methods. The practical constraint: outdoor or garage use is strongly preferred — indoor use hits walls and requires careful spatial planning.