The handheld Dynamax Core Trainer is designed to offer an upper-body and core workout with just 5 minutes of use per day, the company says. The Dynamax uses variable resistance to offer lighter or heavier workouts. After pulling the start-up cord, the DynaMax Core Trainer produces up to 200 pounds of resistance and flashes LED lights. The device is compact and portable and weights only 3.5 pounds. Available at www.dynaflexpro.com.