AquaCross™ system enhances a variety of fitness and swim routines to increase muscle and burn more calories. This easy to use resistance tether provides counter resistance and stability to boost your training effectiveness and improve swim technique. Use the AquaCross™ system to master each stroke or kick your low-impact workout up a notch to intensify the total body effects of aquatic exercise (Standard on Synergy™ Series and Summit™ Series, optional on Vitality™ Series)