Go Fit Ultimate Power Tube With Instruction / Core Performance DVD. The new Power Tubes are an ideal workout tool that can be used for both strength training and rehabilitation. The Ultimate Power Tubes include a training DVD with professional instruction from Mark Verstegen, a worldwide trainer of pro athletes and creator of the Core Performance® System. Join Mark, as he empowers you with his scientifically-proven exercises, to increase your balance, strength, and functionality, helping you feel better, have more energy and reduce pain for an active lifestyle.Go Fit strives for maximum performance and innovation in every product. Resistance tubes are not all created equal. GoFit Power Tubes are designed with a unique, reinforcing “Inner Cord” coil within the premium-grade tubing.