Thera-Band 50-Yard Exercise Band by Power Systems. Thera-Band exercise bands are low-cost, portable, and versatile resistance products. Endorsed by the American Physical Therapy Association (APTA), recognized worldwide as the original System of Progressive Resistance. Can be used while traveling, sitting at home, or even in the office. 8 color-coded resistance levels determined by thickness. Available in 6 and 50-yard dispenser boxes.