Thera-Band tubing with attached handles is endorsed by the American Physical Therapy Association and utilizes the recognized Thera-Band system of progression and familiar colors pioneered over 30 years ago. The system of progression provides for consistent increase in resistance level to offer a measurable means of tracking progress.Each natural rubber tube supplied in Yellow Red Green and Blue resistance levels is 48" long while those supplied in Black and Silver resistance levels are 50" long. Use of the Thera-Band system of bands and tubing assures consistent and familiar resistance levels and assurance of professional grade quality.