Accommodating resistance devices
For example the drive phase (foot in contact with ground) of sprinting typically occurs with knee flexion of about 135degrees or greater and the same can hold true (not always, though) for some of your best performers in the vertical jump test. An athlete may max out at 315 in the parallel squat, but may max out at 375 in the quarter squat.
The limiting range of motion of the parallel squat is parallel (bottom position with joint angle of roughly 90 degrees), and for the quarter squat it may be 130 degrees.
The major hip extensors are the gluteus maximus, adductor magnus, and hamstring musculature (biceps femoris, semimemranosis, semitendinosis).
In 2002 Caterisano et al conducted a study on thigh muscle contribution during the partial, parallel, and full squat.
Typically force is generated in only one plane of motion, with minimal recruitment in other planes.
Band resistance lies on the opposite end of the spectrum as free weight training.
At the beginning range of motion, the band will have minimal if any resistance.
As the athlete progresses through the range of motion, the resistance increases, with the greatest resistance being at the end range of motion, where most sporting movements occur.
Taking into account joint angles and accommodation of these angles for transfer of training, this method of training makes sense.