The X develops muscle and strength throughout a full range of motion. Terminology-wise, isometric contraction refers to the person’s maximum effort against an immovable object while isotonic is the muscle contraction through the full range of motion.
Put to practice by the X, an exercise begins with a 10-second isometric contraction, thereby fatiguing the muscle, then the isotonic phase takes over by working’ the muscle through a range of some particular football-necessary motion, It may be a passing motion for the quarterbacks, forearm motion for the linemen or leg, knee or foot motion for all.
The amount of resistance or weight from the X is controlled by a little lever on the handle, it ranges from 0 to around 400 pounds.
And of course you can use it with the long line to get your horzizontal resistance as shown in the video. Get it here: X