Accommodating resistance machines
Of course, moving a barbell or a stack of weights might to accomplish the same thing, but there’s actually a whole lot more at play.Inertia, acceleration, and other factors (like friction from cams and pulleys) can cause the amount of force on the body to change at various points throughout the movement.The pushup is a classic example of a constant resistance body weight exercise, as the weight load is the same on both the lowering and rising phases.
Today, it is well documented in the literature that the size of skeletal muscle is affected by the amount of muscular activity performed.
For a barbell bench press, for example, if you push the weight fast for the first half of the move, the barbell will become lighter, perhaps even weightless, during the second half of the motion due to momentum.
By comparison, with pneumatic resistance, no matter how fast you move, the resistance stays the same.
James Perrine first introduced the concept of Isokinetic exercise to the physical therapy profession in the late 1960’s.
Traditional weight lifting exercises are performed at variable speeds at a fixed resistance or weight.