There is more to progressive resistance exercises than meets the eye. In fact, there is a language specific to resistance training. For example, resistance training exercises can be classified as isometric, isotonic, and isokinetic. The first part of each word, iso, means "the same." If we figure out what the last part of each word means, we’ll figure out what resistance training is all about.
Let’s start with isometric. Metric means "distance," so isometric exercises are same-distance exercises. More specifically, isometric exercises are exercises where the muscle remains the same length. Holding a push-up position is a good example of an isometric exercise. Another good example of an isometric exercise is a tug-of-war when the rope is not being moved by either team.
How about isotonic? Tonic means "tension," so isotonic exercises are same-tension exercises. That is, isotonic exercises require you move the same weight through a range of motion. A biceps curl is an example of an isotonic exercise. When you perform a biceps curl with a 10-pound (4.5 kg) weight, your muscles shorten and lengthen to move the weight up and down, but you’re always moving the same 10-pound weight.
Finally, let’s decode the word isokinetic. Kinetic means "movement," so isokinetic exercises are same-movement exercises. In other words, isokinetic exercises are exercises in which the speed of the movement remains constant no matter how much force you apply. Isokinetic exercises can be done only with specialized machines that are often used for rehabilitation from injury.
