It is the contraction where there is a great tension at the muscle level, but the insertion points do not vary, ie, the muscle is neither shortened nor lengthened, there is no movement.
Isotonic contraction, are divided into:
- Concentric contraction: It is also called positive contraction, there is muscle tension and shortening, is when muscle strength is greater than external force. The insertion points in the muscle are approaching.
- Eccentric contraction: Also called negative contraction, there is tension in the muscle and elongation. When the muscular force is less than the external force, the insertion points move away or separate. Like when we lower the dumbbell down doing biceps.
* Muscle fibers vary in all muscles, each one is composed of them, can be of fast or slow contraction, also called white fibers or red fibers. Some have a higher proportion and some have a lower proportion. It is said that the postural muscles have more slow fibers, when we train with weights and make explosive movements we use more fast fibers.
No person is the same as another, so it is important to know the difference between muscle composition in women and men. The predominant type of muscle fibers in people can determine their abilities; For example, if you wonder why there are people who perform better at short distances running or marathon runners who have to run for a long time and have greater resistance, it is because their muscles are composed mainly of some of the muscle fibers; The one who runs fast and does sprints has more fast fibers and the running marathon has slower fibers.
As the name implies, slow-twitch fibers contract more slowly and can be used for longer periods of time, athletes who run long distances need more fibers of slow contraction, they rely more on oxygen to obtain energy source.
Rapid contraction fibers provide strength and speed, but also fatigue faster, need fast and intense energy impulses and therefore require more rapid muscle fibers, they rely on ATP and glycogen as energy source, as the ATP is exhausted fast And lactic acid is a bioproduct of the use of glycogen, fast-twitch fibers can only be used for short periods of time.