Reading Notes: What happens when you stretch?

1. "When a muscle is stretched, some of its fibers lengthen, but other fibers may remain at rest. The current length of the entire muscle depends upon the number of stretched fibers." When a muscle is stretched, the fibers of the sarcomeres lengthen. The length of a muscle when it's stretched depends on how many of the fibers in the sarcomeres are stretched and how many remain at rest. The more a muscle is stretched, the more fibers are stretched, and so the longer it will be.

2. "There are two kinds of muscle fibers: intrafusal muscle fibers and extrafusal muscle fibers." Extrafusal fibers are made up of myofibrils and have intrafusal fibers (a.k.a muscle spindles) that lie parallel to them. Both of these fibers work and move together when muscles stretch. Thus, when a muscle lengthens, they lengthen together and when muscles contract, these fibers contract together.

3. "With extensive training, the stretch reflex of certain muscles can be controlled so that there is little or no reflex contraction in response to a sudden stretch. While this type of control provides the opportunity for the greatest gains in flexibility, it also provides the greatest risk of injury if used improperly." When a muscle is suddenly stretched, the result is generally a reflex contraction. This is why we generally hold stretches for a couple minutes and must ease into and ease out of them: to avoid the reflex contraction, as it can make muscles much more prone to injury.

Relate and Review:

In this article, I learned that there are many ways by which muscles work together and stretch. When a muscle stretches, the sarcomeres (bundles of muscle fibers) spread out and elongate. Because the connective tissue simultaneously stretches with the sarcomeres, the muscle fibers lengthen. One of the main sources of body perception are sensory receptors in the muscles known as proprioceptors. The two main kinds of muscle fibers are extrafusal fibers and intrafusal fibers, which run parallel to the extrafusal fibers. These two fibers work together to enable stretching of the muscles. There are also two types of muscle fibers: nuclear chain fibers and nuclear bag fibers. Nuclear chain fibers are generally used in static stretching, which nuclear bag fibers are used in dynamic stretching. This relates to the Wellness Project that I did last semester about static and dynamic stretching and furthered my understanding of how muscles work differently depending on what kind of stretch is being done.