Skeletal muscles connect bone to bone with tendonous attachments. When they contract, the bones generally pull closer together or flex which creates movement such as pedaling in cyclists.
Skeletal muscles are activated through electrical impulses from motor nerves. This activation triggers a chemical reaction causing muscle fibers to contract. The more muscle fibers that contract, the more powerful the muscle contraction.
Since muscles can only provide movement through contraction, they generally operate in pairs. One muscle acts in opposition to the another muscle. When one muscle contracts, the opposing muscle must relax
Skeletal muscle is controlled by the somatic nervous system (SNS). It is considered voluntary muscle since it is under our conscious control, especially when first learning specific tasks such as riding a bicycle.
Normally the muscles act together in a coordinated manner, producing smooth, efficient movements.
There are two basic categories of skeletal muscle – fast twitch (also referred to as fast glycolic or Type IIB) and slow twitch (slow oxidative or Type I). Within the fast twitch there is a second category sometimes referred to as intermediate, Type IIA, or fast oxidative fibers. Each has their own set of characteristics and purpose.
The percentage of fast, slow and intermediate twitch muscle fibers varies from person to person. The proportion is determined by genetics but can change with physical conditioning. Certain hormones, such as human growth hormone (HGH), testosterone and thyroid hormones can also stimulate the metabolism and size of muscle fibers.