What Is Muscle Fiber Contraction?

Exercise is all about these three types of muscle fiber contraction

Arm Muscle, Drawing. Credit: BSIP / Contributor / Getty Images

Muscle contractions (also known as muscle fiber activations) occur when a muscle fiber or group of fibers is signaled by the brain via nerves to activate and increase the tension within the muscle. 

Our muscles are made of bundles of muscle fibers that contain thousands of smaller structures called myofibrils, where the actual contraction occurs. There are two types of protein filaments within myofibrils called actin and myosin.

Myosin is a "molecular motor" that converts chemical energy into mechanical energy, which creates force and drives motion.

These two proteins, myosin and actin, interact with one another by sliding past each other, creating tension during muscle contraction. These molecular mechanisms are not fully understood. This theory is referred to as the "sliding filament model," and is used as the basis for understanding muscle contraction by biologists. 

The sliding filament theory explains that when a muscle is activated and movement occurs, these two interlocking filaments can grab onto each other and pull, which causes the myofibril to shorten. This shortening is called a muscle contraction.

There are three types of muscle cells in the human body:

  • Skeletal muscle: Drives voluntary movement.
  • Cardiac muscle: Cells of the heart that pump blood.
  • Smooth muscle: Cells responsible for involuntary movements of the body, such as the stomach and intestines.

    Three Types of Muscle Contraction

    There are three ways a muscle fiber can be activated. Two allow for movement in the muscle and one simply creates tension, without joint movement. The three contraction types include:

    • Eccentric Muscle Contraction (lengthening) - In weight training, this is the phase in which the muscle returns to the starting position of the exercise.
    • Isometric Muscle Contraction (static) - Isometric exercises are those that do not cause joint movement. An example is pushing against a wall.

    Learn More About Muscle Physiology

    Continue reading about how the muscles work, and then how this knowledge can be applied to benefit your fitness and training.

    Continue Reading