What Is Muscle And How Does It Work? A Quick Overview on Muscle Structure & Function that Every Lifter Should Know

Muscle Types

Skeletal muscle, getting its name by being attached to bones, is striated, which means that its made up of parallel fibers which look like bands. It is also called voluntary muscle because it only contracts based on the signals it receives from the central nervous system, and can be consciously made to contract or relax. These are the muscles that are responsible for creating voluntary movement that allows us to interact with the environment.

Smooth and Cardiac muscles have different functions and properties from that of skeletal muscle and are usually involuntary, not requiring nervous control. Blood flow regulation, movement of food through the digestive tract and contracting the heart are some of the main functions of smooth and cardiac muscles.

Kinetic Chain

Muscles cannot function without receiving orders from the nervous system, and they cannot produce movement without exerting force on the skeletal system(bones,tendons,ligaments). Together, the nervous, skeletal and muscular systems form the Kinetic Chain, the interconnected system that works in harmony to produce force or motion.

What they Do?

Muscle is typically in one of two states, either relaxed or contracted. In a contracted state they shorten, and in a relaxed state they lengthen. There needs to be some type of action that causes them to lengthen(relax), otherwise they will remain in a contracted state and become problematic.

Basically, during a contraction, force is exerted along a line. Think of it as the opposite ends of the muscle moving towards its center.


Muscle is typically set up with origin and insertion points. The origin is the end of the muscle that is anchored, linked to a bone that remains in a fixed position and doesn't move. The insertion point is the opposite end that is connected to a bone whose position is free to move.

Muscle is made up of 2 types of tissue, connective tissue and contractile tissue. Connective tissue is made up of proteins that don't actively contract, but they can store and release energy by being stretched like a rubber band. The main jobs of connective tissue is to help transmit force and protect the muscle by forming a barrier and prevent ripping.

Connective Tissue

The 2 types of connective tissue that make up a muscle's structure are tendons and fascia. Tendons either connect muscle to bone or muscle to muscle and are pretty elastic, although they are relatively stiff as well. This combination of stiffness and elasiticity comes from the structural proteins that tendons are made up of, collagen and elastin.

Fascia is the connective tissue that wraps the muscle in several layers from shallow to deep. It starts by wrapping the entire muscle(epimysium), then wraps a group of fibers(perimysium) and finally wraps each individual muscle fiber as well(endomysium). Basically, muscle fibers exist hand and hand with the various layers of fascia, from top, middle to deep. The fascia tissue is more elastic than tendons due to having a higher percentage of elastin, the "stretchier" structural protein.

Muscle Fiber(Contractile Tissue)

A muscle fiber is a large, extremely thick tubular cell. Recall from above that each fiber is wrapped by fascia tissue. The fiber, as a unit, is what provides the contracting force you need to lift weights.

Each fiber(cell) is made up of many chains of myofibrils, a rod-like unit that is in turn made up of bundles of myofilaments. Think of the fiber as the large cell that contains many myofibrils, which contain really tiny proteins called myofilaments.

  • Support System

Inside of a muscle fiber(cell), there are various support systems such as the sarcoplasm, mitochondria, nuclei and ribosomes. Basically, the sarcoplasm and mitochondria are structures inside which energy is produced from glucose, oxygen and more. The sarcoplasm and mitochondria are essential for producing useable energy that fuels muscle contraction. The nuclei and ribosomes are the source of new proten molecules that are formed with increases in strength and aerobic/anaerobic work capacity.

  • Membrane System

In addition to the support system, a muscle fiber also contains a membrane system which serves as the place where foods & wastes enter and exit and as a medium for communication/coordination. This membrane system is made of up of the sarcolemma, the t-tubule system and the sarcoplasmic reticulum.

The sarcolemma is the membrane surrounding the cell, controlling the nutrients and wastes that enter or exit the fiber. Its also the medium where action potentials, which are nerve impulses, are conducted. The t-tubule system consists of tubes that pass from one end of the cell to the other, allowing for action potentials(nerve impulses) to enter. The sarcoplasmic reticulum is a network of flat membranes that surround the myofibrils(rods) and control the storing and pumping of calcium ions that are essential to contraction.

  • Contractile System

Now that we know about the support and membrane systems inside an individual muscle fiber, the only thing left to cover is the contractile system. Recall that myofilaments are the tiny proteins that make up myofibrils. The myofilaments are made up of thick(myosin), thin(actin) and elastic(titin) filaments, and its the interaction of the thick & thin filaments that causes a muscle to shorten(contract).

Myofilament bundles are arranged together in a repeating structure called sarcomeres, which is a complete, functional contractile unit. A single muscle fiber contains thousands of sarcomeres that go from the relaxed to contracted state, producing the magic of force that allows us to train in the weight room.


  • Skeletal muscle is striated(band like) and voluntary(can be controlled consciously)
  • Muscle functions by receiving orders from the nervous system and exerting force on the skeletal system(bones, ligaments, tendons)
  • Muscle is made up of connective tissue and contractile tissue. Connective tissue includes 1)tendons, which connect bone to muscle or muscle to muscle, and 2)fascia, which wraps the muscle in several layers.
  • The contractile tissue, also known as the muscle fiber(cell), is made up of a 1)support system, 2)membrane system and 3)contractile system.
  • The support system inside a fiber includes the 1)sarcoplasm and mitochondria, which help to create energy, and 2)nuclei and ribosomes, providing a source for creating new protein molecules.
  • The membrane system inside a fiber includes the 1)sarcolemma, the membrane surrounding the cell through which food & wastes enter and exit, the 2)t-tubule system, the tubes that run from one end of the cell to the other, and the 3)sarcoplasmic reticulum, the internal flat membranes that control the release of calcium during contraction.
  • The contractile system inside a fiber is made up of the tiny myofilaments that are arranged together in a repeating sequence called sarcomeres. A sarcomere is a group of repeating myofilaments and it is the functional unit that shortens to create a contraction.