Muscle Movement & Contraction

Lesson Overview

In this lesson, we introduce the anatomy of muscle movement through muscle contraction.

Objective

Gain an understanding of how muscles move and learn the related terminology.

Description

Explain the purpose of muscle and how muscle movement happens. Define muscle contraction and explain how origin and insertion points relate to it. Name three types of muscle contraction and provide an example for each. Explain the agonist and antagonist muscle relationship and reciprocal inhibition, and how to use this knowledge in practice. Explain muscle cramping, why a muscle might cramp, and what might help.

The Function of Muscles

Muscles provide the force behind movement. Muscles are the only tissue in the body that have the ability to contract and therefore move other parts of the body.

Our focus here is on the way that muscles move bones. In addition, muscles are also responsible for:

  • Movement of blood and lymph
  • Expansion and contraction of the lungs
  • Movement of solids and fluids through the digestive tract

How Does Movement Happen?

  • Movement is produced by muscle fiber (bundles of specialized cells) changing shape (contracting or relaxing).
  • Muscle fibers contract in response to the Central Nervous System.
  • The force of the contraction is transmitted to the fascial elements surrounding the muscles and eventually on to the bones, moving the joint. (Ray Long)
  • See also Flexibility & Stretching.

Relationship of Muscles in Movement

Agonist / Antagonist Relationship

  • When one muscle contracts, another muscle stretches.
  • Flexing the elbow (to draw forearm up) contracts the bicep (called the prime mover or agonist) and stretches the tricep (called the antagonist).

Agonist / Prime Mover + Synergists

  • The agonist muscles are also called the prime movers.
  • These muscles provide the predominant contraction for the movement.
  • The provide the major force.
  • Synergist muscles contract along with the prime movers to help carry out the motion.

Antagonist

  • The antagonist performs motion in the opposite direction of the agonist muscles.
  • These muscles stretch passively.
  • They typically relax (but not always).

Another Function of Antagonist Muscle

The antagonist doesn’t always relax though; another function of antagonist muscles can be to slow down or stop a movement.  We would see this if the weight involved in the bicep curl was very heavy, when the weight was being lowered from the top position the antagonist tricep muscle would produce a sufficient amount of tension to help control the movement as the weight lowers. – PT Direct 

Examples

Following are examples of muscle pairs, some of which overlap because the list includes both general and specific relationships that may be useful to you.

  1. Biceps — Triceps
  2. Back — Chest
  3. Middle Trapezius — Serratus Anterior
  4. Trapezius & Rhomboids — Pectoralis Major
  5. Posterior Deltoid — Anterior Deltoid
  6. Abdominals — Lower Back
  7. Left External Obliques — Right External Obliques
  8. Rectus Abdominis — Erector Spinae
  9. Deltoid — Latissimus Dorsi
  10. Quadriceps — Hamstrings
  11. Gluteus Maximus — Iliopsoas
  12. Gluteus Medius — Adductors
  13. Shin — Calf
  14. Tibialis Anterior — Soleus & Gastrocnemius

See much more detail: Key Muscle Pairs in Movement – Agonist / Antagonist Relationship.

Stabilizer / Fixator

Three Things

To truly move a bone at its joint, three things must occur. A set (or two sets) of muscles must contract, another set must release, and a third set must stabilize. – Susi Hately Aldous

  • The stabilizer does not perform movement.
  • It fixes part of the body so that movement can occur.
  • It stabilizes the origin of the prime mover and the joint that the origin spans.
  • “The better the stabilizers are able to do their job, the more easily the movement will occur and the more fluid the pose.” (Susi Hately Aldous)

Reciprocal Inhibition

  • Reciprocal inhibition is an unconscious spinal reflex that causes the antagonist muscle to relax when the agonist muscle contracts.
  • We can consciously access this reflex to deepen stretches by first holding a mild stretch until the body has acclimated and then engaging the opposing muscle to go deeper. (Bandha Yoga)
  • See also: Active Stretching in Flexibility & Stretching.

It makes sense that there would be a corresponding physiological Yin/Yang to make biomechanical processes such as flexion and extension of the knee energy efficient, i.e., when the agonist muscle contracts, its antagonist relaxes. This process occurs unconsciously through a primitive spinal cord reflex arc that scientists call “reciprocal inhibition.” We can consciously access this reflex arc to deepen and improve our poses. –  Bandha Yoga 

Muscle Contraction: Origin & Insertion

  • Muscle contraction is the activation of tension in muscle fibers.
  • Some sources incorrectly define muscle contraction as the muscle shortening; in fact, the muscle may lengthen, shorten or stay the same.
  • Origin and insertion points are where muscles are attached to bones in relation to a movement at a joint.
  • As muscles contract, usually one end of the muscle remains fixed and the other end moves.
  • The attachment site that doesn’t move during contraction is known as the origin; the attachment site that moves is known as the insertion.
  • Different movements can cause a “functional reversal” of the origin and insertion points for a muscle.

Origin

  • Proximal (near) attachment of muscle to bone
  • On the bone that is relatively or usually stationary

Insertion

  • Distal (away) attachment of muscle to bone
  • On the bone that is most generally moved

Example: Flex Elbow

  • When looking to determine origin and insertion for biceps and triceps in flexing elbow, note that the arm is fixed, and the forearm moves
  • Origin: arm and shoulder
  • Insertion: forearm

Why Should We Care?

In Yogabody, Judith Lasater xplains that knowing where a muscle arises and ends will help with understanding of the action that a muscle can make and what might be going wrong if that muscle is not doing its job.

Origin & Insertion Points for Various Actions

Sources use different approaches in how they display muscle actions and their origin and insertion points, and to what level of anatomical detail they include.

Sometimes action is noted in terms of the appendage that is moved (e.g. flex forearm); more often, the action is described by the joint action (e.g. flex elbow).

Here are some sources for lists of origin and insertion points:

Types of Contraction

Isometric vs. Isotonic

If no movement takes place (the muscle doesn’t change length), it is called an isometric contraction. When there is movement, it is called an isotonic contraction.

Concentric Contraction

  • Causes movement against gravity
  • Muscle actively shortens
  • Example: raising weight during a bicep curl
  • Asana Example: Raising arms forward up—anterior deltoid and biceps contract concentrically

Eccentric Contraction

  • Slow down movement with gravity
  • Muscle actively lengthens
  • Example: walking (quad actively lengthening)
  • Asana Example: Controlled lowering of arms from overhead down to sides—biceps and anterior deltoid contract eccentrically

Isometric Contraction

  • “Static contraction”
  • Muscle activated but no change in length
  • Bones do not move
  • Example: Carrying an object in front of you; or muscle attempts to push or pull something immovable
  • Asana Example: Tadasana (Mountain Pose) or holding another pose for some time without changing body position

More Examples

Susi Hately Aldous gives this clear example, focusing on the quadriceps muscles:

Move from Tadasana (Mountain Pose) to Utkatasana (Chair / Fierce Pose):

  • Tadasana — Isometric contraction of quads
  • Into Utkatasana — Eccentric contraction of quads
  • Stay in Utkatasana — Isometric contraction of quads
  • Back to Tadasana — Concentric contraction of quads

Describing Phase of a Movement

Concentric and eccentric are also terms used to describe the phase of a movement.  The concentric phase is the phase of the movement that is overcoming gravity or load, while the eccentric phase is the phase resisting gravity or load.  So for push-ups the concentric phase is the up phase where gravity is overcome, and the eccentric phase is the downward phase where gravity is resisted. – PT Direct 

Why Do Muscles Cramp?

  • Muscle cramping is sudden, involuntary muscle contraction which causes pain.
  • Causes can include pregnancy, medications, liver disease and exercise.
  • In the case of exercise or movement, the ultimate cause of the cramp may be oxygen deprivation.
  • Deep breathing and bringing circulation to the area may help to prevent or resolve cramping.

Increasing Oxygen & Circulation to Tissues

Muscle cramping can be related to pregnancy, medications or liver disease. In many instances, it may be the result of exercise or movement and in these cases, the cause may be as Leslie Kaminoff explains in this 1-minute video. He explains that the sensation of a muscle cramping is a result of oxygen deprivation—which is associated with muscles that are weak. He explains that breathing delivers oxygen to the tissues and suggests that if there is cramping, to first “wake up” the muscles and bring more circulation to them.

Muscles Contract, Causing Pain

During a cramp, your muscles suddenly contract (shorten), causing pain in your leg. This is known as a spasm, and you cannot control the affected muscle. The cramp can last from a few seconds to 10 minutes. When the spasm passes, you will be able to control the affected muscle again. – NHS 

Cramping Can Affect Any Skeletal Muscle

A cramp is an involuntary and forcibly contracted muscle that does not relax. Cramps can affect any muscle under your voluntary control (skeletal muscle). Muscles that span two joints are most prone to cramping. Cramps can involve part or all of a muscle, or several muscles in a group…. Some researchers believe inadequate stretching and muscle fatigue leads to abnormalities in mechanisms that control muscle contraction. Other factors may also be involved, including poor conditioning, exercising or working in intense heat, dehydration and depletion of salt and minerals (electrolytes). – Ortho Info