A Detailed Comparison Between Flexion and Extension

Comparison Between Flexion and Extension
Flexion and extension are the movements of muscles that occur in the sagittal plane. Flexion causes bending while extension causes straightening. Here's a comparison between the two.
Bodytomy Staff
Last Updated: Mar 5, 2018
Most exercises are known to use both flexion and extension. Squats is a well-known exercise in which both hips move from extension into flexion, and then back into extension. Here the hips and knees spend more time in flexion.
Flexion and extension refer to movements of muscles about the joints. Whether a movement at the joint qualifies as flexion or extension depends on the direction in which it takes place and on whether it increases or decreases the angles between the body parts involved. Both these movements occur in the sagittal plane, which is a vertical plane dividing the body into left and right.
What is Flexion?
Flexion refers to the bending motion of joints wherein there is a decrease in the angle between the adjoining bones. Downward flexing of the foot or toes is referred to as plantar flexion. Turning the foot or toe upward is known as dorsiflexion.
What is Extension?
Extension is the exact reverse of flexion. It refers to the unbending motion of a flexed joint wherein there is an increase in the angle between the adjoining bones.
Both flexion and extension can be carried out in the thumb, wrist, arm, knee, shoulder, hip, and spine. These movements are possible with the synovial joints in the body.

Neck: When you move your chin towards your chest, your neck is flexed. When you extend your neck behind as if you were looking at the ceiling, it is extension.

Shoulder: When you raise your arm above your head, your shoulder is flexed. When you lower your arm and take it behind you, it is extended.

Knee: When you move your lower leg towards the back of your thigh, your knee is flexed. When you move your lower leg away from the back of your thigh, or in short, straighten it, it is knee extension.

Wrist and Thumb: When the palm bends towards the arm, it is wrist flexion, while extension is when it bends away from the arm. Moving the bone below the thumb towards the hand is thumb flexion. Moving it away from the hand in extension. The extensions and flexions of the thumb and wrist, considered as range-of-motion exercises, are believed to be among the commonly recommended exercises for hand and wrist problems.

The image below depicts the flexion and extension movements of different parts of the body. This illustration should help you understand the movements better.
Neck shoulder and knee flexion
Neck Shoulder and Knee Flexion
Neck shoulder and knee extension
Neck Shoulder and Knee Extension
Flexion Vs. Extension
◼ It is a bending movement of certain joints that causes a decrease in angle between the adjoining bones.

◼ It is a movement that is reverse of flexion, causing an increase in the angle between the adjoining bones.
Instigated by
◼ Muscle contraction

◼ Muscle expansion
Muscles involved
◼ Here it is said to be initiated by the agonist and opposed by the antagonist.
  • That is, in a flexed elbow the biceps are agonist and the triceps are the antagonist.
◼ Here, the roles are reversed, and it is initiated by the antagonist and opposed by the agonist.
  • That is, in an extended elbow the triceps are the agonist and the biceps are the antagonists.
The aforementioned comparison should prove beneficial in understanding the two terms in a better way.
Woman hands