Types of movements in the human body

Knee

Flexion and extension of the knee consist of the following:

• Anatomical structures: The tibia of the leg moves relative to the femur of the thigh.
• Reference axes: The movement is in the sagittal plane. The fulcrum is provided by the knee joint, through which the frontal/coronal axis passes.
• Direction: During flexion, the leg moves backwards (posteriorly). During extension, it moves forwards (anteriorly).

Elbow

Flexion and extension of the elbow joint can be described as follows:

• Anatomical structures: The forearm moves relative to the arm. More precisely, the ulna (one of the two forearm bones) moves relative to the humerus (bone of the arm).
• Reference axes: The movement is in the sagittal plane. The fulcrum is provided by the elbow joint, around a frontal/coronal axis .
• Direction: During flexion, the forearm moves upwards and ‘closer’ to the arm, resulting in a decreased angle between them. During extension it straightens, increasing the angle relative to the arm.

Shoulder

Flexion and extension of the shoulder occur like this:

• Anatomical structures: The humerus of the arm moves relative to the scapula of the shoulder blade.
• Reference axes: The movement is in the sagittal plane. The fulcrum is provided by the shoulder, or glenohumeral joint, around a frontal axis.
• Direction: During flexion, the arm moves anteriorly and upwards (in full flexion). During extension of the arm/shoulder joint (from a flexed position), the arm moves posteriorly and downwards, back to the anatomical position. If a full range of motion is performed, it can continue posteriorly, creating an imaginary arc or semicircle.

Neck

Flexion and extension of the neck follow the format below:

• Anatomical structures: The skull and cervical vertebrae of the neck move relative to the thoracic vertebrae and upper back.
• Reference axes: The movement is in the sagittal plane. The ‘fulcrum’ is not fixed due to the anatomy and movement of the cervical vertebrae, but it can loosely be positioned through the upper thoracic vertebrae. Movement occurs around a frontal/coronal axis.
• Direction: During flexion, the head and neck move anteriorly and downwards (in full flexion). Essentially, you are looking down. During extension, it moves posteriorly and slightly downwards.

Vertebral column

Flexion and extension of the vertebral column follow the following movement template:

• Anatomical structures: The vertebral column moves relative to the sacrum and hip bone.
• Reference axes: The movement is in the sagittal plane. You can imagine the ‘fulcrum’ as being loosely through the two hip bones and sacrum. Movement occurs around a frontal/coronal axis.
• Direction: During flexion, when you are bending forward, the vertebral column moves anteriorly and downwards (in full flexion). During extension, it moves backwards and slightly downwards.

Foot

In the world of anatomy, flexion of the foot is referred to as dorsiflexion and plantarflexion. Both movements happen at the ankle joint. Dorsiflexion means flexion of the dorsum (top) part of the foot by reducing the angle between it and the anterior surface of the leg. It happens when you lift the front part of your foot while keeping your heel on the ground.

Plantarflexion is flexion of the plantar (underside) part of the foot by moving it down. This movement happens when you are standing on your toes or pointing them.

Arms & Legs

The easiest examples for understanding abduction and adduction are the legs and arms, which are very similar:

• Anatomical structures: The arm moves relative to the trunk and the shoulder. The leg moves relative to the hip.
• Reference axes: The movement is in the frontal plane. You can imagine the ‘fulcrum’ as axes that pierce the shoulder and the hip respectively, each one following in a forward-backward trajectory.
• Direction: During abduction, you are moving your arm/leg away from the median plane. During adduction, you are moving them towards the median plane. To picture these movements, imagine a child jumping and flailing his/her arms very excitedly in order to grab your attention.

Digits

The digits of the hands and feet are also capable of abduction and adduction, but in a slightly specific way. The movements are also related to the medial plane, but this time to the medial plane of the palm or foot, not the body itself.

• Anatomical structures: The digits move relative to the third finger of the hand or the second toe of the foot. These two entities represent the medial planes.
• Reference axes: The movement can be in multiple planes, depending on the orientation of the hand or foot.
• Direction: During abduction, you are moving the digits away from the third finger or second toe, hence spreading them apart from the medial plane. Adduction is the opposite - the digits are brought closer.

Mandible

Protrusion and retrusion of the mandible occur as follows:

• Anatomical structures: The mandible moves relative to the viscerocranium (fused bones of the skull forming the face)
• Reference axes: The movement is primarily of a 'sliding/gliding' nature, and occurs in the sagittal plane. A very slight degree of rotation will also occur around a frontal/coronal axis.
• Direction: During protrusion, the mandible moves directly anteriorly (think underbite). During retrusion, it moves directly posteriorly (think overbite).

These movements are sometimes interchanged with protraction and retraction. However, the latter pair have an additional movement added to them. Protraction is not only an anterior movement but an anterolateral one as well. This means that the structure moves forwards and laterally. Similarly, retraction also consists of an extra posteromedial movement. The scapulae are the standard example of bones that perform protraction and retraction.

Mandible

The template for the mandible is as follows:

• Anatomical structures: The mandible moves relative to the viscerocranium (fused bones of the skull forming the face)
• Reference axes: The movement is in the frontal plane. It has a ‘fulcrum’ due to the nature of the temporomandibular joint, which is the transverse plane passing through the two respective joints.
• Direction: During depression, the mandible moves directly downwards. During elevation, it moves directly upwards. You are performing these two movements when you open and close your mouth or during mastication.

Head

• Anatomical structures: The head turns relative to the trunk.
• Reference axes: The movement is in the transverse plane. The ‘fulcrum’ is the longitudinal/vertical axis passing up and down through the vertebral column and the crown of your head.
• Direction: These two movements happen by changing the position the nose is pointing to. Turning your head laterally corresponds to lateral rotation, while turning it back to look straight ahead corresponds to medial rotation.

Arm/leg

• Anatomical structures: The anterior surface of the arm/leg turns relative to the trunk.
• Reference axes: The movement is in the transverse plane. The ‘fulcrum’ is the longitudinal/vertical axis passing up and down through the arm/leg itself.
• Direction: These two movements happen by changing the position of their anterior surfaces. By bringing your biceps/vastus muscles towards the midline, you are rotating them medially. If you orientate them in the opposite direction, you are rotating them laterally. For instance, if you are holding a newborn baby, your arms are medially rotated.

Mnemonic

Pronation and supination are very similar and easily confused. Use the following mnemonic to never confuse pronation and supination ever again!

Supinate to the Sun and Pronate to the Plants

• Supinate: palm towards the Sun
• Pronate: palm towards the Plants
  

Mnemonic

In order to easily remember the muscles that produce inversion and eversion you can use the mnemonic called "Second letter rule":

Eversion muscles

• pEroneus longus
• pEroneus brevis
• pEroneus terius

Inversion muscles

• tIbialis anterior
• tIbialis posterior