Forces in Rehabilitation

Original Editor - Alicia Fernandes Top Contributors - Alicia Fernandes, Vidya Acharya, Olajumoke Ogunleye, Kim Jackson and Carina Therese Magtibay

Introduction

A force is a push or pull acting upon an object as a result of its interaction with another object.

Types of Force

1. Internal Force: This type of force originates from actions occurring within the object itself. Examples include the contraction and relaxation of muscles, such as those involved in walking, and the pulling of muscles at their attachments to the human body.
2. External Force:External force is exerted on an object by an external agent. Examples include kicking a football, throwing a javelin, or pushing a rug. External force can be further classified into two categories:

• Contact Forces: These forces involve direct contact with the object and are required to change its position. Examples include pushing, pulling, tension, compression, hitting a tennis ball, or trapping a soccer ball.
• Non-contact Forces: Non-contact forces do not require physical contact with the object. Examples include magnetic forces, which attract metallic materials to a magnet, and gravitational forces, which attract objects to the Earth's surface or to each other. These forces, also known as force fields or attraction forces, influence human movement.

It's important to note that not all forces induce or alter motion. For a change in position to occur, the applied force must exceed both the weight of the object and any frictional forces acting upon it.

Types of forces on the body

Compression Force

• Forces are moving primarily in an approximating direction
• Compression stimulates bone, cartilage, discogenic tissue, and often neurological tissue.
• When these tissues are overloaded, this leads to fractures, in some cases disc damage, or even nerve compression.
• Examples: stress fracture of vertebrae, disc herniation, cervical radiculopathy, and compartment syndrome. Insufficient loading may lead to osteoporosis for example.

Shear Force

• Forces are NOT moving in opposite or approximating directions exclusively. This is a COMBINATION of tension and compression.
• When shear is the primary motion occuring, the body often lacks sufficient ways to attenuate this stress and may  lead to degenerative changes over time or perhaps even acute tissue rupture.
• EXAMPLES: This is seen in ACL ruptures and spondylolisthesis.

Tension Force

• Forces are oriented primarily in opposite directions
• Tension stimulates muscle, tendon, ligament and in some cases neurological tissue.
• Overload with “tension” leads to sprains, strains and in some cases peripheral nerve injury.
• Examples: hamstring tear, patellar tendonopathy, brachial plexopathy, MCL tear. Insufficient loading leads to muscle atrophy, and weak ligaments and tendons for example.

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