What to Know About Tendons

Medically Reviewed by Dany Paul Baby, MD on May 04, 2022
5 min read

Your muscles and bones work together to support your movement. A tendon is what attaches muscle to bone. They link your bones and muscles and allow them to move together during activity. Tendons protect your muscles from injury and help you move your limbs freely.

Your body has tendons from head to toe. But what are tendons made of, and how do they work? Here’s all you need to know about tendons.

A tendon is a flexible, cord or rope-like connective tissue. It forms a bridge that connects your muscles to your bones. Tendons let you move the bones in your limbs while your muscles tighten or relax. They absorb the impact of your activities and protect the muscles from injury. 

You have tendons all over your body. They connect muscles to bones in your shoulder, elbow, wrist, knee, heel, and so on. The Achilles tendon in your heel is the largest one in your body. It attaches your calf muscle to the heel bone.

Tendons have different shapes and sizes based on the muscle they’re attached to. Wide and short tendons are attached to muscles for strong, forceful movements. Thin and long tendons are connected to muscles for delicate movements. 

Tendons are made of collagen, a protein found in your body, blood vessels, and nerves. A tendon looks like a rope or fiberoptic cable. It has bundles of collagen fibers covered in a sheath of connective tissue. Collagen fibers are flexible and strong, which makes the tendon resistant to impact.

A tendon has primary, secondary, and tertiary bundles of collagen fibers. The tertiary bundle is the tendon. Its structure includes:

Endotenon. The endotenon covers the primary, secondary, and tertiary bundles. It allows the fiber bundles to glide inside the tendon to aid movement.

Epitenon. The epitenon is a thin layer of connective tissue covering the entire tendon.

Paratenon. A loose layer of connective tissue outside the epitenon, the paratenon allows the tendon to move against the epitenon and the other tissues it touches. 

Sharpey fibers. These are collagen fibers that connect the tendon to the bone.

Tendon bursae. These pockets contain fluid to help reduce the friction between the tendon and surrounding bones. 

Synovial sheath. Tendons in your hand and foot have a protective outer covering called the synovial sheath. It makes synovial fluid, which is a lubricating fluid. The fluid helps the tendon move smoothly at the junction between the muscle and bone.

Tendon cells. Tendon cells include tenocytes and tenoblasts. Tenocytes are long, whereas tenoblasts are round cells with large, oval nuclei. 

When you tighten a muscle, the tendon pulls the bone attached to it. This causes movement. Tendons act as levers that move the bones when you tighten or relax your muscles. They transmit the force produced by muscle movement to the bones to allow movement and maintain body posture. 

Tendons are stiffer than muscles and are strong enough to handle a lot of weight. They’re resistant to impact caused by activities like running or jumping. But they are prone to injuries like strains or tears.

Your tendons are prone to damage because they are attached to muscles all over your body. They can get damaged due to aging, overuse, injury, or health problems like arthritis. Tendon conditions can occur as you get older. Tendons become thinner and weaker with age.

The most common tendon conditions include:

Strain. They occur if you twist, pull, or tear a tendon in your arms or legs.

Tendonitis. Here, your tendons get inflamed or swollen due to aging, too much activity, or overuse. It is also called tendinitis. Its most common types include:

  • Achilles tendonitis. It affects the Achilles tendon, which connects your calf muscle to the heel bone.
  • Patellar tendonitis. It affects the tendon connecting your kneecap or patella to your shinbone in your leg due to overuse.
  • Rotator cuff tendonitis. It affects the tendon in your shoulder muscles due to too much activity or injury.
  • Tennis elbow. When you overuse your arm muscles, the tendons around your elbow can tear. This is called tennis elbow.

Tenosynovitis. Here, you have tendonitis along with the inflammation of the synovial sheath that covers the tendon. 

There are two types of tenosynovitis — DeQuervain’s tenosynovitis and trigger finger. DeQuervain’s tenosynovitis causes swelling in the thumb tendons along the wrist to the base of the thumb. It can occur due to overuse, continuous grasping movements, or health conditions like arthritis. Trigger finger or thumb occurs when your finger or thumb gets stuck in a bent position.

Flexor tendon injury. Flexor tendons run from the arm to the wrist, palm, and fingers. They help you grasp things, bend your fingers and thumb, and make a fist. A flexor tendon injury can affect the movement of joints in your hand.

Biceps tendon injury. These injuries occur due to small tears in the bicep, shoulder, or elbow tendons due to continuous movement or injury.

Posterior tibial tendon dysfunction. The posterior tibial tendon connects your calf muscles to the bones in your foot. These tendons help you walk. Injury or overuse can cause inflammation and affect your movement. This is called posterior tibial tendon dysfunction.

Tendon tear. This occurs due to injury or overuse. The tendon may tear in the middle or separate from the bone. Here are the most common tendon tears:

  1. Achilles tendon tear. The Achilles tendon gets torn or separated from the bone it is attached to. It can occur due to sports injuries.
  2. Patellar tendon tear. The knee or patellar tendon can tear and break off a piece of bone with it due to an injury. If it is caused by conditions like tendinitis, the tear is seen in the middle of the tendon. 
  3. Rotator cuff tear. This happens when your shoulder tendons tear or separate from your upper arm bone. It can occur due to injury or overuse.

Tendinosis. This is a long-term condition. It occurs when an increasing number of collagen fibers tear in your tendons due to overuse. The tendon is weakened and its structure damaged. Tendinosis is common in the shoulder, elbow, wrist, heel, and knee.

To help reduce your risk of tendon conditions:

  • Get enough exercise for strength training and flexibility to keep your tendons healthy
  • Warm-up before exercise to strengthen your tendons
  • Stretch after exercise to relax your tendons
  • Avoid over-exerting yourself and take rest when you’re tired or stressed 
  • Avoid activity if you feel pain
  • Use the proper method, equipment, and shoes for exercise

If you feel severe pain, contact your doctor for treatment.