Tendon

Main thing

A tendon is a tough, flexible band of fibrous connective tissue that connects muscle to bone. Tendons transmit the mechanical force of muscle contraction to bones, allowing movement of joints and limbs. They are composed primarily of tightly packed collagen fibers arranged in a hierarchical structure, giving tendons remarkable strength to withstand the stresses of muscular contraction. Tendons are found throughout the body, from the head to the toes, with the Achilles tendon being the largest.

Terms

• Collagen: The main structural protein in tendons, providing strength and flexibility.

• Tenocytes: Mature tendon cells anchored to collagen fibers that maintain tendon structure.

• Tenoblasts: Immature tendon cells that develop into tenocytes and synthesize collagen.

• Fascicles: Bundles of collagen fibers that make up the tendon's structure.

• Endotenon: Connective tissue surrounding fascicles, allowing them to glide against each other.

• Epitenon: Outer layer of connective tissue that sheaths the entire tendon.

• Paratenon: Loose elastic tissue surrounding the epitenon, enabling tendon movement against neighboring tissues.

An analogy

A tendon is like a strong, flexible rope connecting a powerful motor (the muscle) to a lever (the bone). Just as a rope transmits the force of a motor to move a lever, the tendon transmits the force of muscle contraction to move bones and create joint motion. For example, when you pick up a heavy object, the tendons in your arm act like cables, transferring the force from your biceps muscles to your forearm bones, allowing you to bend your elbow and lift the object.

A main misconception

A common misconception is that tendons are highly elastic and stretchy. In reality, tendons are designed to be strong and resistant to stretching, unlike muscles which are more elastic. This misconception can lead to improper training or rehabilitation techniques. For instance, people might attempt to "stretch" their tendons to improve flexibility, when in fact, it's the muscles that need to be stretched. Overstretching tendons can lead to injury, as seen in cases of tendonitis or tendon ruptures in athletes who push their tendons beyond their limits.

The history

1. Ancient times (3000 BCE - 500 CE): Early understanding of tendons by Egyptian and Greek physicians, including Hippocrates.

2. 2nd century CE: Galen provides detailed descriptions of tendons and their functions.

3. 16th-17th centuries: Anatomists like Vesalius and Harvey improve understanding of tendon structure and function.

4. 19th century: Advancements in microscopy allow for more detailed study of tendon composition.

5. Early 20th century: Improved surgical techniques for tendon repair are developed.

6. 1950s-1970s: Electron microscopy reveals the ultrastructure of tendons.

7. 1980s-present: Modern imaging techniques like MRI and ultrasound enhance diagnosis of tendon injuries.

8. 21st century: Ongoing research into tendon healing, tissue engineering, and regenerative medicine for tendon repair.

Three cases how to use it right now

1. Strength training: When performing exercises like bicep curls, focus on the eccentric (lowering) phase of the movement to strengthen the tendons as well as the muscles. For example, take 3-4 seconds to lower the weight, allowing the tendon to adapt to the load and become stronger over time.

2. Injury prevention: If you're a runner, implement a gradual increase in mileage and intensity to allow your Achilles tendon to adapt. Start with a 10% increase in weekly mileage, and include exercises like heel drops to strengthen the tendon. This approach can help prevent common issues like Achilles tendinopathy.

3. Rehabilitation: If you're recovering from a tendon injury, such as tennis elbow, use eccentric exercises to promote healing. For instance, perform wrist extensions with a light weight, focusing on the lowering phase. Start with 3 sets of 15 repetitions, twice daily, gradually increasing the weight as your tendon heals and strengthens.

Interesting facts

• Tendons can withstand forces up to 8 times a person's body weight, making them one of the strongest tissues in the human body.

• The Achilles tendon, despite being the strongest tendon, is also the most frequently injured, with over 230,000 Achilles tendon injuries occurring annually in the US.

• Tendons have a unique crimped structure that allows them to elongate by up to 4% before risking damage.

• There are approximately 4,000 tendons in the adult human body.

• Tendons have a relatively low blood supply compared to muscles, which is why they often take longer to heal after injury.