What are Tendons and What Do They Do?

Tendons are like bridges, but instead of connecting two pieces of land, they connect our muscles to our bones. Tendons are stiffer than muscles and can withstand massive loads without much change in their shape. Here, load refers to the stress the tendon experiences when we perform different movements. The structure of a tendon makes it capable of transferring the power produced by our muscles to the bones they connect to, without losing much energy; this allows us to move efficiently. Ligaments, which attach bone to bone, are different from tendons. The main job of ligaments is to help stabilize joints by holding bones together.

So how does this work when we move? Movement begins in the brain, which sends signals through the nervous system to the specific muscles responsible for the desired action. Nerves in the spinal cord send these signals to the muscles, instructing them to contract. Tendons play a pivotal role in this process, as they are the bridge between muscles and bones. When a muscle contracts, it pulls on the tendon, transmitting the force generated by the muscle to the attached bone. This action allows our joints, like our elbows and knees, to move.

Did you know that there are thousands of tendons in the body? The largest of all is the Achilles tendon. The Achilles tendon connects the calf muscle to the heel bone. This tendon attaches to two muscles that run down the back of the leg—the gastrocnemius muscle (which in Greek means the “belly” of the leg) and the soleus muscle. The two calf muscles combine to form the Achilles tendon, which attaches to the heel bone (Figure 1).

The Achilles tendon was named after the Greek hero, Achilles. In Ancient Greek mythology, Achilles’ mother dipped him into a river, called the Styx, which made his entire body invulnerable except for the part of his foot where she held him—his Achilles heel [1]. During the battle, his enemies targeted his area of vulnerability, his Achilles, with an arrow. This led to his downfall. Today the term “Achilles heel” is used to describe a point of weakness that could lead to one’s defeat—but do not worry, the Achilles tendon is a strong structure that is resilient to injury. In fact, during walking, the Achilles tendon withstands loads of around 3–4 times the weight of the entire body. This increases up to loads of up to eight times the body’s weight when we run!

What are Tendons Made of?

When we look at a tendon under a microscope, we can see that tendons are primarily made up of a substance called collagen. Collagen is a strong, white tissue. The fibers of collagen are combined closely to one another in tiny bundles, like threads in a rope. Millions of collagen bundles combine to form each tendon. A tendon’s strength is related to how thick it is and how much collagen it contains. Muscles that create powerful forces, like the quadriceps muscle on the front of the thigh, have short, thick tendons. In contrast, tendons that perform delicate movements, like the tendons in our hands, are long and thin.

Inside tendons, there are special cells called tenocytes that help with fixing and repairing the tendon after we exercise. Tenocytes make sure the tendon is ready the next time we use it. When we play a game like football, our tendons need time to rest and recover. The amount of time a tendon needs to recover depends on how much activity we perform. Athletes who engage in demanding training routines carefully plan their workouts to allow their muscles and tendons to rest and heal before their next training session.

Tendon Pain

Tendons can become painful. The most common condition that impacts tendons is called tendinopathy. Tendinopathy is the word used to describe a condition where someone reports pain coming from a tendon when performing activities that load it. For example, someone with tendinopathy of the Achilles tendon will commonly report pain when running.

Tendinopathy can affect various regions of the body, such as the ankle, knee, hip, and shoulder. The understanding of what is happening in tendinopathy has changed over time. Scientists used to think that inflammation (which they called tendinitis) was a big part of tendon injuries. But now they have learned that inflammation may not be the main cause. That is why researchers have changed the name to tendinopathy.

It is largely unknown why tendinopathy develops [2]. A common theory is that tendinopathy may occur when we repeatedly place more load through the tendon than it is used to, without giving it enough time to repair. For example, if you are used to playing football once per week and you suddenly play 4 days per week, the tendons in your legs that help you run will have little time to adapt and strengthen to get ready for the new demands. Unfortunately, we know that this simple theory does not explain all tendon injuries… we still have a lot more to learn!

Walking Up the Rehabilitation Ladder

Did you know that people can recover from most tendon injuries by performing specific exercises? This is called rehabilitation. Rehabilitation for tendon injuries is like climbing a ladder. Different types of exercises put different amounts of weight on the tendons (Figure 2). In rehabilitation, patients start with easy exercises in which their muscles work without moving much. We call these isometric exercises, and they are gentle on the tendons. Then, patients move on to exercises in which they slowly move their joints, which puts more load on their tendons. Finally, patients can do faster movements, like skipping or sprinting, which put a lot of load on their tendons. Rehabilitation gradually makes tendons more robust.

Rehabilitation Story

Here is a story that helped guide how we treat tendon injuries today. Once upon a time, there was a doctor who loved to run, but he injured his Achilles tendon [4]. We will call him Dr. A. Dr. A did not want to have surgery to repair his tendon due to the long recovery required, so he sought alternative treatment.

At this time, there were whisperings of a new treatment. It was an exercise program that involved doing something called “heel drops.” This exercise required Dr. A to place his foot on the edge of a step, lift onto his toes, and then slowly lower downwards. Dr. A was skeptical of such a strange approach. However, he persisted with this exercise program. Guess what? Dr. A started feeling better. His pain started to improve, and before long, he could run again.

Dr. A’s story helped us learn how to treat tendon injuries. We now know that exercise can be a great way to help treat our tendons and get back to doing the things we enjoy—just like Dr. A with his running.

Nowadays, rehabilitation exercises have become the main treatment for tendon pain. The good news is that these exercises have become less time consuming over time. Health professionals like physiotherapists, who are experts in treating injuries to tendons, muscles, and joints, often prescribe these exercises.

Conclusion

Tendons are like strong ropes with the special job of passing on the power developed from our muscles to our bones, which helps us move. The strong structure of tendons structure means that they do not easily change their shape, which helps our bodies work efficiently.

When people have injured tendons, they often need to do exercises as part of a rehabilitation program. The goal of rehabilitation is to match the exercises to the person’s lifestyle, so that they can do all the activities they enjoy in their daily lives. Whether it is running a marathon or walking a dog, physiotherapists want to make sure people’s tendons are ready and strong enough to handle any activity they want to perform. So, spread the news: exercise strengthens our tendons! Just remember to progress slowly, to give your tendons time to adapt and keep up.

Glossary

Tendon: ↑ A tough “rope” of collagen and cells that connects our muscles to our bones, to help us move by letting our muscles pull on our bones.

Ligaments: ↑ Thick bands of tissue that help stabilize bones to each other.

Collagen: ↑ A thread-like structural protein crucial to maintaining the strength of a tendon.

Tenocytes: ↑ Specialized cells that are found in tendons that play a role in maintaining and repairing tendons.

Tendinopathy: ↑ Describes a tendon that hurts when we perform activities that place load on it.

Inflammation: ↑ A protective response in which our bodies send cells, chemicals, and extra blood to the affected area to help repair any damage, causing redness, swelling, and warmth.

Rehabilitation: ↑ The process of performing exercise to improve your ability to function after an injury.

Physiotherapists: ↑ Healthcare professionals who work with people to improve their function, manage pain, and recover from injuries or disabilities.

Conflict of Interest

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.