What Are Tendons?
Hello guys -
We can walk for hours at a time, but we can only do push ups for about a minute or so before wearing out.
Why is that?
Well, a big part is our tendons. In humans, the Achilles tendon is the largest and thickest tendon in the whole body. And it helps our leg muscles propel us forward when walking without having to use much energy.
In contrast, the tendons used in a push-up, such as the triceps brachii tendon, pectoralis major tendon, and rotator cuff tendons, are much smaller than the Achilles and therefore helps us much less during push-ups than our Achilles does during walking.
Long story short, tendons do a lot of work in our bodies, even though muscles get most of the credit.
As part of our continuing education here at Strength School, we are currently reading Jake Turra’s new book, succinctly called Tendon Book. Here is my summary of Chapter One:
Tendons are a type of tissue composing the body, like muscles, ligaments, and bones. More specifically, tendons are a type of connective tissue; tendons connect muscle to bone. Bones are necessary to stabilize the body as it moves, and muscles are necessary for moving bones. Muscles contract to pull on bones to produce movement, but, since bones are stiff, a stretchy muscle cannot directly connect to bone. Tendons, which are both bone- and muscle-like, facilitate this bone-muscle connection. Some muscles also contain intramuscular tendons, which increase the surface area in which a muscle can apply force. Aponeuroses are also tendons that are broad and organized in flat sheets, like the plantar fascia on the bottom of the foot.
In addition to acting as a muscle-bone connector, tendons also recycle energy. Moving a body requires muscles to expend energy by stretching and contracting. These muscle actions have a high metabolic cost (i.e., uses a lot of ATP); in contrast, tendons can stretch and recoil at no expense while the muscle remains in isometric contraction. Another function of tendons is to amplify power. When a tendon is stretched and pulled on by the force of a muscle—such as how the patellar tendon is elongated over the knee joint and pulled on by the quadriceps when the knee is bent—elastic energy is stored. When the tendon returns to its resting state, that energy is released (e.g., the body is driven up after squatting for a vertical jump).
Like muscles, tendons can transmit force. They can do so by stretching and recoiling, as demonstrated by their ability to amplify power, or via “pure force transmission.” In the latter case, a tendon remains rigid and acts as a joint stabilizer while transmitting force from muscle to bone. For instance, the elbow tendons stabilize the elbow joint and send force from the forearm muscles to the bones while swinging a golf club. Lastly, tendons buffer energy. During deceleration, muscles stop bones from moving by undergoing eccentric stress. This stress can damage muscles, so tendons reduce muscular effort by stretching first and absorbing the energy before slowly releasing it to the muscles. An example of this buffering effect is when tendons stretch as a person lands a jump. Tendons, unlike muscles, can stretch quickly and at no energetic cost since the tendon is stiffer. To summarize, the five primary purposes of tendons are to connect muscle and bone, to conserve energy, to amplify power, to transmit force, and to buffer energy.
