Tendons, also called sinews, are strong pieces of fiber that connect muscles to bones. They are similar to ligaments, which connect bones to bones. Tendons are made from collagen, and feel like tight ropes under your skin.
Achilles Tendon
The Achilles tendon connects the calf muscles to the foot. It specifically connects the gastrocnemius and soleus muscles of the back part of the leg to the calcaneus bone. You can feel this tendon just above your heel. When you tighten your calf, the Achilles tendon forces your foot down. When this tendon breaks, you are unable to do activities such as standing on your tiptoes, jumping, or other movements that involve strong downward force from the foot.
Biceps Tendon
The biceps tendon connects the upper arm muscles to the forearm and to the shoulder. It has two main parts. The upper part connects the top end of the biceps muscle to the scapula bone in the shoulder, and the lower part connects the bottom end of the biceps muscle to the radial bone in the forearm. When the upper tendon breaks, you develop pain in the front of your shoulder, but usually don't have much weakness. When the lower part of the tendon breaks, you are unable to rotate your forearm to hold your palms facing up.
Patellar Tendon
The patellar tendon connects the upper leg to the lower leg. It specifically connects the patella bone (the kneecap) to the tiba bone of the shin, so technically it is a ligament. However, people commonly call it a tendon since it serves to transmit the force of the quadriceps muscle to the tibia. You can feel this tendon just underneath your kneecap. When you tighten the quadriceps muscle in your upper leg, the patella tendon pulls your lower leg up in a kicking motion. When it breaks, you are unable to straighten your leg.
