There are two common reasons that may explain why your left Achilles tendon hurts first thing in the morning. If you participate in sports or are physically very active, you may have “overuse tendinopathy,” a condition that results from the extra weight your foot bears when you get an unusual amount of exercise. There is no particular significance when only your left Achilles tendon hurts. Tendinopathy can occur in your left or right Achilles tendon and sometimes affects both. You feel the pain in your Achilles tendon in the morning because it is the first and only major tendon in your body that goes through full range of motion as you wake up.
Anatomy
Your Achilles tendon is a band of connective tissues that joins your heel bone to the two major muscles in your calf that are important for walking and running. These calf muscles, known as the gastrocnemius and the soleus, generate the power your foot needs to push off and take a step or rise up on your toes, such as when you are jumping.
Causes
Any activity that puts stress on your Achilles tendon, such as running or jumping, can result in a tear, injury or inflammation known as tendinopathy, tendinosis or tendonitis. Tight calf muscles or a sudden increase in the amount or intensity of exercise can lead to Achilles tendinopathy. If you are middle-aged or older, the pain may be due to arthritis or a bony growth known as a heel spur that can irritate your Achilles tendon. If you are older, you are also more susceptible to developing Achilles tendinopathy because your tendons are less flexible and more easily injured than when you were younger.
Symptoms
Your Achilles tendon may feel especially stiff and painful right after you wake up in the morning or after any long period of inactivity. You may also feel pain in your heel and up along the tendon as you walk or run later in the day. It may be especially painful if you walk up stairs or on an incline. You may feel swelling and warmth in the area due to inflammation, and your Achilles tendon may be painful to the touch.
Treatment
The first thing you should do when your Achilles tendon hurts is rest your foot and ankle and avoid unnecessary movement, according to Washington University School of Medicine in St. Louis. Make an appointment to see your doctor for a definite diagnosis if the pain lasts more than a week. Your doctor may recommend further treatment, such as ice packs, exercise or medication, depending on the cause of pain. In some extreme cases, surgery may be necessary.
