There are two common reasons that may explain why your left Achilles tendon hurts first thing in the morning -- injury or positioning. If you participate in sports or are physically very active, you may have an overuse tendinopathy -- a condition that causes micro-tearing of fibers in the tendon. While you sleep, your ankle is relaxed, placing your calf muscles in a shortened position. Standing up places a stretch on these muscles, which may cause pain in your Achilles tendon.
Your Achilles tendon is a band of connective tissue that joins your heel bone to the two major muscles in your calf used 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.
Any activity that puts stress on your Achilles tendon, such as running or jumping, can cause injury. Tight calf muscles or a sudden increase in the amount or intensity of exercise can lead to Achilles tendinopathy. Exercising with improper shoes or running on uneven surfaces can increase your risk of this condition.
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.
Rest your foot and ankle and avoid unnecessary movement if you have pain in your Achilles tendon. Make an appointment to see your doctor for a definite diagnosis if the pain lasts more than 1 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.