Pull-ups are an effective exercise to use in order to strengthen your arms, back and shoulder muscles. While you can experience a certain level of soreness after completing a strenuous exercise such as pull-ups, sharp or radiating pain in your armpits could be a sign of an injury caused by improper exercise form. Muscles that are worked during a pull-up can wrap around your arm and under you armpit, including those that become sore or painful during the exercise.
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One muscle that can become injured or fatigued during a pull-up exercise includes the teres major. According to OrthoBullets.com, your teres major muscle is a thin yet strong muscle that runs from the bottom of your shoulder blade and inserts into the upper portion of your humerous, or upper arm bone. During a pull-up, this muscle contracts to help you pull your body up on the bar, and then elogates to help lower your body back to starting position. An injury or strain in this muscle will cause pain in your back and under your arms.
Another muscle that can become fatigued or injured during pull-ups and potentially cause pain in your armpits is the latissimus dorsi. According to the FitStep website, this large muscle band stems from your spinal column and inserts just below your rib cage in the front of your body. Muscle fibers in this area also run underneath the arm and through the bottom of the armpit. When lowering yourself from a pull-up, this muscle will act as a stabilizer to your core and can become fatigued after many repetitions.
While performing a pull-up, your back and shoulder muscles are likely to feel a minor amount of pain as lactic acid builds in your body after repeated body lifting. This pain can be considered normal as long as it remains mild to moderate in severity. If you begin to feel sharp or intense pain in your armpits, back, or shoulders, stop exercising immediately and seek medical attention as this may be a sign of muscle rupture or a severe sprain.
If the pain in your armpits is too severe to continue exercising, rest your body and begin icing your painful muscle area with a cold compress or ice wrapped in a towel. According to the Pain Clinic website, severe pain can also be treated with pain medications, stretching techniques or compression treatment.