Pull-ups are used 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 your armpit, including those that become sore or painful during the exercise.
ACE Fitness recommends warming up before your resistance workout. Mimic the movement you're about to do without equipment. Include five to 10 minutes of dynamic stretching, marching on the spot, shoulder rolls, arm circles and jumping jacks or burpees.
Read more: 10 Exercises to Help You Conquer the Pull-Up
Teres Major Muscle
One muscle that can become injured or fatigued during a pull-up exercise includes the teres major. According to ExRx, 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 humerus, or upper arm bone.
During a pull-up, this muscle contracts to help you pull your body up on the bar, and then elongates 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.
Latissimus Dorsi Pain Causes
Another muscle that can become fatigued or injured during pull-ups and potentially cause pain in your armpits is the latissimus dorsi. According to ExRx they are the target muscles of a pull-up. These large muscle bands stem from your spinal column and insert 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.
Mild to Moderate Pain
While performing a pull-up, your back and shoulder muscles are likely to feel a minor amount of armpit lat 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.
Read more: Latissimus Dorsi Strains
Before You Pull-Up
If the Fittest Man on Earth, aka the CrossFit games champion, makes pull-ups look easy, it's because he has devoted six or seven days a week all year to training. You however, hit the gym and be honest, do not generally make pull-ups a part of your daily workout. No wonder you're getting hurt.
Ace Fitness recommends doing alternative exercises to strengthen your lats over time. Perform assisted pull-ups by placing a super band around the pull-up handles. Insert your feet or knees into the bottom loop. Straight-arm pull-downs and biceps curls will round out the exercises necessary for you to master the pull-up.