Because of the large collection of lymph nodes, hair follicles and sweat glands found in the hollow created by your chest wall, muscles and shoulder bones, any number of things can cause pain in the armpit. A pulled muscle is one of the more benign causes. There isn't a specific armpit muscle, so the strained muscle causing your pain is likely your pectoral, triceps or latissmus dorsi. Treatment for muscle strain in the armpit depends on the severity of the injury.
Muscle Strains Explained
Your muscles are composed of many individual muscle fibers that have a fixed capacity for lengthening. When you make a movement that stretches the muscle fibers past their natural range of motion, this can create tears in the fibers.
Any movement that causes the pecs, lats or triceps to become overstretched can cause an injury that leads to pain in the armpit. It can happen from a fall or from overdoing it at the gym. Sprains are acute injuries, so most likely you will remember the event that occurred. You may have felt a mild but sharp or severe pain. You may have even heard a popping sound.
Grades of Muscle Pulls
Muscle pulls vary in severity, based on the symptoms. Knowing how severe your muscle strain is will help you determine the best treatment and whether you need to visit your doctor.
Grade I strains are mild, involving only slight damage to the muscle fibers. The soreness may be uncomfortable, but it doesn't prevent you from carrying out your daily activities — although it may keep you from doing certain types of exercises.
Grade II strains are moderate injuries in which more muscle fibers are affected. The pain is likely more severe and you may have swelling or even bruising. You may also notice some muscle weakness when using your arm. Completing everyday activities could be more difficult, and exercise involving the upper body might be painful.
Grade III strains are severe and involve a muscle separating in two or detaching from the ligament that connects it to bone. You may have heard a popping noise at the time of the injury, indicating this rupture. The pain, swelling and bruising are severe, and there is a complete loss of muscle function. Daily activities and exercise are difficult or impossible.
Getting the Right Treatment
Based on the category descriptions, you should have a pretty good idea of the severity of your injury, so you can now determine how to treat it.
Grade I Injury Treatment. If the muscle strain in your armpit is a grade I injury, you can treat it at home using the gold standard RICE protocol. This method is most effective when initiated as soon as possible after injury and continued for 48 to 72 hours:
- Rest. Cease the activity that led to your injury and avoid any activities that place stress on the sore underarm for at least 72 hours.
- Ice. Apply an ice pack for 10 to 20 minutes on the hour, as often as possible. Ice constricts the blood vessels to stop blood flow to the injured muscle, reducing swelling and bruising.
- Compression. Wrap an elastic bandage snugly around your shoulder and through the armpit. Applying compression also helps reduce swelling and can provide support to a weakened muscle.
- Elevation. Keeping the armpit at or above the level of the heart will help reduce blood flow to the injured area. Because of the positioning of the armpit and the heart, this doesn't take much "doing."
Be consistent with this treatment for the next two to three days. Doing so can reduce the pain and swelling, as well as the recovery time.
Grades II and III Treatment. You should have moderate and severe muscle strains checked out by a doctor, who will determine the scope of your injury by doing any or all of the following:
- Asking how the strain occurred
- Asking if you heard a pop at the time of injury
- Examining the strained muscle
- Asking you to perform physical tests, such as raising your arm, to determine muscle function
- Ordering X-rays or magnetic resonance imaging if a physical exam does not provide enough information
If your armpit muscle strain turns out to be a grade II injury, your doctor will likely send you home with instructions to carry out the RICE treatment. She may recommend immobilizing the arm to protect it from further injury. She may also recommend over-the-counter pain relievers or provide a prescription, if necessary.
Grade III injuries will require more comprehensive treatment, so your doctor will likely refer you to a specialist. Some complete muscle tears can be treated with immobilization via slings or casts; others may require surgery. Other treatments for pulled muscles include massage, ultrasound and dry needling.
Time to Recover
Your path to recovery will depend on which course of treatment you receive. Grade I strains may resolve within a few weeks. Until that time, you should avoid strenuous activity involving the chest, lats and arms on the injured side. Don't pick up anything heavy or reach for something above your head and avoid exercises that use those muscles.
For grade II and III strains, follow your doctor's orders. According to Harvard Health Publishing, moderate strains can take two to three months to heal, while severe strains requiring surgery can take several months. During this time, you will need to limit your activities to only those that your doctor and physical therapist say are safe.
Rehabilitation Exercises for a Pulled Armpit Muscle
At a certain point, all grades of muscle strain benefit from strengthening, flexibility and mobility exercises. Depending on the muscle that was strained, your pecs, lats or triceps will likely lose some strength and range of motion while you are recovering, even if your strain is only mild.
If you had a grade II or III strain, your doctor will tell you when you should start exercising. You may be working with a physical therapist, who will design a program for you.
If your muscle sprain was mild and you are treating it at home, you can start to perform some exercises once the pain and swelling are no longer present:
- Chest doorway stretch. Stand in a doorway and raise your arm to shoulder height. Bend your elbow to 90 degrees and press your forearm against the door frame. Rotate your chest and hips away from your arm until you feel a stretch.
- Thoracic extension. Sit in a chair and bring both hands behind your head, elbows pointing out. Press gently against the back of the head while arching your spine and pushing your elbows out until you feel a stretch.
- Triceps stretch. Stand or sit upright. Raise your arm, bend your elbow and place your palm against your middle upper back. Grasp the elbow with the opposite hand and push down gently.
- Arm circles. Reach your arms out to the side and make small circular motions. Gradually widen the circles until you are reaching your full range of motion; then switch directions.
- Isometric chest/triceps press. Press your palms together at the center of your chest with your elbows at the same height as your hands. Press your palms together, focusing on the contraction in your chest and triceps muscles.
- Scapular retraction. Stand tall with your arms at your side. Roll your shoulders back and down and squeeze your shoulder blades together.
Perform each of these exercises for three sets of 30 seconds each once or twice each day. Stop if you feel any sharp pain and avoid overstretching the injured muscle. When you return to your normal exercise activities, be conservative about increasing the intensity and load.