The Latissimus Dorsi, or “lat,” is a large, flat, triangular muscle spanning the middle and lower back and attaching to the upper arm bone (humerus). It is responsible for powerful pulling motions, specifically drawing the arm down, backward, and rotating it inward. While right lat pain often stems from simple muscular causes, understanding the different origins of this discomfort is important. The pain can range from a minor, temporary strain to a sign of a deeper, more serious issue.
Acute Muscle Strain and Overuse Injuries
The most frequent source of right lat pain involves a sudden strain or tear to the muscle fibers or the connecting tendons. A strain occurs when the muscle is overstretched beyond its capacity, leading to microscopic tearing. This acute injury is typically the result of a sudden, forceful contraction or movement, such as a strong overhead throw, the explosive start of a swimming stroke, or a sudden, heavy pull during a weightlifting exercise like a pull-up or row.
Improper technique during strength training is a common trigger, especially if the lats are not adequately warmed up before strenuous activity. Symptoms of an acute strain usually include sharp, immediate pain felt in the back, side, or under the arm during the activity. The area may feel tender, and you might notice reduced strength or limited range of motion, particularly when trying to lift the arm overhead or perform pulling motions. For immediate self-care of a mild strain, resting the muscle and applying cold therapy can help reduce inflammation and pain.
Chronic Mechanical Stress and Postural Issues
Pain in the right lat can develop gradually due to chronic, low-level stress placed on the muscle over time. Sustained poor posture, such as slouching at a desk for extended periods, creates continuous, uneven tension across the muscle. This constant strain can lead to muscle imbalances and the development of myofascial trigger points, which are taut, sensitive knots within the muscle tissue.
These trigger points can cause discomfort that is localized or refer pain to other areas, such as the shoulder blade or the side of the torso. Consistently carrying a heavy bag on the right shoulder forces the lat to work harder to stabilize the trunk and arm. Underlying issues like spinal curvature abnormalities, such as scoliosis, can also place unequal tension on the right lat, resulting in a persistent, dull ache and stiffness that worsens with movement.
Referred Pain from Visceral Sources
While muscular and mechanical problems are the most common causes, pain felt in the right lat region can originate from internal organs, a phenomenon known as referred pain. This occurs because the nerve pathways for internal organs and certain muscle areas converge at the same spinal segment. The brain misinterprets the visceral signal, projecting the pain sensation to the corresponding superficial area, such as the upper back or right shoulder blade region.
Focusing specifically on the right side, the liver and gallbladder are important considerations. Conditions such as gallstones or inflammation of the gallbladder can manifest as pain in the upper right abdomen that radiates to the right shoulder or the area beneath the right shoulder blade. Similarly, issues affecting the liver can sometimes present as discomfort in the right upper back.
Referred pain may also stem from conditions affecting the diaphragm or the pleura, as these structures share nerve pathways with the shoulder and back. If the right lat pain is accompanied by symptoms like fever, nausea, vomiting, jaundice, or significant abdominal tenderness, it suggests a non-musculoskeletal cause requiring immediate medical attention. Any right-sided back pain that does not correlate with muscle activity warrants careful evaluation.
Warning Signs and Next Steps
Although most lat pain is a self-limiting muscle issue, certain accompanying symptoms act as red flags. Severe pain that does not improve with rest or that worsens significantly at night should be a concern, as this pattern is less typical of a simple mechanical strain. Pain accompanied by a fever or unexplained weight loss may suggest an underlying infection or systemic disease.
Seek urgent medical care if the pain is paired with neurological symptoms, such as numbness, tingling, or weakness that radiates down the arm or leg. Difficulty breathing, chest pressure, or loss of bowel or bladder control are also signs of an emergency requiring a trip to the emergency room. For persistent, non-emergency pain, consulting a primary care physician or a physical therapist is recommended to accurately diagnose the cause and develop a recovery plan.