The most common cause of upper back muscle pain is the muscle sprain or strain type of injury suffered by amateur athletes, part-time gardeners, and other active individuals.
People who don't take the time to train regularly, but still participate in vigorous physical activities, are the most affected. These types of injuries rarely lead to chronic back pain.
Train Consistently, Warmup Appropriately
Anyone who doesn't train consistently, doesn't do appropriate stretches and warm up exercises, and then spends the weekend at any vigorous physical activity, is susceptible to this type of injury.
This will often affect the trapezius and rhomboid muscle groups of the upper back.
Another type of back muscle pain is myofascial pain. Most muscles are enclosed in a sheath of connective tissue called fascia.
This envelope around the muscle allows it to slide past other muscles during motion, and it helps to form the tendons that connect muscles to bones.
Poor posture may also cause upper back pain. If you spend long hours at home or at work, hunched over a desk, or standing looking down at your work, this can put excessive strain on the muscles of the upper back, and over time this can lead to chronic back pain.
"may be perceived as muscle pain"
Other conditions, that may cause pain that is not really muscle pain, but may be perceived as muscle pain are lung cancer, compression fractures, and shingles.
From Your Lungs
Upper back pain from your lungs may occur when a tumor puts pressure on the nerves, or by growing directly into the spine.
Lung cancer can also cause upper back pain by spreading metastatic disease to the spine. More about lung cancer and back pain can be found at Your Lungs And Back Pain.
Vertebral compression fractures can occur suddenly, causing the sudden onset of severe back pain.
They may also develop gradually at multiple vertebrae in the upper back, causing the dowager's hump, often seen in elderly women.
Shingles or herpes zoster is a virus that resides within the nerves, often for decades. After lying dormant, often for decades, it can become active causing back pain that many people mistake for muscle pain.
Burning Stinging Pain
If your back pain has a burning and stinging, or a needles and pins tingling, kind of quality, you may have shingles.
You can learn more about compression fractures and shingles at Back and Abdominal Pain.