Muscle knots in the Rhomboideus muscles (Rhomboideus major and minor) are easy to find because they’re located deep in your upper back, running between the inside border of your shoulder blade and your spine. These muscle knots typically do not cause pain elsewhere, keeping the discomfort localized as a dull, nagging ache or a deep throb directly in that area. This referred pain pattern is characterized by a persistent, heavy ache that feels as though it’s “under” the shoulder blade.