Can you describe them a bit more? Size, more about how they feel, also exactly where they are on the body. This might help with idea generation a there are lots of connective issues but not so many that would resolve with a 30min massage. One thinks of the typical presentation of "knots" in the muscle that are there with things like fibromyalgia/polymyalgia but this would perhaps be a more widespread issue in your body and would be associated with pain as well. I'd love to know the results of a muscle biopsy/Wikipedia reference-linkMRI/EMG from a neurologist as the feeling of heaviness in the legs is interesting.

A lateral thought is it might be vascular related?