Thank you very much for the useful information Sean.
Most likely a muscle knot (spasm) secondary to exercise.
Other possibility is that these can be pads of fat (one can have these normally).
This does not appear to be a lymph node as per your description.
Have rest and watchfully monitor this for any increase in size/persistance of pain.
If this get worse or increases in size, have this examined by your doctor to make sure this is not some thing serious (and i also beleive that this is not anything sinister as per your description).
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