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How to work out a shoulder knot 
Do some light stretching. 
Muscle knots are basically chronic muscle strains caused by repetitive movements or postures that contract muscle fibers for long periods of time. Muscles are meant to contract for short durations, then completely relax.
However, performing similar movements over and over (due to athletics, weightlifting, cleaning the house, etc. ) or sustaining certain postures while at work strains muscles fibers and causes them to remain contracted.