I'm 39, male, approx 178cm in height, 72kg weight. take Sertraline, and I don't smoke. No other medical issues.
When I tense some muscles at the back of my neck above my shoulders, I only seem to be able to tense them on one side. The other side doesn't do anything. I've included a photo of the muscle I mean below.
Is this normal? Any idea what might be causing it?