Interesting re the DOMS soreness. Most bodybuilders don't get sore after a while. Maybe that is why they don't grow much, either? I have advocated keeping the muscles quite sore to grow rapidly. Whether this has a side effect later on I rather doubt it. The soreness eventually evaporates until another stressful episode occurs. That could be a workout or something like climbing a hill.
If you get DOMS from merely tensing your muscles for a few minutes that is crazy. Think back to when you started lifting weights. Did you get sore after training then?