Neck and shoulder pain may be a result of lack of micro-movements when sitting for extended periods without moving. Ergonomic chairs typically have recline and tension controls. Small changes allow for a greater blood flow with less tightness, staving off the fatigue.
When working, change chair height, recline angle, or armrests if the body shifts. This stability, combined with some flexibility, keeps your muscles relaxed and your posture nice throughout your day.