To be quick, you must be relaxed. Try this:
- Get into your sparring stance and guard position.
- Face a bag or an opponent.
- Move around some and then pretend you are facing a tough opponent who attacks with powerful combinations.
- Fire a few quick hand combinations.
- Now freeze, do not move or relax anything.
- Now, only relax your arms and let them drop to a hanging position. ONLY relax your arms, do not move or relax anything else.
- Now, without moving, analyze your body. How is your posture? Is your body, neck, etc. turned or twisted? How are the muscles in your neck and shoulders, are they tense? Are your back, abdominal, and leg muscles tense?
- Now relax and return to your normal posture. How much do you have to relax and move for you to regain a normal posture?
If you were relaxed in your sparring stance, practically nothing would have had to be relaxed for you to regain your normal posture. You may have had to shift your body some and stand more upright, but not much else.