A: Nothing — just get out there and take your
workout to the max right away!
B: Stretch to loosen up your muscles.
C: Do some light cardio to get your heart rate
up, then stretch.
If you chose A, we're sorry to say you're mistaken. You don't want to go from zero to 60 immediately. Taking some time to warm up will get your body ready for exercise and help you prevent injuries.
But you're also wrong if you chose B. That may come as a surprise, because for years exercisers thought that stretching before the main portion of their workout was the right thing to do. Today we know that stretching before your muscles are warmed up is a no-no — stretching "cold" muscles actually increases your risk of pulling or tearing them.
The correct answer, then, is C. Start off with a little light activity for five or ten minutes to get the blood flowing. Going jogging? Warm up by walking briskly. Playing a game of basketball? Practice your layups for a few minutes first. After your muscles are warmed up, then you can stretch them. You can also stretch at the end of your workout — it feels good and provides a great cool down.