You can know if you have a sharp pain on the outside when you put the foot down. You can also tell if the muscle is straining as you try to place the foot down. The best way to stop a muscle pull is by icing it for about 15 minutes every hour. Get tips on how to stop a muscle pull at http://orthopedics.about.com/od/sprainstraintreatment/ht/muscle.htm.
If your foot hurts a lot whenever you exercise and feels "tight," you could have pulled a muscle. However, it could also be tendinitis or something else. Regardless, rest is the best medicine you can give it