Muscle cramp can occur for a number of reasons and they will vary with the individual (in fact for some people who suffer from muscle cramp the cause is not known!). A number of factors can increase the likelihood of muscle cramp.

1. Dehydration during exercise (where hot weather can be another contributing factor).
2. Changes in the persons musculature from minor muscle fibre tears to minor bleeding
3. Restricted circulation (e.g. tight clothing)
4. General state of health

Prevention

1. Correct warm up including stretching.
2. Adequate water and minerals. (Possibly including supplements, magnesium is a likely key nutrient).
3. Good technique in the sport/activity.

Treatment

1. Massage the affected muscle.
2. Activate the antagonist (muscles normally work in pairs, one relaxes when the other tightens and vice versa).
3. Consider applying ice.
4. Gently stretch the affected muscle.
5. Rehydrate and replace lost minerals (e.g. suitable sports drink, appropriate foods).

Long term cramp (either a single episode or repeated cramp in the same area) can result in more serious effects. Seek medical advice in these cases.