When i walk briskly, the muscle on the outer leg between the ankle and calf cramps up so badly that i have to stop walking. how can i prevent this?

Cramps: Do you stretch before and after? If not that may solve your problems. A lot of people that have a vigorous brisk walk for get to stretch.

Activity modificatio: This may be either exertion all compartment syndrome, a bone stress reaction, or a tendon irritation. Aggressive pre-stretching of the area before activity is helpful as well as stretching for increased flexibility. However if pain persist, improves rapidly with rest and is accompanied by temporary tense swelling of that area then you may just have to avoid that activity and see a ortho sports doc.

Foot type?: If stretching doesn't reolve your problem, it may be caused by poor foot mechanics. Make sure your shoes are appropriate for the activity, good quality and not worn out. Shoes can be worn out without looking that way. If none of this helps see a podiatrist and get a biomechanical evaluation. A pair of orthotics may be the answer for you.

Calf cramps: Can be caused by a number of things including: poor circulation i.E intermittant claudication, dehydration, electrolyte imbalance, vitamin deficiency, faulty biomechanics....