How often should you apply heat therapy to a chronic sports injury?

It depends. Ice and cooling is for acute injuries or re-exacerbation of injury to reduce inflammation. Heat is used to loosen up muscles, relieve strains, and help prevent injuries such as muscle pulls. If used for this purpose then use heat prior to exercise. Heat can also be used for symptomatic relief such as for chronic low back pain. Frequency would depend on patient preference.
Both heat and ice. I seldom use heat by itself. I use heat and ice for 10 mins. Per hour with massage of any type of topical gel such as biofreeze, cryoderm, or the old standard of tiger balm. If pain persists please have the area evaluated by a physician of the lower extremity such as a podiatrist.
Before activity. Heat can be helpful in"loosening up" your injury, or to prepare for exercise. After activity, you should always ice.

Related Questions

How often do you apply heat therapy to a sports injury that is chronic?

Controversial. Often ice is best. There may be situations where one needs to loosen up an area and heat may be applied. Some deep injuries may need some heat but ice prevents swelling and releves pain. Depending on your injury and need, you should consult with a sports medicine doctor, and physical therapist with interest in your areas of injury. Read more...
Chronic sport injury. The best thing to do for chronic sports injuries is to apply heat such as a thermaband patch or massaging ben gay 30 minutes before and after. The best thing to do to prevent sports injuries is to properly stretch and drink plenty of fluids. You can also try alternating heat and cold by applying ice packs for 20 minutes after workouts then soak in warm to hot water with epsom salt for 30 minutes. Read more...