Bruising on the legs is usually caused by something striking them, but it can also be due to an underlying weakness in the blood vessels. Intense exercise, such as marathon running, cycling and contact sports, can also bring about bruising to the legs.
Bruising without obvious trauma to the legs may be due to an underlying medical disorder or a medication you are taking. If you are experiencing bruising consistently without an obvious cause, consult a physician. Seek immediate medical attention if the bruises are severe and accompanied by swelling of the leg.
Breaking Blood Vessels
Bruises are the result of blood vessels breaking says the American Academy of Orthopaedic Surgeons. This leads to blood leaking out under the skin. Most bruises are subcutaneous bruises, which occur just under the skin, but they can occur in the muscles or bones. Bone bruises are the most painful and severe of the three. In most cases, bruises disappear after two weeks, but they can take up to 30 days to totally fade.
Exercise Induced Bruising
Intense exercise that puts a lot of stress on the legs can lead to bruising, particularly if you are performing the exercise for a long period of time. The exercise weakens your muscles and blood vessels, which can eventually lead to bruising. Marathon running and the continual "pounding the pavement" is a good example of this says the National Institute for Fitness and Sport.
However, if you are bruising while performing less stressful exercises, and your legs aren't inadvertently being struck or bumping into something, you may have an underlying problem with your blood or blood vessels. In that case, exercising is just making the problem worse, leading to bruising.
Age and Medications
Aging and blood-thinning medications, such as aspirin or anticoagulants, contribute to bruising after exercising. Your blood vessels and skin thin out as you age according to Mayo Clinic, which can cause bruises when they are under the increased pressure of exercise. Medications that thin the blood have the same effect.
Deficiencies in vitamins and minerals involved in blood clotting, such as vitamin K and vitamin C, can also lead to bruising after exercise. In some cases, an underlying medical disorder that causes your blood to clot can be the culprit. The clot breaks when you are exercising, forming a bruise. In rare cases, a more serious disease, such as cancer, kidney disease or hemophilia, is to blame.
What More You Can Do
Most bruises will go away on their own without treatment. If the bruising is more severe, resting your legs and elevating them above the heart can help the blood from pooling. Wrapping the bruise with a bandage can help speed up the healing process. Over-the-counter ointments may help soothe the pain. If you have a bruise now and again as the result of intense exercise, it shouldn't be cause for concern.
However, bruising that occurs as the result of light exercise and no obvious trauma is cause for concern. If this is the case, or if the bruising is severe, consult your doctor to rule out an underlying medical problem. Discuss any medications you are taking to ensure they are not contributing to the bruising. If there is excessive swelling on your legs along with the bruising, seek immediate medical attention because you may have compartment syndrome, which requires surgical intervention to drain the excess fluids from your leg.