No one has a crystal ball and can predict who will or will not get injured from running. It was believed that running less than 20 miles per week lowered the risk of injury, but that recommendation was based on a small number of studies. Now, however, a study called a meta-analysis (a study that reviews many studies on one subject) evaluated studies of running injuries and published the following interesting results:

1. The overall incidence of lower-extremity injuries varied from 19.4% to 79.3%, thus the range is wide, which implies that it is difficult to predict who will get injured.

2. The most predominant site of injury was the knee.

3. Higher age was reported as a significant risk factor to incur running injuries in four high-quality studies, but two other high-quality studies reported that higher age was a significant protective factor, thus the evidence is conflicting and so it's not clear if running when you are older will cause or protect you from injury.

4. Increasing distance during the week does not appear to be a risk factor for injury, and in fact, in some studies, it was shown to be protective against injury. However, this may be because only strong runners increase their mileage and they may be less prone to injury. More research needs to be done before conclusions can be drawn about increasing mileage and the risk of injury.

5. Running more than 40 miles per week was a risk factor for both male and female runners to incur lower-extremity running injuries, although the risk was higher for males, perhaps because they tend to weigh more than women.

6. There appears to be no association between the use of a warm-up and lower-extremity injuries. This means that stretching beforehand may not reduce your risk of injury. This is not a surprise, as there is virtually no research to show that stretching prevents any type of injury.

7. The most common site of lower-extremity injuries was the knee (7.2% to 50.0%), followed by the lower leg (9.0% to 32.2%), the foot (5.7% to 39.3%), and the upper leg (3.4% to 38.1%). Less common sites of lower-extremity injuries were the ankle (3.9% to 16.6%) and the hip/pelvis (3.3% to 11.5%).

8. A history of previous injuries is a risk factor for running injuries. Runners with previous injuries should pay extra attention to signs of injuries, avoid overtraining (like exceeding 40 miles per week), and take time to fully recover from their injuries.

In summary, the most important findings from this research are that (1) running more than 40 miles per week is a risk factor for injury, (2) previous injury is a risk factor for future injury, and (3) the most common site of injury is the knee.

To strengthen the thigh muscles and protect the knee against injury, try straight leg raises. To do them, lie on the floor on your back, one knee bent, the other straight, hands palm-down under the buttocks to support the low back. Contract the quadriceps on the straight leg, then raise the leg to the height of the other knee. Pause one to two seconds at the top, then lower the leg but do not allow it to touch the floor. Repeat 10-15 reps, three sets. You can use ankle weights if these are very easy. Start with one pound and work up. You should always be able to do 10-15 reps. As you get stronger, you can progress to leg extensions, leg curls, leg presses, squats, and other leg exercises.

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