Being a marathon runner and also a sports medicine specialist, I shall look at perhaps one of the most common questions asked by runners and patients alike. "Is running bad for the knees?" This is the question I have been often asked.

As a general rule of exercise, running and walking do no damage to the knees nor will it cause arthritis of the knee when you grow old. Studies done on marathon runners have shown no evidence of degeneration or arthritis of the knees as a result of long distance running.

However, there are exceptions to this finding:

• When a runner has a previous knee injury;
  
• When a runner has an established disease in the knee joint such as arthritis, runner's knee, meniscus injury, ligament tear and unstable knees;
  
• When the exercise is excessive (long hours and high mileage). The risk here is probably not from running itself but more from the failure to notice the injury; and
  
• When the exercise has a component of speed with the knee in flexion and rotation (rugby, football, basketball, taekwondo) and is a type that has a high injury risk.

Case of a runner with knee pain
To make it easier for readers to understand my stand about running and knee injuries, let me bring up the case of this runner. Mr Singh, who had taken up running for the past year, was worried about his knees which had been aching for the past two months.

Before he took up running, he already had an old knee injury. He normally runs about 4km, three times a week at the Subang Jaya Lake.

Three months ago, he decided to run a half marathon and increased the frequency of his run to six days a week. Sometimes, he ran as much as 10km. His initial aches and pains were interpreted as normal soreness after exercise.

Check the damage
It is not entirely true that people who have knee injuries should not run. If the injury has healed, you can return to running. The amount of running you can do depends on your recovery and the previous degree of knee degeneration or arthritis. It is better to get a doctor or sports medicine specialist to check your knee condition before you return to running.

In the case of Mr Singh, his knees had already suffered some damage and X-rays had revealed a mild degree of osteoarthritis. Thus, he will face the risk of more pain and possible more injury should he continue his present form of training and long distance runs.

The anatomy of his knees had already been altered as a result of his old football injury. His knees will no longer function as well as before. He can no longer put abnormal loads and stress on his knee joints, cartilage and meniscus.

He can bend his knees but he should not put too much weight on them. Running is a weight-bearing exercise and has considerable impact on the knee joints. One kg of body weight is equivalent to 3 kg of pressure on the knee joints. This pressure could further damage the cartilage and meniscus of the joints and aggravate arthritis. The end result could be damaged knee joints and the possibility of a knee replacement.

Sports less likely to harm the knees
There are non-weight bearing sports such as swimming and cycling which place less stress on the knees. Water aerobic classes, water running and exercises using resistance machines are good alternatives for burning fat and reducing weight.

If you want to pursue sports which may aggravate your knee problems, seek medical advice. You should also wear a knee brace to give your joints more support, do proper warm-up and stretching before exercising.

Running won't hurt the knees. Many veteran runners, who have been running the 42km event and training for marathons, will agree with me. In my opinion, the benefits of running outweighs the risk of injury to the knee.

Questions to Dr William Chan can be directed to him at his e-mail spinesportmed@yahoo.com. His contact number is 012-2521 898 or 03-5635 5113.