Not all exercise created equal.

A good exercise program should include regular, sustained, cardiovascular effort, as well as maintain range of movement, muscular strength, and balance. As a runner, you have the cardiovascular element covered. As to the rest, there are many ways to cover the bases depending on your fitness level but some exercises can cause harm. It is not always easy to know what is safe, especially when some exercises can be fine for one person, but damaging for another. Without a full time trainer by your side, how can you recognize what not to do? The President's Council on Physical Fitness and Sports has provided guidelines.

While all joints are subject to the same principles, the spine and the knees are particularly sensitive to repetitive stress, and certain exercises are notoriously risky and probably should be avoided. In general, if movements go beyond the normal range of motion there is the risk of repetitive microtrauma. Uncontrolled, ballistic movements at the end of the range of motion, will stress the joints and cause undetected damage to connective tissues. Repeated over time this will eventually cause serious damage that is felt as pain and can lead to osteoarthritis.

* The Yoga Plough--This exercise is done lying on your back and extending the legs overhead and back behind the head and neck. It is done to stretch the lower back but causes an extreme forward bend of the neck while the neck is bearing the weight of the body (as the legs pass over the head).

* Neck Hyperextension--Known as whiplash in some circumstances, bending the neck back may be safe if done slowly and with control. When done with speed and force, as in certain dance moves, this movement can be harmful.

* Hip joint Flexion--Whether you are reaching your toes from a standing position or a sitting position, this exercise can be a problem if your hamstrings are tight, or if the exercise is done repeatedly or forcefully. Only if you have very good hip flexibility, will the movement stretch the hamstring muscles. If you have tight hamstrings, stress is transferred to the spine.

* Full Sit Ups--There has been a lot of criticism hoisted at the lowly sit-up, but recent research supports the claim that full sit ups can place high amounts of compressive farce on the inter-vertebral discs. It is better to stick with partial sit ups or crunch for the upper abdominals. If the upper body is raised beyond the range of a crunch, the hip flexors are targeted more than the abdominals anyway.

* Standing Quadriceps/Hip Flexor Stretch--Reaching back while standing and holding the ankle, so that the knee is pointing straight down, fully flexed. This is an exercise all runners seem to love and when done correctly, it is reasonably safe. It is an easy mistake, though, to pull the leg outward laterally while performing this exercise--this puts stress on the medial structures of the knee, including the medial meniscus. Although there are other safer ways to stretch the quadriceps, the exercise can be done more safely if you grab the ankle with the opposite hand, which will keep the knee in a straight down position.

* Hurdler Stretch--Another exercise that is a favorite of many runners, the hurdler stretch can stretch either the hamstrings by leaning forward or the quadriceps by leaning back. Leaning forward in this position puts excessive stress on the knee. And leaning back puts excessive stress on the lumbar spine. Better to avoid this altogether and place the foot in front, against the inside of the knee and just use it to stretch the hamstrings.

Almost any exercise can be harmful if done improperly, with momentum and repetition. Understanding a few simple principles helps you evaluate not only an exercise, but also your own technique.

(This information was adapted from the President's Council on Physical Fitness and Sports, Research Digest, Series 3, No. 8. You can obtain a copy by calling 202-690-9000)

RELATED ARTICLE: When choosing an exercise, be sure that it is appropriate for you that means doing it will help you; achieve a fitness goal and that you can do the exercise in a safe manner. The microtrauma that can occur from repeatedly doing exercises that are unsafe for you can have long-term health and injury consequences.

Wendell Liemohn, Ph.D.