The key to minimizing injury is minimizing force. From basic physics, we learn that force equals mass times acceleration (F=ma). This is known as the acceleration law. While it is natural to be aware of the amount of resistance (mass) we use for a strength training exercise, the acceleration of movement (speed) for any activity or exercise, is almost always ignored. Acceleration refers to a change in velocity. If your body stops, slows, increases speed or changes direction, it undergoes acceleration. The amount of force the body is exposed to during movement increases or decreases in direct proportion to the speed of movement. The faster you move, the more force the body is exposed to. Even exercise using a relatively light resistance can produce injury if performed in a ballistic fashion. In reference to a strength training program, many well-meaning physicians and therapists recommend reducing the amount of weight for patients without realizing the real danger – force. In addition, most people do not know that a specific amount of weight for a strength training exercise may feel “light” or “heavy” due to gradual changes in movement speeds, slight variations in body positions while performing the exercise or minor adjustments in the design of the apparatus.

Excessive weight or resistance does not directly cause injury. People usually become injured because of their exercise behavior. For example – suppose someone wanted you to try and lift your car. Why your car?… to most people it represents an impossible amount of resistance and you will not be able to lift it. Assuming that you can obtain an effective grip, you begin to gradually and evenly apply increasing force to the car in your attempt to lift the car. You build up to a maximum force over the duration of 10 seconds, sustain this maximum force for several additional seconds, continuing to ventilate, then slowly decreasing the force and relaxing. Did you hurt your back? No! However, if you were simply commanded to lift the car – without the detailed instruction and warnings to slowly apply and let off force – the typical reaction is to yank and heave at the resistance. This behavior - not the weight of the car – commonly results in injury.

Regardless of the effectiveness or efficiency of a particular activity for producing physical improvements, if the nature of that activity is such that its performance carries a significant risk of injury, it should not be performed for exercise. The real objective of exercise is to stimulate the body to produce physical improvements, not to cause injuries. This is why efforts to decrease force while exercising are necessary to minimize the risk of injury. Part 2 of this article will provide you with practical information on how to limit the amount of force your body is exposed to during exercise. Always remember – Safety First!

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