For a long time, exercise was "dispensed" or given out by coaches, athletic trainers, and physical therapists, in one simple formula. Everyone started with one set of 10 repetitions and then built up to three sets of 10 reps. At that point, weight could be added for a better workout or more repetitions were done.

Today, thanks to many new studies, this formula is being replaced. Exercises are becoming more specific as scientists learn how muscles work normally. Not all muscles work in the same way and not all conditions or diseases affect the body the same way.

Prescriptive exercise is an idea that is gaining in many circles. Exercises are given to patients based on what we know about muscles in general and what we know about diseases.

For example, low back pain is a common problem. Scientists have shown that low back muscles fatigue easily and bring on this condition. Electromyograhic (EMG) studies of the low back muscles show that only 55 per cent of the muscle fibers are firing during maximal exercise.

After that, the body "derecruits" low back muscle fibers. Other muscles are called upon instead. These "recruits" include the hip and leg muscles. Researchers suggest that repetitions beyond 55 per cent of maximal fatigue won’t result in increased muscle activity in the low back. More information is needed before we know exactly what to prescribe instead.