Two of the most important workout variables are the number of repetitions, or "reps," per set and the amount of weight or tension used. Depending on your goals, you may want to do more reps with less weight, or the opposite. Precor equipment is designed to help you take either path or a combination of both.

Increasing muscle mass

The best range for increasing muscle mass, particularly for beginning and intermediate trainers, is six to eight. That will thicken the muscle fibers as well as build up the sarcoplasmic portion of the muscle cell, the area between the muscle fibers and the cell wall. This sarcoplasm contains water, nutrients and other cell-volumizing ingredients.

The muscles get bigger by working against a heavy resistance that forces them to fail after six to eight repetitions. By using increasingly more resistance at that rep range, you will force them to get stronger and, ultimately, bigger.

Increasing endurance

Repetition ranges have a direct relationship to the load lifted. Twelve to 15 repetitions of a light load, eight to 10 repetitions of a moderate load, and three to five repetitions of heavy loads for endurance, hypertrophy, and strength, respectively. Resistance training protocols with ranges over 15, including 20 and 30 or more repetitions per set