5 on the scale is somewhat hard exercise, but it still feels OK to continue. 8 is very strenuous. A healthy person can still go on, but they really have to push themselves. It feels very heavy, and the person is very tired. 9 on the scale is an extremely strenuous exercise level. For most people this is the most strenuous exercise they have ever experienced. 10 is maximal exertion: an all-out, 100% effort. These levels accommodate differences in fitness. An unfit individual may require a level 10 effort to walk briskly uphill, whereas for a competitive athlete this may only be a level 3 effort. Over the course of the 12-week Body for Life program an individual would get noticeably fitter, so their intensity scale needs to be adjusted over time. Body for Life uses a "wave" pattern, periodically building up from level 5 to level 9 or 10 during an exercise session. This allows the muscles to warm up, and gives the body a chance to build up to a "high point" of maximal exertion. Brief but intense exercise provides maximum stimulus for the body to build strength and endurance, but without the risk of overtraining. Weight training Exercises for upper-body muscle groups include: "Pecs" (chest), e.g., bench press, pec-deck, incline fly. "Lats" (upper back), e.g., pull-down, bent-over row, dumbbell pullover. Deltoids (shoulders), e.g., upright row, shoulder press, lateral raise. Triceps (rear arms), e.g., push-down, triceps kickback, bench dip. Biceps (front arms), e.g., biceps curl, concentration curl, hammer curl. Exercises for lower-body muscle groups include: Quadriceps (front legs), e.g., squat, leg press, leg extension. Hamstrings (rear legs), e.g., leg curl, lunge, glute-ham raise. Calves e.g., standing calf raise, seated calf raise. "Abs" (torso), e.g., crunch, reverse crunch, leg raise. Most of these exercise can be performed using either dumbbells, a barbell, a Smith machine, a cable machine with adjustable pulleys or a specially-designed apparatus. Two exercises should be chosen for each muscle group. Five sets of the first exercise are performed, and then one set of the second. Weights for each set should be chosen so that the specified number of repetitions can be achieved at the specified level of intensity. For example:Weight training sessions proceed at a brisk pace, with one minute of rest between the first four sets for a muscle group, and no rest between the final two sets. The cadence for each repetition should