A better body: additional variables in a resistance training program.

most of us have an idea of how to achieve resistance training goals with exercise choice and number of repetitions and sets. To build muscle mass, low reps at a higher weight are usually desirable; if you're looking to tone up without building bulk, more reps at a lower weight will work best. But there are other factors that influence your training regimen: namely, the order in which you perform the exercises, the number of different muscle groups targeted in one workout, and the amount of rest in between sets. These factors all influence the gains you can expect in muscle strength, size and endurance.

Order of events. Generally, the more multiple-joint exercises you can work into a routine, the more gains you will see in the above three areas (though they are less important for endurance). Expect improved motor performance, as well. Examples of these exercises include the power clean (www.biofitness.com/demo34.html) and push press (www.biofitness.com/demo39.html), which, compared to the simpler bench press and squat thrust, involve a combination of joint movements. These exercises require more skill and coordination, and should always be performed early in the routine when fatigue is minimal.

Targeting bigger or multiple muscle groups with your choice of exercise will lead to aerobic development in addition to strength. The squat, leg press, leg extension and bent-over row are all examples of large-muscle group exercises, and have been shown to consume more oxygen than exercises like the shoulder press, bench press, upright row, and arm curl. Again, always perform the bigger muscle group exercises first, working toward the smaller muscle groups. That said, the sequence of exercise for muscle endurance goals is not as crucial since it's necessary to reach fatigue in these programs, as opposed to trying to avoid it.

With these broad principles in mind, there are three major training strategies worth looking at. They are all effective ways to increase muscle fitness, but their individual differences affect how long your workouts will last and how often you'll need to perform them.

Total body workout. This routine stresses all major muscle groups, with only one to two exercises per group per session. Because individual muscle groups perform less exercises per session with this routine, train them three or more times per week. This pattern is commonly used by athletes and general fitness enthusiasts, and less so by body builders, who see the most improvements by getting muscle-specific over each session.

Upper/lower body split workout. This method exercises the upper body in one workout and the lower body in another. Because it targets and strenuously works a specific set of muscles in a given workout, it trains each major muscle group less times per week than a total body workout. Generally, the upper/lower body split workout visits the same muscles two to three times per week as opposed to three or more. It's popular across many fitness groups, including power lifters and body builders.

Muscle group split routine. With this routine you do the most exercises per muscle in one session (three to four exercises per muscle group), which means less sessions for these muscles per week (one to two). Compare this to a total body workout, which might work the same muscles only once or twice per session, but occur three to four times per week. The muscle group split routine is often used to maximize muscle size and is common among body builders.

The role of rest. For strength and power training, which relies on anaerobic energy release, heavy loads are best, with no more than six reps and long rest intervals. A maximal lift does not benefit from use of a fatigued muscle. Greater strength increases result from longer rest periods between sets, for example, two to three minutes versus 30 to 40 seconds. Multiple-joint exercises may require up to five minutes of rest. One study reported a 7% increase in squat performance after five weeks of training when three-minute rests were used--compared to only 2% gains with 30-second rest periods.

To build muscle size (as well as increase strength), use moderate to heavy loads, six to 12 reps, and rest intervals of one to two minutes. This will require a higher contribution of your energy from aerobic metabolism. Muscle endurance, however, is best achieved with a high number of repetitions (15 to 20) and minimal recovery between sets (under a minute). This forces skeletal muscle to adapt to fatigue.

Recovery days. Training with very heavy loads will increase the recovery time needed between subsequent sessions. This is especially true with multiple-joint exercises over similar muscle groups. Where heavy eccentric (lengthening) training is concerned, up to 72 hours of recovery may be needed. In lesser trained individuals, the recovery period will be longer as well. One study found that untrained women recovered only 94% of their strength after two days of rest following a five-set lower body workout of 10 reps per set (with their repetition maximum at 10). While two to three sessions per week is ideal for people just starting a weight training regimen, keep in mind that for increasing maximal strength, research points to more frequent workout sessions per week once your regimen is well under way.

(Med. Sci. Sports & Exerc., 2004, Vol. 36, No. 4, pp. 674-688)