If one's training objective is to reduce bodyweight, strength exercise in conjunction with endurance exercise and low-fat nutrition appears to be highly effective in this regard. In a study(22) conducted by the author, 282 adults and 116 seniors performed 25 minutes of strength exercise and 25 minutes of endurance exercise, two or three days per week. They were also given information on low-fat nutrition and asked to eat in a heart-healthy manner. After eight weeks of training, the adults gained three pounds of muscle and lost about nine pounds of fat, for a 12-pound improvement in body composition. The seniors' results were less impressive, but quite good considering they trained only two days per week and made far fewer changes in their eating habits.

In addition to increasing their muscle mass, the 398 subjects increased their muscle strength by more than 50 percent.(22) Based on research by A. Menkes et al.,(16) it is likely that these strength exercisers also increased bone mineral density. Other possible benefits from regular strength training include better blood lipid levels,(11) improved glucose metabolism,(12) accelerated gastrointestinal transit,(15) decreased back pain,(17) and reduced arthritic discomfort.(20)

Based on these and other studies, it appears that sensible strength exercise is an excellent means for improving numerous physiological factors and maintaining high levels of musculoskeletal fitness throughout adulthood. For those who have been sedentary, it is possible to reverse many of the degenerative effects associated with the aging process. Specifically, regular strength exercise can replace muscle tissue and increase metabolic rate, which is like changing from a low-powered small car to a high-powered sports car.

Recommendations for sensible strength training

Most adults have limited time and energy to give to a strength-training program. Fortunately, properly-performed strength exercise requires a relatively small time commitment. Consider the following training guidelines for safe, effective and efficient strength exercise:

Exercise. The American College of Sports Medicine recommends one exercise for each major muscle group. Major muscle groups include the quadriceps, hamstrings, lower back, abdominals, chest, upper back, shoulders, biceps, triceps and neck. Because some exercises involve more than one muscle group, eight to ten exercises are usually sufficient.

Frequency. Research indicates that beginning exercisers achieve somewhat better results with three, as opposed to two, strength-training sessions per week.(3, 23) However, two workouts per week produces about 75 percent as much strength gain and muscle development as three workouts per week. Consequently, both two-day and three-day strength-training programs are recommended depending upon personal preference.

Sets. Studies by D.B. Starkey et al.(18) and W. Westcott(23) have shown similar strength improvements for single-set and multiple-set training programs. Because it requires far less training time to perform one set than three sets per exercise, single-set strength exercise would seem preferable for practical purposes.

Resistance. Most strength authorities agree that approximately 75 percent of maximum resistance represents a safe and productive training load. This is heavy enough to stimulate high levels of strength development but light enough to pose a low risk of injury.

Repetitions. Research reveals that most individuals can complete eight to 12 controlled repetitions with 75 percent of their maximum resistance.(22) It is therefore recommended that adults typically train with eight to 12 repetitions per exercise set.

Progression. For gradual increases in the exercise resistance, it is hard to beat a double-progressive training approach. Begin with a resistance you can perform about eight times. First, increase the repetitions until you can complete 12 good repetitions. Second, increase the resistance about five percent, which will reduce the number of repetitions you can perform. Next, work up to 12 repetitions, and increase the resistance again by five percent.

Speed. There is general consensus that strength exercise should be performed with controlled movement speed. However, research(21) indicates that four-second, six-second and eight-second repetitions are equally effective for improving muscle strength. Perhaps the most common training protocol is six-second repetitions, with two seconds for the lifting movement and four seconds for the lowering movement. The longer lowering phase emphasizes the stronger negative muscle contraction, and provides an excellent strength-building stimulus.

Range. A. Jones and colleagues(13) have produced convincing research that full-range exercise movements are necessary to develop full-range muscle strength. It appears that muscle strength is specific to the movement range trained, and that best results are obtained by exercising each muscle group from the fully-stretched to the fully-contracted positions.

Technique. In addition to controlled movement speed and full movement range, exercise technique is a key training factor. To avoid unnecessary blood pressure escalation, it is important to practice continuous breathing and continuous muscle movement. That is, never hold your breath and never hold the resistance in a static position for more than a moment.

Summary

The typical aging adult experiences a gradual but substantial decrease in muscle mass and metabolic rate that contribute to a variety of degenerative problems. Thus, a sedentary lifestyle reinforces itself leading to a reduction in the quality and, perhaps, quantity of life. Regular strength training is an effective means for replacing muscle tissue, increasing metabolic rate and reversing some of the degenerative processes. Specifically, strength exercise may increase bone mineral density, improve blood lipid levels, improve glucose metabolism, accelerate gastrointestinal transit, decrease back pain and reduce arthritic discomfort.

Sensible strength-training programs are characterized by safe, effective and efficient exercise procedures. For example, it may be advisable to perform one set of exercise for each major muscle group, with a resistance that can be performed for eight to 12 repetitions. Progression should be gradual, and proper technique should ensure controlled movement speed, full movement range and continuous breathing. Two or three training sessions per week are recommended.

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Jones A., M. Pollock, J. Graves, et al. (1988). Safe, Specific Testing and Rehabilitative Exercise for the Muscles of the Lumbar Spine. Santa Barbara, Calif.: Sequoia Communications.

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Menkes, A., S. Mazel, R. Redmond, et al. (1993). Strength training increases regional bone mineral density and bone remodeling in middle-aged and older men. Journal of Applied Physiology, 74: 2478-2484.

Risch, S., N. Nowell, M. Pollock, et al. (1993). Lumbar strengthening in chronic low back pain patients. Spine, 18: 232-238.

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Tuft University Diet and Nutrition Letter (1992). An IQ test for losers. 10: 6-7 (March).

Tufts University Diet and Nutrition Letter (1994). Never too late to build up your muscle. 12: 6-7 (September).

Westcott, W. L. (1994). Exercise speed and strength development. American Fitness Quarterly, 3 (3): 20-21.

Westcott, W. L. (1995). Strength Fitness: Fourth Edition, Dubuque, Iowa: Wm. C. Brown Publishers.

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Wayne L. Westcott, Ph.D., is fitness research advisor at the South Shore YMCA in Quincy, Mass., and author of 21 books on strength training.