In resistance training you exert a force against a load, whether it's your own body weight, a resistance band, a barbell or a stack of weights in a machine. Resistance training benefits your muscular and skeletal systems in multiple ways, by developing strength and muscle size, stimulating connective tissues within muscles and building and maintaining bone density.
Muscle Function
Resistance training increases the strength, power and endurance of muscles. Strength gains, especially for beginners, result in part from changes in the way the nervous system interacts with muscles. Muscles also adapt metabolically to resistance training by becoming more efficient at producing energy anaerobically, or without oxygen. To train for strength and power, focus on lifting heavier weights for fewer reps. To increase muscular endurance, lift lighter weights for more reps.
Muscle Size
Resistance training also develops larger muscles, termed hypertrophy. This growth comes from increased production of contractile proteins in existing muscle cells, or fibers. There are three types of muscle fibers, including fast and slow twitch varieties. All three may increase in size, but those known as fast-glycolytic fibers grow the most. The development of new muscle fibers may also contribute to muscle hypertrophy -- an increase in the size of muscle cells -- but the evidence for this is controversial. Training for hypertrophy typically focuses on multiple sets in the 6 to 12 rep range.
Connective Tissue
Muscles consist not only of muscle cells but also of associated connective tissue, such as fascia and tendons. These connective tissues are composed largely of a protein called collagen. Resistance training stimulates the growth of collagen, which plays a role in muscle hypertrophy and also results in stiffer, stronger tendons, although the ratio of connective tissue to muscle is not affected.
Skeletal System
Weight bearing exercise, particularly resistance training, stimulates bone development during periods of growth, such as adolescence, and helps to maintain bone mineral density throughout life. The effect is localized to the body part that is working, because bones respond to the specific strains placed upon them, a principle called Wolff's Law. To maintain bone density for adults, the American College of Sports Medicine recommends moderate intensity resistance training involving all the major muscle groups.
References
- "Exercise Physiology for Health, Fitness and Performance"; Sharon A. Plowman and Denise L. Smith; 2011
- "Exercise Physiology; Energy, Nutrition, and Human Performance"; William D. McArdle, et al.; 2007
- "Medicine & Science in Sport & Exercise"; ACSM Postition Stand: Physical Activity and Bone Health; Wendy M. Kohrt, et al.; November 2004
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