by NSCA's Essentials of Personal Training Second Edition
Kinetic Select June 2017
The following is an exclusive excerpt from the book NSCA's Essentials of Personal Training, Second Edition, published by Human Kinetics. All text and images provided by Human Kinetics.
It is tempting to think of the skeletal system as an inert framework comprising simply a set of levers that muscles act upon to create movement. However, bone tissue is very much “alive” and is a dynamic tissue. In addition to its role in movement and protection, bone serves as a depot for important minerals, most notably calcium. Osteoporosis is the consequence of long-term net demineralization of bone. In recent years, resistance training has been studied for its possible influence on bone mineral density (BMD). Bone tissue is significantly affected by strain; that is, deformation (bending) of bone rapidly stimulates bone cells to begin activities that stimulate bone formation (6, 65). Therefore, it seems logical to examine the effects of resistance training on bone formation, especially in the context of osteoporosis. Because osteoporosis is mainly, though not exclusively, a condition associated with postmenopausal women, most research has focused on women. Specifically, researchers have focused on the effect of resistance training on the accumulation of bone tissue prior to menopause (peak bone mass is typically achieved prior to age 40 (6), as well as on the effect of resistance training on the decline in bone mass associated with aging and menopause. Menopause is particularly critical in the development of osteoporosis because hormones like estrogen, which facilitate bone formation, markedly decline after menopause. Accumulation of bone mass prior to menopause is considered important because the greater the bone mass prior to menopause, the less severe the consequences of loss of bone mass.
The research literature has shown quite clearly that, in cross-sectional studies, stronger women tend to have thicker and stronger bones. However, selection bias may influence such studies (3). Intervention studies are less clear as to whether resistance training programs result in increases in bone mass. Some of these studies show no significant effect of resistance training on bone tissue (10, 104), while others have shown that resistance training programs can positively affect bone tissue (87, 121). Differences between studies are influenced by factors such as length and characteristics (e.g., intensity, volume, type of exercises) of the training programs, small sample sizes, differences in the extent of bone demineralization prior to training, gender, and age. A recent meta-analysis has reported that high-intensity resistance training can significantly increase lumbar spine BMD but not BMD of the femoral neck in premenopausal women (89). Nonetheless, there is enough evidence in the literature to suggest that resistance training very likely has a positive effect on bone tissue (6). What has not been examined in depth is the effect of explosive and plyometric types of training on BMD. Both strain magnitude and strain rate affect the stimulus for bone formation (6), and these would be expected to be higher with explosive and plyometric training. In addition to the obvious effects of resistance training on muscle mass and strength, resistance training may lead to decreased risk for osteoporosis, fractures, and falls in later life.
NSCA’s Essentials of Personal Training, Second Edition, is the authoritative text for personal trainers, health and fitness instructors, and other fitness professionals as well as the primary preparation source for those taking the National Strength and Conditioning Association Certified Personal Trainer® (NSCA-CPT®) exam. The book is available in bookstores everywhere, as well as online at the NSCA Store.