Process of Aging in Women: Muscular Strength and Bone Mass Density-Part VII
As we had previously written, advancing age is associated with developmental changes in body composition as well as system changes and functional changes. The vast majority of these changes occur after the age of 40. However, bone mass density (BMD) peaks between 25 to 30 years of age after which there is a decrease at an average rate of 1% per year. Muscular strength also declines following age 25, with a 10% loss from 25 to 50 years of age. During a lifetime, one could loss up to 40% of muscle mass. Sarcopenia is the age-related decrease in muscle mass associated with decreased functional capacity among very old individuals and involves decreased energy needs. Accompanying these changes in women is a decline in estrogen function from around 47 years onward.
To counteract these developmental changes, many young women start exercise programs that act as high intensity strain levels to the skeleton but which prove effective in increasing body mass density and strength levels. However, these exercises are not typically performed by older women who, at best, do exercises that are more common to daily living, such as walking and getting up from a sitting position. This type of exercise has been shown to be the least effective in bone mineral natural growth.
One of the difficulties encountered as one reads the various studies on exercise and bone mass density is the marked variation in the intervention duration coupled with the fact that bone takes 4 to 6 months to remodel. What would be the effects of a full 6 months of high intensity strength training or low intensity walking on bone mineral density, muscular strength and calcium turnover? One would expect the high level training to increase bone mass density. Such a study was carried out by Humphries et. al. on Australian women from 45 to 65 years of age who were either taking or not taking hormone replacement therapy (HRT). They were exposed to a weight (resistance) training program (high intensity intervention-weighs and stationary bike) or a walking regimen (low intensity) twice weekly for 24 weeks. Comparing the four groups of subjects, the researchers found "that short-term high intensity resistance training provides an effective means for increasing muscular strength in women between 45-65 years. The training effects on lumbar bone mass density were not apparent in the present study". So it would seem that in older women, such conditioning does not have an effect on bone mass density.
It may be that older women have to continue to exercise for a period greater than 24 weeks or engage in more than twice-weekly exercise programs if they are to increase their bone mass density. However, muscular strength may have the effect of preventing falls in certain women or help in the walking process itself. William Evan in his editorial in the Journal of Gerontology: Medical Science suggests that "among frail nursing home residents, leg muscle power is more important than strength for performing daily activities such as climbing stairs, rising from a chair and walking. Older men and women who required the use of assistive aids to perform these tasks had 42-45% less leg extension power than those who could complete these tasks without assistance. The ability to generate force rapidly is a critical component of ambulation." Power is the product of force generation and speed of muscle contraction, which come with muscle strength.
Exercise may not give one all the desired results, but it plays a very important part in keeping us healthy and active, a contributing factor to a good quality of life.
Evans,William. Editorial: Exercise Strategies Should Be Designed to Increase Muscle Power. Journal of Gerontology: Medical Sciences 2000; 55A(6): M307-M310.
Humphries B. Newton R.U., Marshall S., McBride J. et al. Effects of exercise intensity on bone density, strength and calcium turnover in older women. Medicine and Science Sports & Exercise 2000; 32(6): 1043-1050.
Go Back to Article I of Articles on Aging-Mortality risk factors
The Aging Process-Part II-Gender Difference
The Aging Process-Part III-Cellular Senescence
The Aging Process-Part IV-Biological Aging
Go to Article V of Articles on Aging-Arteriosclerosis
The Aging Process-Part VI-Aging in Males
The Aging Process-Part VIII-Infectious Disease
Process of Aging-Part IX-DHEA
The Aging Process-Part X-Skin, Skeleton and Brain
The Aging Process:-Part XI-Apotosis and the Elderly
The Aging Process-Part XII-Biomarkers for Aging
The Aging Process- Part XIII- Body Odors
FOR AN INFORMATIVE AND PERSONAL ARTICLE ON PRACTICAL SUGGESTIONS WHEN SELECTING A NURSING HOME SEE OUR ARTICLE "HOW TO SELECT A NURSING HOME".
Harold Rubin, MS, ABD, CRC, Guest Lecturer
June 20, 2000
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