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Fighting back against bone loss: an aerobics pioneer says strength training can help in the fight against osteoporosis.


The importance of regular aerobic exercise is well-known and well-documented. Weight reduction, improved cardiovascular performance, improved lung function, and an overall increase in phyical and emotional well-being are jsut a few of the many benefits of a regular aerobic workout. In fact, in 1978, the American College of Sports Medicine basically equated fitness with aerobic exercise by recommending aerobic exercise three to five days per week for 15 to 60 minutes for all healthy adults. However, that recommendation made no reference to strength training.

In the last few years the benefits of strength training have been closely examined. While many considered strength training only in terms of increased muscle bulk, its benefits are now known to be far more extensive. Medical research has now proven that strength training can have an extremely beneficial effect on bone mass as well as muscle. In the past, women have often avoided strength training because of a perceived social bias against developed muscle mass in women. But the benefits for women far outweigh the social stigma because of the role that strength training may play in the prevention of osteoporosis. This is one of the reasons that the American College of Sports Medicine has just amended its 1978 recommendations to include two strength training sessions per week in addition to three to five aerobic workouts.

Osteoporosis is a disorder of the bone which currently affects some 24 million Americans. The disease causes gradual bone loss which can eventually result in bone fractures with little or no trauma. Statistically, one out of every three women in their 60's will suffer a fracture in the spine because of osteoporosis, and one out of every three women in their 70's will break her hip.

The treatment of osteoporosis remains very difficult at best. There is no question that the best approach is to prevent it, and one of the most effective means of prevention is to develop maximum bone mass prior to the onset of bone loss and then to maintain the bone to the highest degree possible. This is where the benefits of strength training on bone mass are just beginning to be realized.

The strength of the skeleton is predominantly determined by the amount of mineral in the bone, which is referred to as bone mineral density. For all practical purposes, the terms bone mass, bone density, and bone strength can be used synonymously.

Although bone is often thought of as a hard, inert substance, it actually has a life cycle of its own. During this life cycle, old bone is destroyed, then replaced. In order to increase in height during the growth years, more bone must obviously be made than is destroyed. But even after an individual reaches maximum height, density can continue to increase. Left to its own devices, bone will reach its maximum density level sometime during a person's 20s and almost certainly prior to the age of 30. There is generally no additional increase in density unless specific measures are taken to stimulate the metabolism of the bone. After age 40, a decline in bone density is often seen in both men and women, ultimately resulting in sufficient loss of density to compromise bone strength. It is at this point that fractures of the spine, hip, and wrists often occur. Frequently these occur not because of some serious accident, but simply during the course of everday activities.

While inherited factors certainly play a role in the development of maximum height and bone density, lifestyle factors such as exercise clearly influence the development of bone strength. The potential benefits of exercise on bone mass include the initial development of a higher peak bone density prior to age 30, the maintenance of any given level of bone density after the usual age of attainment of peak bone mass, and the ability to increase bone density after the usual age of attainment of peak bone mass.

Along with the many other exciting revelations from the NASA space program, the effect of weightlessness on bone mass reinforced the belief that exercise is important in the maintenance of bone strength. Using techniques which allowed scientists to measure the bone density of the astronauts of Skylab 4 both before and after space flight, it was discovered that weightlessness caused a marked loss of bone strength. In the absence of the pull of gravity, the bones were no longer required to support the weight of the body. As a consequence, the bones began to deteriorate rapidly. The calcium that was lost from the bones was eliminated from the body through the kidneys in such large amounts that there was actually concern that the astronauts might develop kiney stones in space! NASA's original plans for providing exercise for astronauts in space had centered around providing aerobic exercise to maintain cardiovascular fitness, which can easily be done in zero gravity. They are now working to devise forms of strength training that can be performed in space in order to protect the astronauts from muscle and bone deterioration.

Research on the effects of various types of exercise on the bones for those of us who are Earth-bound is also proceeding. Much of this research has been done in just the last 10 years because only recently has the sophisticated technology been developed to measure bone density. As early as 1971, however, research was published in Sweden in which the bone density of the lower leg was measured in three different groups of men: professional or world class amateur athletes, recreational athletes, and those who participated in no regular exercise at all. The types of exercise performed by these various groups included weightlifting, running, soccer, and swimming.

The findings from this early study indicate that the professional athletes and world-class amateurs had significantly stronger lower leg bones than the recreational athletes and non-exercising men. But the recreational athlete had stronger leg bone than the non-exercisers. When the effects of the different types of exercise on the leg bone were examined, the activities which produced the greatest load on the leg resulted in the stronger leg and the greater bone density. The weightlifters had the strongest leg bones, followed by the runners and soccer players, and then the swimmers. This suggested that even the modest exercise programs performed by the recreational athletes could increase bone strength, but the exercises that created the greatest load on the bone were potentially the most effective in increasing bone strength.

In support of this theory were two other early studies looking at specific types of exercise. In 1980 results were published on a group of male tennis players. The bone strength in both forearms was measured in these men. The strength of the bone in the racket arm, which had been subjected to the repetitive impact of the tennis ball hitting the racket, was much greater than that found in the non-racket arm. In the latter part of the 1980's, the technology for measuring bone strength in the spine became available, and researchers began to look at the effects of loading on this area of the skeleton. A study of power lifters in Sweden utilized this new technology to examine the effects of lifting on the spine. The study showed that the power lifters had greater bone strength in the lower spine than a similar group of men who were not power lifters.

Of course, most of us are not power lifters, nor are we world-class athletes, although we may aspire to be. There are many studies now examining the effects of recreational running and fitness regimens using resistance machines and free weights on bone strength. In a study performed by researchers at the Standford University School of Medicine in 1986, male and female runners were found to have 40% more bone mass than their non-running counterparts. In 1989, at the University of South Carolina, muscle-building exercises performed with free weights and resistance machines were shown to increase bone strength in men. In a combined study at several medical institutions in Texas in 1990, women who regularly engaged in strength training using resistance machines were able to increase their bone strenth, while the bone strength of their non-exercising peers declined. Collectively, these studies indicate that weight-bearing activities like running and strength training exercises using free weights and resistance machines can increase bone mass in both men and women in the spine, arms, and legs. Strength training exercises have a greater effect on the bone than purely weight-bearing exercise. However, the strongest bones were found in those men and women who participated in a balanced fitness program involving both aerobic and strength training exercises. The benefits were not only seen in young men and women, but increases in bone strength also were seen after such exercise programs in participants who were in their 70s!

Other studies have looked at the ability to predict bone strength from levels of physical activity in general, and aerobic fitness and muscle strength specifically. Researchers have found that increasing levels of physical activity in general is highly predictive of increased bone strength. Increased bone strength can also be predicted independently from both aerobic fitness, as measured by maximal oxygen uptake during a stress test, and muscle strength, as measured on an isokinetic dynamometer in participants ranging in age from 20 to 75.

Clearly, both aerobic and strength training exercise can increase bone strength. In the last 20 years men and women of all ages who participated in a variety of exercise regimens have been studied to determine the effects of those regimens on bone strength. As the technology that allows us to study the bones has become more sophisticated, our knowledge of the effects of exercise on the skeleton has also become more sophisticated.

While aerobic exercise has long been viewed as a means to cardiovascular fitness, it is also a means to increased bone mass and strength. Strength training, considered by some as only a means to larger muscle mass and enhanced appearance, may be the most valuable form of exercise for increasing bone mass in both men and women. As such, it becomes an extremely valuable tool in the prevention of osteoporosis and the preservation of health and quality of life.
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Author:Cooper, Kenneth H.
Publication:Saturday Evening Post
Date:Mar 1, 1991
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