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Resistance training is essential to stop the progression of, or reverse, osteoporosis!

Proposition for Debate - by Karen Carmichael (Otago)

Contents

• Statement of the Topic
• Background Knowledge
• New Knowledge
• Medications and Supplements
• Clinical Implications
• Summary
• References
• Short Answer Review Questions

Statement of the Topic

Proposition for debate: Resistance training is essential to stop the progression of, or reverse, osteoporosis.

Background Knowledge

Osteoporosis is a metabolic bone disease characterized by a loss of bone mass and disturbance of bone architecture. (Katz and Sherman 1998) This leads to enhanced bone fragility and therefore an increased risk of fractures. (McCardle et al 1996, p. 797) Bone is formed from collagen, minerals and about 50% water. It is continually being remodelled. (McCardle et al 1996, p. 45). Bone is a major reservoir for serum calcium, which must be kept in a state of homeostasis. The body cannot manufacture calcium, so if enough calcium is not ingested it must be liberated from bone to maintain serum levels. If the intake of calcium is not improved, osteoporosis may result as bone is demineralized and resorbed by the osteoclasts.

Osteoporotic fractures are related primarily to bone mass, this depends heavily on peak bone mass attained (about the third decade) and the rate at which bone is lost, especially after menopause (Adami, 1994). In women bone mass decreases approximately 1% per year from age 40 through to menopause, when the protective effect of estrogen is lost. Bone loss and deterioration then accelerate markedly for about 10 years, and then level off. ( Katz and Sherman 1998) Therefore the major goals in the treatment of osteoporosis are to maximise bone mass early in adulthood and minimize bone loss later in life. (Kelley 1998)

Osteogenesis, or bone formation occurs when osteoblasts begin to lay down new bone this is then mineralised. Osteogenesis appears to occur in response to various stresses exerted on the bone.

Osteoporosis as defined by the World Health Organization (WHO): Bone density 2.5 standard deviations below the mean density for young adults (Katz and Sherman 1998)

Resistance training as defined by (Zachazewski et al 1996, p. 206), is "any form of overload resistance specifically applied to enhance and develop muscular strength, endurance and power." "Resistance, or weight-lifting exercise, is a combination of static and dynamic contractions. At the initiation of the movement, there is a static contraction until the muscle force exceeds the weight of the object to be lifted. This is followed by a dynamic concentric contraction to raise the weight, and a dynamic eccentric contraction to lower it." (McCartney 1999, p. 31

Important factors in the prevention of osteoporosis have been identified as adequate calcium intake throughout life, the protective effects of oestrogen, and exercise, specifically weight-bearing exercise, and genetics. (McCardle et al 1996) Researchers have attempted to quantify the importance of each component in the prevention or reverse of osteoporosis, but there still remains significant debate on the best means of preventing the condition.

To answer the question of whether or not resistance training is essential to stop the progression of or reverse osteoporosis, it is important to know the effects of resistance training on the skeleton.Whether resistance training is essential to increase bone mass? And what other factors may be equally or more important in maintaining bone mass.

First I will look at the effect of resistance training on the skeleton. Then the effect of impact loading and gravity dependent positions on the skeleton, and then investigate the relative importance of calcium intake, and hormone replacement therapy on osteoporosis.

New Knowledge

Resistance training

There has been a lot of work done on resistance training and bone mineral density. Wolff's Law states that stress or mechanical loading applied to the bone via the muscle and tendons has a direct effect on bone formation and remodelling (Layne and Nelson 1999).

There is a lot of evidence to support the statement that resistance training has a positive effect on bone mineral density. Male weight lifters have been shown to have greater bone mineral density (BMD) than controls in several studies reviewed by (Layne and Nelson 1999, Suominen 1993, Chilibeck et al 1995). There is however some controversy in looking at cross-sectional studies of weightlifters, because it is difficult to control for variables such as genetic make-up and the use of drugs.

There is research to suggest that the effect of resistance training is site specific. ( Kerr et al 1996, Dook et al 1997, Layne and Nelson 1999) Kerr et al (1996) looked at the effect of a one year resistance training program on the bone mass of 56 postmenopausal women.  They had two groups, one performed strength training, consisting or a 3 x 8 repetition maximum (RM) program and the other performed endurance training, or a 3 x 20 RM.  They found that the strength group had a significant increase in bone mineral density.  They also found that the changes were site specific.  Their conclusion was that the peak load is more important then the number of loading cycles in increasing bone mass in early postmenopausal women.  This would support the argument that resistance training is important in the prevention or reversal of osteoporosis.  The bone mineral content (BMC) increase was noted particularly at sites where the muscles pull, suggesting that the mechanism by which osteogenesis is stimulated is by the pull of the muscles.

Layne and Nelson (1999, p.29) found in their review that, "Research indicates that resistance training is positively associated with high BMD in both young and older adults, and that the effect of resistive exercise is relatively site specific to the working muscles and the bones to which they attach."

(Gutin and Kasper 1992) also found in an earlier review that resistance training seemed to have a stronger effect on osteogenesis than other forms of exercise.

Ryan et al (1994) looked at 21 men over 61 years old and 16 controls; they implemented a 16-week strength-training program, using weight machines, free-weights and body resistance work.  They found that they got a 2.8% increase in BMD at the femoral neck, but nowhere else.  On looking at the exercises, the leg weights were higher, and more repetitions performed, than for the arms or trunk.  So this could have some bearing on their findings. (Ryan et al 1994) They also found that an identical strength-training program can increase femoral neck BMD in older men regardless of whether baseline values of BMD are low or high, which has important implications for the treatment of osteoporosis, where they are starting off from a low baseline.

However there is some conflicting evidence that does not show a significant increase in BMD with resistance training as noted in review articles (Kelley 1998, Layne and Nelson 1999).

Kelley (1998) reviewed 11 randomised controlled trials.  In meta-analyses of the studies it suggested that exercise might slow the rate of bone loss in postmenopausal women.  However he stated that: "it would probably be a serious mistake to rely solely on exercise for preserving bone mass during the postmenopausal years." (Kelley 1998, p.82) He also found that both aerobic and resistance training increased regional BMD.  This agrees with Layne and Nelson (1999), although they noted that resistance training might have a larger effect than aerobic exercise.

It would therefore seem that resistance training does have an osteogenic effect on bone, with most positive effect seen in high loading exercises, at the areas which the muscles affected are pulling.

Impact loading

Impact loading and gravity dependent positions, also seem to have an important effect on osteogenesis and BMD.  There have been a number of studies looking at the differences in BMD between high impact loading sports, such as gymnastics and volleyball, versus sedentary controls or swimmers. (Calbert et al 1999, Cassell et al 1996, Dook et al 1997)

Calbert et al (1999) found that whole-body BMC and BMD were higher in elite male volleyball players than in the control subjects.  They state that "High mechanical impact and weight-bearing activities seem more efficient in increasing BMC and BMD than exercise which does not involve impact loading." (Calbert et al 1999, p. 468) They observed that a single game of volleyball, could involve more than 300 maximal vertical jumps per player, the athletes were also involved in weight-training to increase smash and jumping power.  So although volleyball is a high-impact sport some weight training is involved, therefore it cannot be said that the increases in BMD are purely due to high mechanical impact. In fact jumping vertically is a plyometric type exercise, which involves power and the resistance of the body weight, so this could be defined as a type of resistance exercise.

Cassell et al (1996) compared the BMD of elite 7 to 9 year old female gymnasts, swimmers, and a group of controls. They hypothesized that BMD would be higher in gymnasts, than swimmers, but that both these groups would have a higher BMD than the controls, due to the increased muscle contraction, exerting increased forces on the skeleton. However they observed that only the gymnasts had a significantly higher BMD than the controls.  They suggest that this supports other studies that have found that weight-bearing activity is necessary to produce an increase in bone mass.  It would also suggest that the resistance of water in swimming is not of a high enough load to offset the amount of time spent non-weight-bearing.

Dook et al (1997) looked at different female athletes over 40 years old who had a long history of participation in their chosen sports. They compared netball/basketball as high impact sports, running/field hockey as medium impact sports, swimming as a non-impact sport, and a control group.  They found that regional BMD was significantly higher in all exercising groups, and that the impact groups had significantly higher BMD than the control group. The high impact group had a higher total body BMD, and the high and medium impact groups had greater regional leg BMD than the swimmers and controls.

These results would seem to suggest that resistance does have an effect on BMD, but perhaps more so in the arms than legs, and that the back and legs may also need the additional effect of loading from gravity. It has also been noted that resistance exercise does not seem to have the same effect on the lumbar spine as it does on the appendicular skeleton. (Adami 1994, Ryan et al 1994)

Gravity

Gravity certainly seems to have an important role in the level of BMD as evidenced from studies conducted in space and on prolonged bed-rest.

"When the skeleton is unloaded as in space flight, bone mass is lost in weight-bearing bones. This bone loss is more localized than originally predicted and shows individual variation, ranging from none to 10.1% of pre-flight values in the spine, 1.3-11.4% in the femoral neck, and 0.4-9.5% in the tibia bone of cosmonauts after long-duration flights." (Baldwin et al 1996)

Bloomfield (1997) found that there was a significant decrease in BMD at the lumbar spine, femoral neck and calcaneus in able-bodied men after prolonged bed rest, this may not be fully reversed after 6 months of normal weight-bearing activity. She also noted that, "a dramatic increase in both urine and faecal calcium is routinely observed within one week of the onset of bed rest, reflecting an evolving negative calcium balance." (Bloomfield 1997, p.201)

It was also observed that the biggest loss in BMD occurred in the lower limb, supporting the hypothesis that gravity induced loading, is more important here than in the upper limb.

Other studies have also found that bed rest leads to a rapid and severe demineralisation with a reduction in bone mass of about 1% per week. (Ernst 1994, p.5)

Medications and Supplements

So it can be seen that resistance and weight-bearing exercise is important in maintaining BMD, but how does this compare to the "easier" method of taking medication and supplements in maintaining or reversing BMD. Katz and Sherman (1998, p.40) believe that: "Though exercise is an important part of the osteoporosis prescription, medication is also a necessary complement for almost all postmenopausal patients who have osteoporosis."

Estrogen is possibly the most widely used drug for the treatment and prevention of osteoporosis.  Estrogen therapy has been shown to preserve bone in postmenopausal females. (Ballard et al 1990, Chilibeck et al 1995, Katz and Sherman 1998) Another popular treatment is calcium supplementation.  Devine et al (1997) did a 4-year follow-up study on the long-term effect of calcium supplementation in postmenopausal women.  They concluded that: "calcium supplementation produces a sustained reduction in the rate of loss of bone density at the ankle and hip sites in elderly postmenopausal women." (Devine et al 1997, p.23) A further study showed that calcium supplementation plus exercise had less bone loss at the femoral neck site when compared with calcium supplementation alone. (Prince et al 1995, p.1068)

It may be that exercise, specifically resistance training, or high-impact exercise is needed to promote bone formation. The finding, that increasing calcium intake in prolonged bed rest studies only reduces the negative calcium balance but does not normalize it supports this idea. (Bloomfield 1997, p.202)

Clinical Implications

In sports physiotherapy we are constantly advising athletes on the most appropriate exercise regime they can do, to aid in recovery from injury and increase performance. It would seem also, that we could have a role in osteoporosis prevention, by advising our clients of the benefit of resistance training and high-impact sports on promoting increased bone mass.

We often treat middle aged and older athletes as well.  It seems especially in females that a resistance-training program working most areas of the body would be of particular benefit to this group.  If the loss of BMD after the age of 40 years, and then again after menopause could be slowed or halted with an appropriate resistance training regime, these people would be able to continue with activities and a higher quality of life for longer, without the risks associated with a loss in BMD. There are other numerous benefits of resistance training programs for elderly people, which haven't been covered here.

Occasionally we are dealing with athletes who have had a period of prolonged bed-rest or non-weight-bearing due to a more serious injury.  It is important to firstly educate these people on the effects of non-weightbearing, so they can take adequate precautions, and secondly to use a resistance training program to rebuild muscle strength, as well as bone mass.

Summary

In conclusion it can be seen from the numerous studies on resistance training and BMD, that resistance training, if done appropriately, does seem to have an important role in the treatment of osteoporosis. It would appear, that for resistance training to have the greatest effect that it should be started at an early age and carried on throughout life. As cross-sectional studies looking at athletes, especially weight lifters, show them to have a high BMD.  Another important aspect is high-impact loading, so a program of weights, along with a history of high-impact sports seems to be a good combination, in achieving peak bone mass, and thus working to prevent osteoporosis.

It appears that resistance training in people with, or at risk of osteoporosis, along with either estrogen or calcium supplementation, is important in reducing the amount of BMD loss and even reversing it to some degree. It is also worth noting that although not discussed here that an appropriate weight-training program, has been shown to significantly reduce the number of hip fractures in elderly, a side effect of osteoporosis.

So in answer to the proposal: Resistance training is essential to stop the progression of, or reverse, osteoporosis. I believe that it is. (Along with the effects of gravity, good genetics and a healthy diet and lifestyle!!!)

References

Adami S (1994)

Optimizing peak bone mass: what are the therapeutic possibilities? Osteoporosis International Suppl 1: S27-30.

Baldwin KM, White TP, Arnaud SB, Kraemer WJ, Edgerton VR, Kram R, Raab-Cullen D, and Snow CM (1996)

Musculoskeletal adaptations to weightlessness and development of effective countermeasures. Medicine and Science in Sports and Exercise 28 (10):1247-1253.

Ballard JE, McKeown BC, Graham HM, and Zinkgraf SA (1990)

The effect of high level physical activity (8.5 METs or greater) and estrogen replacement therapy upon bone mass in postmenopausal females, aged 50-68 years. International Journal of Sports Medicine 11:208-214.

Bloomfield SA (1997)

Changes in musculoskeletal structure and function with prolonged bed rest. Medicine and Science in Sports and Exercise. 29 (2):197-206.

Calbert JA, Diaz Herrera P, and Rodriguez LP (1999)

High bone mineral density in male elite professional volleyball players. Osteoporosis International 10: 468-474.

Cassell C, Benedict M, and Specker B (1996)

Bone mineral density in elite 7- to 9-yr-old female gymnasts and swimmers. Medicine and Science in Sports and Exercise. 28 (10):1243-1246.

Chilibeck PD, Sale DG, and Webber CE (1995)

Exercise and bone mineral density. Sports Medicine 19 (2):103-122.

Devine A, Dick IM, Heal SJ, Criddle RA, and Prince RL (1997)

A 4-year follow-up study of the effects of calcium supplementation on bone density in elderly postmenopausal women. Osteoporosis International 7:23-28.

Dook JE, James C, Henderson NK, and Price RI (1997)

Exercise and bone mineral density in mature female athletes. Medicine and Science in Sports and Exercise 29 (3):291-296.

Ernst E (1994)

Can exercise prevent postmenopausal osteoporosis? British Journal of Sports Medicine 28: 5-6.

Gutin B and Kasper MJ. (1992)

Can exercise play a role in osteoporosis prevention? a review. Osteoporosis International 2: 55-69.

Katz WA and Sherman C (1998)

Osteoporosis, the role of exercise in optimal management. The Physician and Sportsmedicine 26 (2):33-43.

Kelley GA (1998)

Exercise and regional bone mineral density in postmenopausal women. American Journal of Physical Medicine and Rehabilitation 77: 76-87.

Kerr D, Morton A, Dick I, and Prince R (1996)

Exercise effects on bone mass in postmenopausal women are site-specific and load-dependent. Journal of Bone and Mineral Research 11 (2):218-225.

Layne JE and Nelson ME (1999)

The effects of progressive resistance training on bone density: a review. Medicine and Science in Sports and Exercise 31 (1):25-30.

McCardle WD, Katch FI, and Katch VL (1996)

Exercise Physiology. (4th ed.) Baltimore: Williams and Wilkins

McCartney N (1999)

Acute responses to resistance training and safety. Medicine and Science in Sports and Exercise 31 (1):31-37.

Prince R, Devine A, Dick I, Criddle A, Kerr D, Kent N, Price R, and Randell A (1995)

The effects of calcium supplementation (milk powder or tablets) and exercise on bone density in postmenopausal women. Journal of Bone and Mineral Research 10 (7):1068-1075.

Ryan AS, Treuth MS, Rubin MA, Miller JP, Nicklas BJ, Landis DM, Pratley RE,Libanati CR, Gundberg CM, and Hurley BF (1994)

Effects of strength training on bone mineral density: hormonal and bone turnover relationships. Journal of Applied Physiology 77 (4):1678-1684.

Zachazewski JE, Magee DJ, and Quillen WS (1996)

Athletic Injuries and Rehabilitation. Philadelphia: W.B. Saunders Company.

Short Answer Review Questions

1. Why is osteoporosis more of a problem in females, compared to males?
2. Why is resistance training thought to be
3. What diagnostic criteria determines osteoporosis? What is the best tool to
4. measure bone mineral density?
5. What other benefits does resistance training have in the general
6. population, and in the elderly?
7. What are the differences between cortical bone and trabecular bone? Does
8. osteoporosis affect the two types of bone the same?
9. Does Hormone replacement therapy have a role to play in the
10. prevention/treatment ofosteoporosis?

Exercise Physiology Educational Resources 2000