Title: Elite athletes are fit but fragile
Key words: bone health, bone mass, osteoporosis, osteoporotic, fragile, peak bone mass, PBM, menopause, bone mineral density, BMD, sports physiology, mechanical stress, bone, deposition, load-bearing, exercise, osteopenia, runners, skaters, ballet dancers, rowers, tennis, athletes, post-menopausal, female athletic triad, gymnasts, weight-limited eventers, amenorrhoea, endocrine, nutritional factors, non-exercising, ovarian suppression, hypothalamic dysfunction, osteoblastic, osteoclastic, hormone replacement therapy, HRT, calcium intake, endocrine factors, muscular development, muscle, fitness, calcium, oestrogen, supplements, nutritional intake
Date: Oct 2006
Author: Morgan, G
Elite athletes are fit but fragile
Recent years has shown a growing concern over the bone health of elite female athletes leading some commentators to describe such competitors as being ‘fit but fragile’ (New et al. 2000). This review will look at the evidence which addresses these concerns.
The aetiology of osteoporosis in female athletes
Bone density and osteoporotic activity is dependent on the peak bone mass (PBM) achieved in early adulthood and age-dependent changes which, in females, become significant at the time of the menopause. PBM and the subsequent decline in bone mineral density (BMD) are dependent on genetic, endocrine, mechanical and nutritional factors. It has been said that around 50% of the PBM is dependent on genetic factors (Pocock 1987). The other three factors, however, have a significant part to play and are particularly relevant within the field of sports physiology. Woolf’s Law dictates that bone adapts to mechanical stress by becoming stronger in weight-bearing areas.
Numerous surveys have shown that prolonged inactivity leads to osteopenia and exercise leads to the deposition of new bone which is structurally stronger than its predecessor. Load-bearing exercise is most effective in this regard (Lane 1986). Surveys amongst runners, skaters, rowers ,tennis players and ballet dancers have all shown an increased BMD in women athletes (Wolman 1991, Slemenda 1993, Wolman 1990, Jones 1977, Karlsson 1993). Moreover these positive changes are seen in all age groups from children to post-menopausal women (Slemenda 1991, Recker 1992, Jonsson 1992).
Amongst vulnerable women in the post-menopausal age group even regular hill walking has been found to be beneficial, reducing the incidence of hip fracture (Pruit 1992). It appears that whilst weight-bearing exercise is beneficial in all age groups, for women involved in high intensity exercise this is not always the case. This has led to the identification of the so-called ‘female athletic triad’ which is thought to be particularly prevalent amongst female runners, gymnasts, ballet dancers and weight-limited eventers. The triad is characterised by weight loss, amenorrhoea and osteoporosis (American College of Sports Medicine 1997). In this disorder the beneficial mechanical effects of weight-bearing exercise are thought to be overridden by endocrine and nutritional factors. In this respect research has shown the following:
1. High intensity exercise leads to ovarian suppression and amenorrhoea through hypothalamic dysfunction . Amenorrhoea per se can lead to a 14% reduction in the BMD of the lumbar spine (Drinkwater 1984) in non-exercising women. The exact pathological pathway in sportwomen is uncertain as, unlike women with primary ovarian failure, such women are thought to have reduced osteoblastic activity rather than increased osteoclastic activity and do not respond as well to hormone replacement therapy (New 1998).
2. Weight loss appears to be a determinant. Amenorrhoea and diminished osteoblastic activity are associated with reduced energy intake and weight loss in athletes (Zanker 1998). An associated poor calcium intake has also been shown to be associated with amenorrhoea and osteoporosis (Myburgh 1990).
3. A lower PBM in these groups, possibly genetically associated, though dietary and endocrine factors may play a part (Keay 1997, Bennell 1997)
4. Contrary to expectations, low body weight and amenorrhoea, often seen in teenage gymnasts is not associated with osteopenia. These athletes are small and lean genetically (New et al. 2000) and the muscular development and fitness associated with this high impact sport leads to a higher PBM and BMD well into adulthood (New et al. 2000).
The treatment of osteoporosis in athletes
Female distance runners remain the most important group of elite athletes where osteoporosis may pose a clinical problem. In the light of the above it is apparent that the combination of inappropriate weight loss and amenorrhoea makes this group particularly vulnerable. Research has shown positive interactions for bone health between physical exercise, calcium and oestrogen (Specker 1996, Nieves 1998). Although oestrogen therapy has not proved very effective in treating such cases, its use in combination with calcium supplements and an improved nutritional intake offers the best hope of being able to reverse this condition.
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