Osteoporosis - female athletes distance running injuries

[mtex]

Distance running increases a woman’s risk of osteoporosis and consequent fractures, according to a new British study. London-based researchers studying 52 female endurance runners aged 18-44 found, to their surprise, a negative association between running distance and bone mineral density (BMD) in the femoral neck and lumbar spine regions.






The participants in the study, whose chosen distances ranged from 1,500m to marathon, had been exercising for an average eight hours per week at recreational to élite level, with a mean distance run per week of 32k (range 5-70k. They filled in detailed questionnaires about their training, dietary, health and menstrual habits and were subjected to a range of anthropometric tests, including bone densitometry to assess body fat percentage and BMD.

Key results were as follows:

Two of the 52 women were classified as osteoporotic at the lumber spine and one at the femoral neck. Osteopenia (bone deficiency) was diagnosed in nine and six of the participants at the lumbar spine and femoral neck respectively;
Distance run was negatively associated with lumbar spine BMD, with participants who ran longer distances appearing to have a lower BMD (lower by 1% in those running a further 10k /week);
Distance run was even more negatively associated with femoral neck BMD, which was lower by 2% in those running a further 10k/week;
Body mass (but not body fat percentage) was positively associated with BMD, suggesting that it is the lean component of body mass that is important for maintaining bone;
No significant association was found between menstrual irregularity and BMD at either site;
Although no direct relationship was found between energy intake and BMD at any site, femoral neck BMD was positively associated with magnesium intake but negatively associated with zinc intake – the latter being a surprising finding.
The researchers had worked on the hypothesis that, since physical activity has been shown to exert a positive effect on BMD in postmenopausal women, it would have an even more protective effect on younger women training much harder.

Why was this theory not borne out in practice? The researchers suggest it is probably connected with the relatively low forces applied to the limbs during running – forces which, according to previous research, are crucial to BMD.

‘Athletes involved in sports and training where forces applied to the limbs are in excess of 10 time body weight (gymnastics, weightlifting and volleyball) have been found to have higher BMD than those involved in sports where forces are only in the range of 5-10 times body weight, such as endurance running,’ they explain.

‘It seems that, although running includes many more cycles of foot strike and thus force application than these other sports, the lower loads are not as stimulatory to bone accretion. This may explain our findings that longer running distances appear to be associated with lower BMD, because the longer distances covered would be associated with lower intensity exercise and thus lower forces being applied to the limbs.’






Br J Sports Med 2003;37:67-71

Isabel Walker

Good information...thanks MTex

Actually this one needs to get saved with the Women's Articles.

[mtex]

i'll copy it there . i knew you would like this one