Endurance running 'weakens bones'

Running may carry a health warning

Female endurance runners may build up their leg bones at the expense of their upper body, research suggests.

University of Wolverhampton researchers say their findings indicate runners must train their whole body - not just pound the streets.

They found that training boosted bone mineral density in the lower body - but cut it in upper body bones.

In total, 49 runners from regional athletics clubs across the UK took part in the study.

Running alone will probably put their upper body bone structure at some risk. Professor Alan Nevill

Lead researcher Professor Alan Nevill said: "While it is well known that bone density benefits from exercise and that the bone mass of the legs benefits from running, it would appear that this benefit is at the expense of bone density in the upper body.

"The findings act as a warning to female athletes that running alone will probably put their upper body bone structure at some risk."

Professor Nevill said it seemed that the repeated impact on the legs of running stimulated the bones to lay down new calcium deposits as a way to protect the lower skeleton.

However, he said calcium appeared to be diverted away from other parts of the body that were not directly affected.

The researchers found that the further the women ran, the greater the effect on their bone mass was likely to be - both in bulking up lower bones, and reducing the strength of the bones in the upper body such as the arms and ribs.

Dietary impact

The effect was more pronounced among women who consumed greater amounts of calcium.

Runners who consumed an extra 200 milligrammes of calcium a day - 25% of the recommended daily amount - were found to have a 1.3% greater mineral density in their leg bones, but a 1% lower mineral density in the lumbar region of their spine.

The research echoes a previous finding that in some cases long distance runners may actually have weaker than average bones.

The scientists who undertook that research suggested the problem was possibly that long distance runners tended to restrict their dietary intake because they thought excess weight would damage their performance.

Sam Howells, a senior sports physiologist at Lilleshall Sports Injury and Human Performance Centre, told BBC News Online that it was important that athletes exercised their whole body, and ate a healthy balanced diet.

"If you carry too much weight as a runner you tend to be at a disadvantage when compared with lighter athletes so there is a tendency to cut out high fat foods such as cheese.

"Unfortunately these type of foods are also high in calcium."

The research is published in the journal Medicine and Science in Sport and Exercise.