Exercise that puts greater strain on bones, like running, may improve long-term bone health more effectively than non weight-bearing activities such as cycling, a new study has found.
Previous research found that cyclists racing in ultra-endurance conditions suffered chronic bone resorption - where calcium from bone is released into the blood stream, weakening bones.
In the new study, researchers from Istituto Ortopedico Galeazzi in Italy set to find out whether a similar group of elite athletes - mountain ultra-marathon runners - had the same response.
Researchers measured two vital bone constituents as well as hormones associated with energy regulation. Osteocalcin and P1NP are two proteins associated with bone formation and their levels in blood are an indicator of bone health.
Glucagon, leptin and insulin are hormones involved in regulating metabolism and indicate the body's energy needs, researchers said.
Increasing glucagon levels indicate an energy demand, whilst increasing insulin and leptin levels indicate adequate or excessive energy levels, they said.
Researchers measured these three hormones as well as levels of osteocalcin and P1NP in 17 trained runners before and after a 65 kilometres mountain ultramarathon run.
They compared the levels to the hormones and bone constituents of 12 adults of the same age who did not run the race but did low to moderate physical exercise.
Compared to the control group, ultramarathon runners had higher levels of glucagon and lower levels of leptin and insulin when finishing the race, researchers said.
The falling levels of insulin within this group were linked to similarly falling levels of both osteocalcin and P1NP - suggesting that athletes may be diverting energy from bone formation to power the high-energy demands of their metabolism, they said.
However, ultramarathon runners had higher P1NP levels at rest compared to controls, suggesting that they may divert energy from bones during racing but have a net gain in bone health in the long-term, researchers said.
"The every-day man and woman need to exercise moderately to maintain health. However, our findings suggest that those at risk of weaker bones might want to take up running rather than swimming or cycling," said Giovanni Lombardi from Istituto Ortopedico Galeazzi.
One theory that could explain the effect of different exercises on bone formation is the role of osteocalcin, said Lombardi.
"Previous studies have shown that osteocalcin communicates with beta cells in the pancreas, which regulate the body's glucose metabolism," he said.
"Because running exerts a higher physical load on bone than swimming or cycling, it could be that these forces stimulate bone tissue to signal to the pancreas to help meet its energy needs in the long-term," he added.
