Alex Hutchinson draws on the latest research to answer your fitness and workout questions in this biweekly column on the science of sport.
What type of exercise is best for maintaining strong bones?
The key word here is "maintain," as 95 per cent of your mature skeleton is already in place by the age of 17 for girls and 19 for boys. Once you reach adulthood, it's basically one long fight against the slow but inexorable loss of bone strength - and the key to that fight, many of us assume, is weight-bearing activities.
But the latest research shows that resistance-training exercises like lifting weights can also play a crucial role in bone health - and in some cases are even more effective than weight-bearing activities such as elliptical training.
"Over the past decade, people have realized that bone is more dynamic than we thought. It's actually a pretty responsive tissue," says Heather McKay, a professor in the faculty of medicine at the University of British Columbia and the director of the UBC/Vancouver Coastal Health Research Institute's Centre for Hip Health and Mobility.
As a result, training your bones has a lot in common with training your muscles: The results of a given exercise will depend on what your body is currently used to, how big a load you apply and how you apply it. For example, recent studies by Dr. McKay's team have found that short bursts of intense activity with rest periods - anything from jumping on the spot to squats in the weight room - build bone more effectively than continuous activities.
While the skeleton gets a bit of a workout whenever you're standing up, you can stress your bones in a more targeted manner by training with weights.
"Any time you're increasing your muscle mass, the tension of the muscles on the bone creates a 'bending moment' that stimulates your bones," Dr. McKay explains.
In fact, numerous studies over the years have suggested that resistance-trained athletes have greater bone mineral density than endurance-trained athletes. But an article that appeared in the February issue of the Journal of Strength and Conditioning Research suggests that these conclusions need to be rethought.
Pamela Hinton and her colleagues at the University of Missouri compared runners, cyclists and resistance-trained men. While the resistance group did have the greatest bone density, the differences were only relative: The runners were leaner, but their bones were just as strong for their body size.
There was, however, a sign-ificant difference between runners and cyclists: The repeated, jarring impact of running resulted in stronger bones than cycling. As a result, Dr. Hinton recommends that those who engage in activities such as cycling, swimming and rowing consider adding a dose of either resistance training or a higher-impact activity such as running to their regimen.
That means that elliptical trainers, which many people turn to precisely for their softer landing, suffer from the same shortcoming, Dr. Hinton notes. "There is no impact force, as the steps of the machine move with you."
Sports such as soccer and basketball (and activities such as step aerobics) offer the best of both worlds, stimulating bone health through the impact of intermittent jumping and running, as well as by building muscle strength. Dr. Hinton's research suggests that you don't necessarily have to lift weights, and you don't necessarily have to run or jump either - but you should be doing at least one of the two.
Alex Hutchinson blogs about research on exercise and athletic performance at http://www.SweatScience.com.
Bone density for kids
A quarter of your adult skeleton is laid down during early puberty, making it a crucial time to build bone strength. A University of British Columbia study found that jumping up and down between five and 15 times, three times a day (at the morning, noon and end-of-school bells) significantly increased bone density in B.C. schoolchildren.