Ideasroom

Tackling a problem that grows with age

We have an ageing population here in New Zealand and, you would assume, we are all hoping to live actively, happily and healthily into a long old age. But unfortunately, for many of us, the passing years bring failing joints.

It is a really big problem: We are expecting a 700 percent increase in joint replacements in the next 15 years. This is unsustainable. And people are not only getting older, they are getting heavier and the two together are leading to an epidemic of osteoarthritis. 

So what can we do? Well, first off, prevention of joint and bone disease has to be made a healthcare priority; and secondly, we need to extend awareness of what we can do to improve our own bone and joint health and that of our children.

We already know that musculoskeletal tissues responds rapidly to a lack of activity. For example, astronauts who go up into space can experience up to 30 percent bone loss even though they might only be there for a couple of months. The fact is their bones aren’t ‘loaded’ enough (the muscle and reaction forces in the joints are reduced in non-weight-bearing conditions) and therefore the body self-regulates by reabsorbing bone tissue rather than maintaining bone mass. The old adage ‘use it or lose it’ applies to bone as well as muscle, cartilage, and other tissues.

So if you want to stress or excite your bones, the best thing you can do is apply large and rapid loads, like jumping off a table. Do that 10 times, and your bones will receive more stimulus than if you went for a walk for 10 minutes.

Stressing your bones during growth and development is incredibly important, because mechanical forces can regulate the size and shape of our bones and joints, beyond that pre-determined by our DNA. If we subject our bones to mechanical stress while we’re still young enough to be building them, we will make them strong. And bone strength has positive implications throughout our life in terms of our risk of bone diseases such as osteoarthritis and osteoporosis.

The direct link between biomechanical loading and bone health is clearly demonstrated in a study of baseball pitchers at various decades in their life by Indiana University. Researchers compared the bone shape and density of the throwing arm with the non-throwing arm. They had the perfect control, or comparison, for this study – throwing with one arm and not throwing with the other. This meant they didn’t have to consider biological factors or diet and that any changes or differences could only be linked to mechanical load.

For a baseball pitcher, the load comes from the cocking phase of the throw where the arm goes back into a torsional, or twisting load along its length. As a result, the pitchers throwing arm was thicker as a result of the bone getting larger in diameter in response to the load, as well as being twisted by about 20 degrees. And what is really intriguing is that bones maintained their strength even 30 or 40 years after they stopped playing sport – the modelling that occurred in the bone during their playing years remained - which confirms that the shape of the bone developed in our early life is maintained throughout our adult life.

This means what you do during growth and in adolescence really matters. It is the time when bones are growing and changing their size and shape, a process known as bone modelling. Loading young bones with stress at this stage increases their size and makes them strong. 

Ask kids in the classroom to get up and do ten star jumps every 20 minutes. This simple act will help to stimulate their bone growth and potentially reduce the risk of bone disease in 40 years’ time.

So is it too late to improve bone health after adolescence? Well, if you’re 30 and have spent your life sitting behind your computer playing video games and you want to start running marathons, it may not be a good idea because your joints and bones are not designed to withstand those loads. You would have to slowly build up to that level of exercise.

However, exercise is always good and while earlier in life is best for building a healthy skeletal system, there is a lifelong process called bone remodelling which renews our bone tissue when required. And like bone modelling, bone remodelling is also influenced by activities that put a strain on your bones. Brisk walking, or jogging, for example, places enough strain on the bone that the bone density can be maintained.

It’s worth noting that while two model activities for general health are cycling and swimming, but if this is all you do, you might be at risk of osteoporosis because there is much less load experienced by the bone in those activities. Even elite cyclists are at risk of poor bone health – they might be producing lots of power and energy in their muscles but they don’t have enough impact load in their bones 

So the message is clear – make sure our children and young people are involved in activities that will ‘stress’ their bones; find an impact activity that can help bone health in later life and remember – it’s never too late to jump off that table!

Thor Besier will be talking about bones and exercise tonight in Episode 10 of The Check Up,  the 10-part factual series in which experts clear up health myths and translate the best available evidence in fun, engaging ways. The Check Up, TVNZ 1, 9 Sept, 8pm.

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