Cycling and bone health: what all cyclists need to know to stay strong

Andrew Hamilton looks at new research comparing bone health in runners and cyclists, and makes recommendations for cyclists seeking to maximise bone mineral density

Without doubt, cycling is one of the very best exercises for promoting long-term health. Numerous studies have demonstrated that compared to their sedentary peers, cyclists who undertake rigorous training can expect to enjoy a number of health benefits. These include:

1. Enhanced insulin sensitivity⁽¹⁾;
2. Reduced blood pressure^(2,3);
3. Improved blood cholesterol profile^(2,3);
4. Reduced body fat⁽⁴⁾;
5. Reduced risk of coronary heart disease (as the result of 1-4)^(5,6);
6. Better quality of life in older age⁽⁷⁾;

Even better, its low-impact nature means that cycling is a sport that can be enjoyed by athletes from all backgrounds, including those who might be otherwise prone to overuse injuries or those seeking to stay fit well into old age.

Importance of bone density

However, one area where cycling might not deliver health benefits is bone health, or more specifically, increasing bone mineral density (BMD). Developing high levels of BMD is important because low levels of BMD are associated with an increased risk of osteoporosis. Translated literally, osteoporosis means ‘porous bones’, and is defined by the World Health Organisation (WHO) as ‘a progressive systemic skeletal disease characterised by low bone mineral density (BMD) and micro-architectural deterioration of bone tissue, with consequent increase in bone fragility and susceptibility of fracture’.

In simple terms, this means that as bone mass is lost, the mineral structure of the bone becomes progressively more porous, with microscopic gaps appearing in the structure that both weaken the bones and make them more brittle and less able to withstand knocks and shocks without damage. In short, bones that were once strong can break very easily. In severe cases for example, a simple stumble can result in a broken leg or hip. All bones can be affected by osteoporosis but fractures are most common in the wrist, spine and hip.

Once we reach the age of 40, some degree of bone mass loss due to the aging process is inevitable (see figure 1). However, osteoporosis is a far more extreme condition, which is linked to a number of lifestyle factors including exercise habits and diet. Scientists now believe that large volumes of endurance training can increase the risk of osteoporosis.

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Figure 1: Bone mass changes and age*

^# *Graphic courtesy of Dr Felicity Kaplan

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Being physically inactive is a major risk factor for developing osteoporosis. This is because vigorous ‘bone-loading’ physical activity is very effective at stimulating the uptake of calcium into bones, thereby helping to build bone mass in earlier years, and reducing the loss of bone mass in later years⁽⁸⁾. But what about physical activity with minimal bone loading?

The best bone-loading sports

Research has shown that the higher the muscular and impact load (gravitational) forces, the higher the BMD produced; so for example, gymnasts whose sport requires high loadings and impacts tend to have higher BMDs than endurance runners⁽⁹⁾. There’s also evidence that activities that develop strength (such as weight training) are particularly effective at producing high BMDs in the hip and spine^(11,12). By contrast, those who participate in sports with plenty of muscular motion, but without substantial loading (eg swimming) do not achieve the high BMDs of sports with higher loading⁽¹⁰⁾.

Cycling and bone loading

The smooth spinning nature of the pedalling action and the fact that cyclists are supported by their saddle means there’s virtually no bone loading associated with gravitational impact (unlike the shock of foot-strike during running or field sports). When road cycling is an athlete’s main or only sport, the degree of total bone loading is likely to be quite low. These factors have prompted a number of studies looking at BMD in cyclists, and the findings have been worrying.

For example, French scientists found that compared to healthy non-cycling males, road cyclists had lower levels of BMD, and this was despite the fact that they were consuming significantly more dietary calcium (considered essential for bone health) than their sedentary counterparts⁽¹³⁾. Another study by an international team looked at 30 pro cyclists who had participated in at least one of the main 3-week stage races (Giro d ’ Italia, Tour de France or Vuelta a Espana) in each of the previous three years⁽¹⁴⁾. It found that the pro cyclists had significantly lower levels (9.1% less) of BMD than sedentary controls. Even more alarming was that in the lumbar vertebra of the lower back and femoral neck (ball joint at the top of femur), BMDs were 16% and 18% lower respectively. Over the years, other studies have concluded that athletes participating in high volumes of non bone-loading exercise such as cycling and swimming are at risk of low BMD⁽¹⁵⁾.

Running and weights for cycling bone health?

In the pro cycling study above⁽¹⁴⁾, the researchers reasoned that the poor BMD results were likely due to the fact that none of the cyclists had engaged in other forms of (better) loading exercise such as running or weight training. It’s for this reason that health professionals now advise cyclists to add these kinds of loading exercise to a cycling programme. But is this true? Can cyclists really protect their bone health by pounding the streets or hitting the gym?

This is a question that Norwegian scientists have looked at in great detail in a newly published study⁽¹⁶⁾. They noted that (as mentioned above) research has demonstrated high prevalence of low BMD in competitive cyclists. However, they also noted that low BMD has been observed in elite middle-distance and long-distance runners, despite these athletes competing in a weight-bearing sport^(17,18). One common factor that both distance runners and cyclists share is low body mass and ‘low energy availability’ (ie where the total calorie intake is only just sufficient to support training and essential metabolic processes in the body), both of which have been linked to low BMD in several studies^(19,20).

To try and obtain a definitive answer, the researchers evaluated and compared the bone health of 21 long and middle-distance runners (11 females and 10 males) and 19 road cyclists (7 females and 12 males). All the athletes were training and competing at an elite level. Interestingly, 16 of the cyclists reported performing lower-body heavy resistance training in the previous two years, and 15 of these had participated in heavy resistance training during the season in which BMD was assessed. By contrast, only five of the runners reported engaging in heavy resistance training.

The uncomfortable results

Using a (highly accurate) scanning technique known as DXA, the researchers compared total body, lumbar spine and femoral neck BMD in the cyclists and runners. What they found was as follows:

• The cyclists had lower BMD for all measured sites compared with the runners.
• Ten of the 19 cyclists were classified as having low BMD. This was DESPITE their participation in heavy resistance training on the lower body.
• Low BMD was not confined to females, and was site specific, being particularly noticeable in the lumbar spine and the femoral neck.
• The type of sport was the only factor significantly associated with low BMD (ie factors such as diet, height, family history etc had no bearing).

In conclusion, these results suggest that the cyclists had lower levels of BMD overall than the runners. This was the case even when the cyclists were engaging in heavy weight training, which has previously been suggested as a way of offsetting bone mass loss.

This is a significant finding, as it’s the first study to show that adding heavy resistance training into a resistance training programme does NOT seem to prevent bone mineral loss in cyclists (and by implication in other low-impact athletes such as swimmers) undergoing high training volumes. Some caution is required as the data on the exact frequency and volume of the weight training was not comprehensive. However, the researchers argued that the most likely explanation for these worrying results was threefold:

• The high volumes of riding (which averaged nearly three hours per day) overrode any bone stimulating effects of the heavy weight training.
• Most of the cyclists were not resistance training through the whole year, and some only resistance trained in the off season (ie maybe all-year round resistance training is needed).
• Many of the cyclists had low body mass. While this may be desirable to enhance power-to-weight ratio, it can often only be achieved at the expense of having a ‘relative energy deficiency’ (ie insufficient energy/calorie intake), with implications for possible nutrient insufficiencies arising too.

Advice for cyclists

This article is not intended to alarm but to inform. If you are a concerned cyclist, you should also remember that this study looked at elite cyclists training 2-3 hours per day, every day. They were also very lean. If your training volume is lower, your diet is good and you’re not too lean, you probably have less to worry about! However, cyclists engaging in more serious training volumes should be aware of the potential risks that high-volume training poses to bone health – even if they combine some weight-bearing activity such as running and/or weight training into their training plan. The implications that follow for those wishing to maintain good bone health include:

• Weight-bearing activities should be incorporated into a cycling programme all year round – not just in the off season.
• Calorie/dietary restriction to lose weight/improve power-to-weight ratio is not advisable.
• Cyclists should ensure adequate energy availability at all times (see this article for more information and advice).
• Cyclists should pay particular attention to their calcium and vitamin D intakes (see this article for detailed advice on calcium and this article for optimising vitamin D intake).
• Concerned cyclists may wish to undergo a DXA scan (a very simple and non-invasive process) to get a current assessment of their BMD. This information can direct future training and nutrition strategies.

References

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