Young elite cyclists with surprisingly weak bones

Road cyclists have incredibly strong muscles in their thighs and shins. However, the news about their bones is not quite so good.

Several crashed bicycles and people
Falling off in the cycle lane and subsequent fractures are not uncommon. Illustration photo: Shutterstock
Portrait of Oddbjørn Klomsten Andersen
Oddbjørn Klomsten Andersen Photo: Private

Weakening despite hard exercise

Generally speaking athletes have higher bone mineral density than people who are inactive because they do more weight-bearing exercises which impact on the skeleton. However, athletes engaged in non-weight-bearing activities, such as swimming and cycling, are more likely to suffer from weaker bones.

A study conducted by Andersen, et. al. entitled "Bone Health in Elite Norwegian Endurance Cyclists and Runners: A cross-sectional Study" - monitored bone-mineral density in 19 elite road cyclists and 21 elite runners in Norway. These included men and women between the ages of 18 and 35.

The BMD of the cyclists was lower than that of the runners. Ten of the 19 cyclists were classified as having low bone mineral density. This means that according to the criteria set by the American College of Sports Medicine (ACSM) they were one Standard Deviation below the average.

Measuring BMD

The strength of bone tissue can be measured by undertaking bone density measurement tests. This is done using a DXA machine which scans the skeleton and produces images. The WHO defines osteoporosis on the basis of DXA measurements.

CT scanning which produces 3D images can also be used. These enable one to say more about the micro-structures and thus the strength of the skeleton.

Bone mass

Maximum bone mass is developed by the age of 25, after which it is gradually reduced with age. Lost bone mass is difficult to regain, so it is important that we protect ourselves against this.

In women the loss of bone mass increases rapidly after the menopause due to falling oestrogen levels. Oestrogen is a hormone which protects the skeleton from losing calcium, and a drop in oestrogen levels can thus result in a loss of bone mass.

The skeleton is largely composed of calcium, and calcium intake is therefore extremely important - in addition to bodybuilding exercises and general training. (

The skeleton is largely composed of calcium, and dietary calcium is therefore extremely important - in addition to bodybuilding exercises and general training. (


In osteoporosis the structure of the bones is changed as a result of low calcium levels. This makes the bones more brittle and increases the risk of sustaining fractures, often in the vertebrae, the femoral neck or the lower arms.

Osteoporosis is more common in women than men, and occurs more often with increasing age. (

Importance of bodybuilding exercises

The best exercises for strengthening the bones are weight-bearing or bodybuilding exercises. Research has shown that heavy bodybuilding exercises in particular are an effective way of preventing the loss of bone mass. The advantage of bodybuilding is that it exerts pressure on the skeleton at common fracture points such as the hips, lower arms and lower part of the spinal column.

Not enough weight training?

—Was this particularly surprising?

—The surprising thing was that these 10 cyclists had low bone mineral density despite doing heavy weight training for a minimum of two months per year, says Oddbjørn K. Andersen. According to the ACSM criteria, one of the cyclists had developed osteoporosis.

—So what can these low rates be attributed to?

—I think that a lack of weight-bearing exercise could be one of the explanations. Many of the cyclists have probably only done heavy bodybuilding exercises outside the season. It’s possible that this is not enough to produce any effects on the skeleton, says Andersen. —At the same time we mustn’t forget that this is a cross-sectional study and that the bone health of these cyclists might have been even worse if they had not done any bodybuilding exercises. But unfortunately we don’t know that for certain.

Calcium loss through sweating

In cycle sports and, for that matter, long-distance running, it is an obvious advantage to have a low body weight. Cyclists talk about the “power-to-weight ratio”. A higher ratio is often synonymous with better performance. It is often easier to lose weight than to increase strength (watt strength). Doing a lot of exercise without having much energy available in an attempt to lose weight can result in hormone imbalances which have an adverse impact on bone health.

Vital functions keep the calcium balance in the blood within narrow margins. During long-term training in a hot climate the body loses a lot of calcium through sweating. This calcium needs to be replaced. If the body does not obtain enough calcium from food and liquids it will take it from the skeleton. This could potentially result in more brittle bones over time.

—What are the consequences of low BMD values for young cyclists?

—A porous skeleton is more liable to sustain fractures during falls, and as we know, falls are relatively common in road cycling. Thus the utmost consequence of this is that low bone mineral density can result in more and longer time out for injuries among young cyclists. After the age of 30 it is difficult to increase one’s BMD values, so what will happen to the long-term bone health of these athletes is not certain, says Oddbjørn Klomsten Andersen.

Variation is important

Oddbjørn Klomsten Andersen has clear recommendations about how to develop strong bones, particularly during the growth phase which occurs prior to the age of 25. The same applies to preventing the loss of too much bone mass later on in life.

  • Always exercise
  • Do bodybuilding exercises
  • Activities involving jumping and frequent changes of direction strengthen the bones (e.g. ball games and tennis)

How a Master’s thesis ended up in the NY Times and The Times

Oddbjørn wrote his Master’s thesis at NIH (the Norwegian School of Sport Sciences) in 2017. An article written by him and his colleagues at the Department of Sports Medicine was published in BMJ Open Sport and Exercise Medicine in November 2018 and was subsequently picked up by both the New York Times and The Times.

—Why do you think that your article received so much attention?

—I hope that it is because this is an exciting, important subject, especially for young athletes. One of the questions that the NY Times and The Times asked was whether or not the results could be generalised and whether or not our findings could be transferred to ordinary people who use a bike either for excise or as a means of transport, he says.

—If that had been the case, it would have affected a lot of people. But the results cannot be generalised to apply to the population at large because this tendency occurs when unilateral, hard cycling is combined with low body weight.

Read more about other projects undertaken by NIH Master’s students (in Norwegian)

Some study weaknesses

—One downside is that this is a relatively small study. We decided to recruit high-level athletes at the expense of the size of the selection. This meant that we probably missed some of the associations between independent variables and BMD, says Oddbjørn K. Andersen.

He believes that we also need similar studies which could be conducted over a longer period of time.

—It would be very useful if we could monitor BMD in young cyclists and look for any changes during the season. This might provide us with a better understanding of any variables which might impact on bone mineral density.

Bodybuilding and eating enough food are important

In his capacity as a former Continental Team cyclist, Oddbjørn Klomsten Andersen has observed a number of cyclists who train a lot and only do cycling, possibly without having an adequate food intake. Based on his background he wanted to undertake a more systematic study of bone health in elite cyclists and runners for his Master’s thesis.

Trine Stensrud, who was Oddbjørn’s main supervisor for his Master’s thesis and one of the co-authors of the article, thinks that the study has been important for identifying bone health in elite cyclists. The next stage would be to undertake a randomised, controlled study in order to see if systematic bodybuilding exercises could result in better bone health in young cyclists.

Professor Stensrud emphasises that weight-bearing exercise and bodybuilding, as well as having an adequate intake of energy, are important for good bone health in athletes and people engaging in exercise in all age groups.

—The study shows that it is particularly important for cyclists to engage in weight-bearing exercise and that they need to obtain enough nourishment and calcium in order to develop a strong skeleton.

—Most people know that they should engage in regular bodybuilding exercises in order to strengthen and maintain their muscle mass. The fact that bodybuilding is also important for bone density is an important message to get across, points out Trine Stensrud.