Does Biking Build Brittle Bones?

A recent study shows two-thirds of pro cyclists have weak bones. What's that mean for us amateur riders?

A wise man(guy) once said that there are two kinds of cyclists: those who have broken their collarbones and those who will soon break their collarbones.

Busted clavicles are painfully ubiquitous in la vie en vélo. They’re relatively thin bones and, when you hit the deck going 30mph+, they’re often among the first points of impact. There probably aren’t preventative measures that can 100% protect your shoulder in a tumble like that—except maybe not falling in the first place. That said, logic suggests that fragile things break easier than strong things. Therefore, bone health is something all cyclists should take seriously.

While the knowledge that cyclists often have brittle bones is old news, a new Dutch study suggests that as many as two-thirds of pro cyclists have low bone mineral density (BMD). That’s a lot of weak skeletons for such a tough subset of humanity!

In the study, 93 male and female early career, advanced career, and post-career elite cyclists were tested. Early career women and advanced career men and women were the worst off, but the issue persisted even for the retired pros.

Suspected reasons were “low BMI, fracture incidence, lack of bone-specific physical activity, and low energy availability.”

Today, we’ll take a look at this list with an eye on protecting dem bones. But first, let’s learn exactly what bones are.

Basic Boneology.

Skip this section if you’re not feeling geeky today.

Unlike hair and nails, bones are not dead. They’re living structures that constantly breakdown and rebuild themselves in a process known as remodeling, bone turnover, or bone metabolism. This allows bones to heal after injury and to respond to stress. Injury aside, the overall process takes about ten years. In other words, we basically get an entirely new skeleton every decade.

Bone has several layers. The hard, outer layer is called cortical bone. Next is a spongy layer of cancellous (or trabecular) bone. Inside that, there’s a canal where you’ll find the marrow, a tissue that produces various cells including white and red blood cells.

Both cortical and cancellous bone are made of a number of different types of cells, but they primarily consist of two things. One is collagen, which provides a framework. The other is a form of calcium phosphate called hydroxyapatite, which adds strength and hardness.

You don’t need to know most of this to benefit from the next section, but I thought it was interesting, so I brought it to Show and Tell.

The issues the Dutch study blamed for weak bones—and some potential solutions.

Low BMI: Low body mass index is a fancy way of saying you’re probably too skinny. It’s super well-documented that low BMI is a risk factor in fractures—and serious cyclists are often beanpoles.

That said, according to this meta-analysis, BMD is a more important factor than BMI. In other words, bone-supportive nutrition and exercise go a long way towards helping you avoid fractures, even if you’re really thin.

Fracture incidence: Research suggests that when you break a bone, it can lead to weakening across your entire skeletal system. Experts aren’t completely sure why, but it appears to be related to inflammation.

I can’t really give you any tips on this one except to say, “Try not to break your bones.”

Lack of bone-specific physical activity: Bones work a little like muscles. When you stress them, you strengthen them. Bike riding has very little impact on your skeleton, therefore it doesn’t cause your bones to remodel stronger.

On the other hand, weight-bearing exercise is “osteogenic,” meaning it causes bones to build back denser as they remodel. Running has also been shown to be osteogenic.

As a bonus, strength training has been shown to improve your cycling economy (how efficiently you use fuel when you ride) and VO2 max. It may also improve sprint speed. (That last link shows a connection between strength training and sprinting for runners, but I think including cycling is a fair extrapolation.)

Low energy availability: You probably thought this section was going to be about the need for calcium. Or vitamin D, which helps absorb calcium. Or magnesium, which helps absorb vitamin D. Or vitamin K2, which helps calcium move through your system. Or maybe even protein, which is the stuff collagen (your bone “framework”) is made out of.

Yeah, you need all these things, but more importantly, you just need food. As we discussed a few weeks back, it’s pretty tempting for athletes to go on low calorie diets to lose weight. Sadly, when you drop your energy intake too low, even for a short period of time, it impacts your hormones which, in turn, impacts your body’s ability to form new bone.

There may be a few hormones at play here, but I’m referring specifically to leptin, a hormone tied to both energy and bone metabolism. Leptin inhibits hunger, so when you starve yourself, your leptin levels decrease as to increase hunger. It’s your body’s way of coaxing you into eating. However, hormones often multitask. Leptin also regulates bone metabolism. When it decreases, your bones don’t remodel properly—so you lose weight but you also lose bone mass.

When you put it all together…

Amateur competitive cyclists can plunge head first into some pretty risky behavior. They under-eat, they over-train, and they obsessively ride their bikes—all in the name of progress (and fun).

Frankly, it’s unlikely that going overboard like this will make you any faster, even if it makes you feel pro. Considering that studies like this indicate that the majority of pros are setting themselves up for osteoporosis, maybe ask yourself if it’s worth it.