Wednesday, July 08, 2009

Is Cycling Bad for Your Bones?

Some recent studies indicated that too much cycling might cause bone loss (see NY Times synopsis below). Since we spend more time on the bike, as triathletes, than any other sport, I found this very alarming. Could this be true? In one study, competitive cyclists had less bone density than controls (men who were active but not competitive). Some even had osteopenia, the early stages of osteoporosis. These men were in their late 20s, not 70s! The 2nd study found that a different group of competitive cyclists lost a significant amount of bone throughout the race season (although, luckily, they regained some of it in the off season). A third study compared bone density between weight lifters, runners, and cyclists. Guess which group had the lowest? Yup. The cyclists. However, in another study, triathletes gained bone density throughout the race season. Huh? (But, yea!)

Why would cycling cause bone loss? Some have postulated it's due to the non-impact nature of the sport. Perhaps. It is known that weight lifting and running increase bone density. But that doesn't explain the net loss of bone. I think these studies have to be taken with a pound of salt because they were all done on competitive cyclists, a group of athletes known for not making the healthiest choices for their bodies (doping, anyone?). The amount of stress they put on their bodies in a season is extraordinary. In addition, extreme weight loss is known to cause bone loss (leading to osteopenia and osteoporosis) in people with eating disorders, especially anorexia. Competitive cyclists are notorious for starving themselves into an unhealthy "race weight", believing it will lead to faster performances (which is wrong--it depletes the immune system and causes fatigue, actually slowing you down). I would hypothesize that the competitive cyclists used in these studies suffered from bone loss due to their low weights and not the cycling itself. It would be interesting to repeat these studies in non-competitive cyclists.

That said, the study that looked at triathletes reported an increase in bone density over the season. Could it be that triathletes participate in more impact sports (e.g. running)? They have higher percentages of lean muscle mass? Or were they at a healthier weight?

Some food for thought....literally


Kate said...

Very interesting. Without knowing more, I certainly find your hypoethesis pretty compelling!

Kevin said...

Interesting. Maybe there bones are giving up their calcium due to diets severely lacking in calcium.

Diana said...

That would suck if true, biking is my favorite of to my kettlebell training that is!
Thanks for the link!

bunnygirl said...

I read a few years ago that calcium loss through sweating, combined with the low-impact nature of the sport was the main reason they thought this was happening.

Also, most competitive cyclists are small and/or light-boned to begin with, since the sport favors that body style. They're coming from a place of having less they can afford to lose and they do little, if anything, to counteract potential bone loss.

Most of the rest of us run, lift weights, or do some type of load-bearing activity in addition to cycling. Just to be on the safe side, though, it's a good idea to take a calcium-magnesium tablet after a particularly long sweaty workout, and supplement with D3 if one isn't getting any sun.

Wes said...

Yea, I was gonna say I wouldn't worry about us too much. We run too... but I can see how competitive cyclist might get that way. Surely they lift though, and would lifting not promote healthy bones? I guess if their diet is bad, then no...

Grey Beard said...

I average 8-10 hours a week in a 1G environment, the other ~160 hrs I am doing what everyone else is doing, so can't think distributing my weight across pedals, saddle, handlebars is the problem. When lying in bed sleeping people don't seem to lose bone mass, so it can't be the lack of bearing weight that is the problem.

Mountain climbers have reported for years that when breathing hard one loses a lot of CO2, so maybe that is a factor.

When you have riders like that French freak that weights ~ 140 and is 6'1" who won stage 7 I think anorexia is a big factor.

I find the report unsettling, but wonder why, historically, tour riders have not had the medical problems attendant with osteoporosis?

A good place to start looking for the root cause would be in a postmortem skeletal exams of past champions, before the age of performance-enhancing drugs. Anyone have a spare shovel?

Grey Beard said...

A final thought, if bearing weight was the dominant factor, then those in professions like hod-carrier should have extra dense bones. Is this true?