Osteoblasting

My friend, Patsy, is a cyclist and has been since she was in high school.  One night over dinner in Montana, we were talking about the Tour de France and the workout that the cyclists get when they are competing.  Patsy mentioned that the bone density of professional cyclists is continually measured because cyclists can lose bone mass over the course of a season.  She noted that swimmers have the same issue.  I was surprised to hear this and decided that I needed to do some research to learn more.

I started with an Internet search and found many articles and studies about swimmers, cyclists, and even kayakers having lower bone mineral density (BMD).  BMD indicates risk for bone fractures by measuring how much mineral (e.g., calcium) you have in your bones.  There are several ways to measure BMD.  A DEXA (dual energy x-ray absorptiometry) scan is the most common and measures specific areas of the body – spine, hips, and forearm.   The scan results will indicate if your bones have sub-normal bone density (osteopenia) or if you have deterioration of the bone tissue (osteoporosis).   Studies have been done of cyclists and swimmers where their BMDs were compared before and after their competitive seasons.  In the studies I read, there was a decrease in BMDs in both cyclists and swimmers between those two points in time.

I know many people who are dedicated cyclists or Master’s swimmers.  It was hard to think that by being so intensely active in their sport of choice, they could actually be hurting themselves.  Physical activity is suppose to keep you healthy.  But the scientific evidence clearly shows that too much time in the water or on the bicycle seat can be harmful.

My husband can’t run due to an issue with his knee.  He likes to ride a bike and has even completed a Century Ride (100 miles).   His first question when we started talking about this was “why is cycling bad for my bones?”

This week while Jessica, my physical therapist, worked on my arm, I asked her to explain why cycling and swimming would lead to lower BMD.  Jessica put it in very basic terms for me.  She explained that there are three primary types of bone cells – osteoblasts, osteoclasts, and osteocytes.  In order to build up bones, our bodies need osteoblasts.  Osteoblasts are bone cells that create  the framework for new bones (or bone remodeling as she put it).  Stress on the skeleton from weight-bearing exercise increases the workload on the bones and triggers osteoblastic activity or the remodeling process.  Osteocytes are mature bone cells that originate from osteoblasts.  Osteoclasts are cells that break down the bone.  Reduced workload on the skeleton from things like prolonged bed rest and some medications will increase the osteoclastic activity and lower bone density.  And yes, prolonged sitting is bad for bone health.

Swimming is a great exercise to build and maintain muscles and improve flexibility and balance.  Jessica says that she recommends swimming for her patients that have arthritis and have to avoid high impact activities.  But swimming doesn’t put stress on the skeleton because of the buoyancy of the water.  It is almost like an anti-gravity exercise.  Therefore, swimming doesn’t trigger osteoblastic activity.  (As a side note, astronauts in space lose BMD, indicating that we need the stress of gravity on our bodies.)

Cyclists are sitting on a seat when riding and likewise cycling doesn’t trigger osteoblastic activity (though standing up on the pedals may make it a modest weight-bearing exercise).  The same is true for kayakers who are seated when they are paddling.  No weight-bearing exercise there.  Elliptical trainers are popular in the gym but according to the Mayo Clinic, they are not helpful for improving bone health.  Ellipticals provide great cardiovascular exercise but not weight-bearing exercise.  According to the American Academy of Orthopedic Surgeons, weight-bearing exercise is any activity you have to do on your feet like running, walking, climbing stairs, racquet sports like tennis, and strength training.

So what is a swimmer or cyclist to do?

Building bones during the 2015 Tokyo Marathon

Building bones during the 2015 Tokyo Marathon

We need to have a variety of exercise activities.  Replace some of those swimming or cycling days with running or strength training exercises.    I am a runner but my coach mixes up my training activities.  I only run three times a week.  The other days I ride a recumbent exercise bike or do strength training exercises.   And I try to squeeze in a daily stretching routine.  I have always believed that too much of anything is bad.  This is true with exercise.  We need to have a balance of exercises – cardiovascular, weight-bearing, strength training, stretching and flexibility.

This weekend I will be out on the trail for my long run, “osteoblasting” my way through 18 miles.  I will be thinking about all those strong leg bones I will be building up as I run.