SCIENCE FRIDAY Boston WEEK 2017: IS RUNNING (TRAINING) GOOD FOR BONES?

Mackinac Bridge at sunset, looking north towards St. Ignace, Michigan. Taken by PKSenagore August 2016. All rights reserved.

IS RUNNING GOOD FOR BONES? THE BOSTON MARATHON IS!!! There may be other research that addresses the topic of bone strength and how to build it, but work  discussed below is the most helpful to runners that I've found.

The article, “Does Running Strengthen Bone?” by French scientists A Boudenot, Z. Achiou, and H Portier investigates the contribution of running to bone strength.  It begins by discussing general principles.  A strong skeleton, it informs readers, is one that “will be less prone to fractures”. Bone strength can be defined by qualitative and quantitative measures, including the determination of bone mineral density (BMD), which indicates the amount of calcium, phosphorus, and other minerals incorporated in bone. BMD is commonly used for this purpose, as it negatively correlates with fracture risk (a low BMD is associated with higher risk) in certain populations.

[There isn't total agreement that BMD is the best measure of bone strength, but is used clinically to asses fracture risk]. 
 
The paper describes in detail how bone becomes stronger physiologically. “Like a muscle, a skeleton needs exercise to be strengthened. It is estimated that only 30%–50% of potential bone mass can develop in absence of exercise… In fact, it is both mechanical stresses acting directly on bone (ground impact, pulling of muscle attachments) and biochemical agents transported by the blood (hormones, cytokines) that allow bone anabolism”, another word for construction.
 
Theoretically, the authors say, physical activity is recommended as a strategy to “augment” (increase) bone mass. Female practitioners of sports that are the most “athletic”, like “body building, judo, and rugby”, and gymnastics and tennis are more likely to have higher bone mineral density (BMD) than non-practitioners, they report.   This kind of information “suggests that sports requiring the movement of heavy loads or that expose skeleton to repeated impacts stimulate bone formation”.
 
“In contrast, endurance sports that primarily use the aerobic energy system (walking, running) result in smaller bone mass gain because the body is not subjected to high impacts.” YIKES!
 
This information is scary to me, because exercise prescribed for adults as we get older mostly involves aerobic training. Even combining aerobic work with resistance exercises doesn’t seem to greatly improve BMD or prevent BMD decrease, the authors indicate.
 
What’s the answer? The scientists say NOT to abandon aerobic training as it helps prevent cardiovascular, metabolic, and other diseases like hypertension, obesity, diabetes, and even some cancers. This advice should especially be applied in industrialized countries where people lead mostly sedentary lives. Best to “maintain these good habits with some ‘OSTEOGENIC’ modifications” to they advise, “by the integration of interval exercises and downhill running or walking”.
 
WOW. The same INTERVAL TRAINING that COACHES have been instructing runners to perform to build stronger muscles works to strengthen bones! It makes sense, because, as explained above, the mechanical pulling action of muscles at sites of attachment to bone plays a role in the strengthening process. Larger stronger muscles will exert a greater amount of pull on the bones to which they are attached.  

More good news is that interval training does triple duty when it comes to health.  The scientists say “it’s been observed that interval training has SUPERIOR effects” compared to “CONTINUOUS ENDURANCE TRAINING for the health of elderly suffering from cardiovascular diseases."
 
Why do these researchers recommend high intensity interval training, characterized by alternating work and recovery phases, over continuous running? Bone cells called osteocytes are initially stimulated when high intensity impact loads are sensed, but soon become fatigued, they say. Animals studies show that “5-10 minutes of running offer the same effects on bone as 1 hour of running”. “For a given exercise, adding a few seconds of recovery several times in the workout increases the positive effect on bone by 5-8 fold.” There aren’t any human studies of the same type, however.
 
DOWNHILL RUNNING was also prescribed to increase bone strength. How does it do this? Two ways. First, as stated in the second paragraph of this post, GROUND IMPACT is a MECHANICAL factor known to play a role in building bone. Downhill running increases ground reaction forces, and thus “offers an opportunity” to build bone strength with each step.  

Second, also stated in the second paragraph, BIOCHEMICAL factors are known to play a role in bone construction. Downhill running causes the release of a certain biochemical factor into blood that stimulates bone formation. Additionally, the eccentric contraction of muscle that characterizes downhill running causes a decrease in a biochemical inhibitor of muscle and bone formation (allowing increased formation of both to occur!).
 
The authors of this paper conclude by reminding readers “that bone is a living tissue that needs exercise to remain strong”.  Rather than abandon or interrupt existing habits of aerobic exercise, which provide benefits to cardiovascular and metabolic health, they recommend adapting running and walking such these activities become OSTEOGENIC (bone creating). This means “integrating rest intervals to prevent bone fatigue” and incorporating “downhill exercises to increase ground impact forces and eccentric muscular work”.
 
HOW DOES “BOSTON” BUILD BONE?  It is famously known to be a “downhill marathon”, with a net elevation drop of 477 feet. Of course there are other downhill marathons, and some wonder if the increased number offered is due to an increased desire by runners to  qualify for Boston. Preparing for a downhill marathon involves downhill training sessions. BOSTON STRONG!
 
RUN HAPPY!

http://www.nrcresearchpress.com/doi/abs/10.1139/apnm-2015-0265?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed&#.WO1U9hD4gnM

http://www.clevelandclinicmeded.com/online/casebased/ccjm/compression-fractures-normal-bone-density/media/CCJM-v76-6-331.pdf
 
http://strengthrunning.com/2011/04/running-downhill-boston-marathon/
 
http://www.findmymarathon.com/marathon-news/ten-options-for-downhill-marathons/