Are You Racing Towards a Fracture?

Cardiorespiratory fitness is a critical component of an athlete’s health and performance.  There are numerous physical and psychological benefits to aerobic training.  Just ask any endurance athlete how their training makes them feel and they would give a list of reasons everyone should train for aerobic capacity.  While the benefits of endurance training greatly outweigh the inherent risks, it is still important to understand the potentially negative side effects to prevent injury and promote long term health.

A recent article published in Current Sports Medicine Reports reviewed bone health in endurance athletes. It was noted that long distance athletes including swimmers, runners, and cyclists typically have lower bone mineral density (BMD) than athletes participating in power or ball sports.  The clinical application of low BMD places these types of athletes at a greater risk for stress fractures in the present and as the athlete ages.  So why does this happen to endurance athletes?

Wolfe’s Law predicts that bone will respond and form in direct relationship to the types of stress it is placed under. Using this principle, weight-bearing exercise has long been prescribed to increase BMD.  This would also explain why swimmers and cyclists have a lower BMD because their body weight is being supported by the water or bicycle seat, therefore taking the load off of the bones.  But what about long distance runners?  As it turns out, the repetitive nature of long distance running produces a low force output, generally in a single direction.  An efficient running economy reduces the impact from stride to stride, and most running shoes are designed to cushion each step.  In contrast, power sports and ball sports focus on generating maximal force output which involves sprinting, jumping, and changing directions.  This greatly increases the stress on the bones and contributes towards an increased BMD. 

Another contributing factor towards bone health in endurance athletes is energy availability, which can be defined as the total calories consumed minus the calories burned during exercise and divided by the fat free body mass.  This is the remaining energy to support normal body function.  Low energy availability can disrupt hormone cycles, which in turn can have detrimental and often irreversible effect to bone health.  This caloric deficit can be caused by not eating enough calories, excessive exercise, or a combination of both.  In female athletes, this imbalance can result in low levels of estrogen and makes them susceptible to functional hypothalamic amenorrhea (FHA).   Increasing dietary intake is enough to resume normal hormonal function without cutting back on exercise volume.

Here are some helpful tips to maintain bone health in endurance athletes:

-Eat a well-balanced diet that meets the demands of your training

-Make sure to consume enough calcium and vitamin D

-Reduce the amount of caffeine in your diet

-Perform weight bearing exercises like lifting to promote bone density, try for 2-3 full body workouts throughout the week

-Have a DEXA bone density scan performed to screen for osteopenia and osteoporosis

-Talk to your doctor if you think you might be at risk

 

References:

1. Scofield KL, Hecht S. Bone Health in Endurance Athletes: Runners, Cyclists, and Swimmers.  Current Sports Medicine Reports. 2012, 11:328-334

2. DeSouza MJ, Williams NI. Beyond Hypoestrogenism in Amenorrheic Athletes: Energy Deficiency As a Contributing Factor for Bone Loss. Current Sports Medicine Reports.  2005, 4:38-44