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Thursday, September 1, 2011

Balancing the risks and benefits of endurance exercise

The health benefits of exercise are well-established.  A recent study published in the Journal of the American College of Cardiology showed that one’s fitness level, as measured a person’s one mile run speed, compared to other cardiovascular risk factors, was the best single predictor of heart attack risk and life span. Studies have shown that regular exercise reduces one’s risk of obesity, diabetes, and hypertension.  Exercise has been shown to benefit mood and alleviate the symptoms of depression.   On a cellular level, telomere length, a marker of mitochondrial health, has been shown to be improved in those who exercise.  Consequently, getting people to exercise more has been adopted as a top strategy of health promotion. 

I am an exercise zealot.  Growing up I swam and dove competitively.  As an 18 year old, fearful of the freshman fifteen, I took on running, and have been hooked ever since.   In my middle age, wanting to cross train more because of increasingly achy joints and muscles, I have ventured into bicycling.  We talk much of the health benefits of these sports, but what of the risks?  While exercise long term may be good, do the risks of injury and accident offset the potential for long term benefit and actually increase health care utilization?  Consider three of the most commonly practiced forms of exercise:  running, swimming and cycling.
As a sport, running carries the risk of overuse syndromes: runner’s knee (patella femoral syndrome), iliotibial band syndrome, plantar fasciitis, stress fractures, piriformis syndrome, and Achilles tendinitis, to name a few. Female runners may suffer from the Female Athlete Triad—amenorrhea, bone loss and disordered eating.   Marathon running is known to be associated with low bone density and may also increase oxidative stress.  Whether or not running is the cause of osteoarthritis of the knee is somewhat controversial.  MRI demonstrates knee abnormalities in marathon runners that are not seen non-runners.  Clearly in those already affected by arthritis or prior injury, running makes the condition worse.  Approximately 1 in 3 runners are injured per year of running.  

On the other hand swimming, as a sport, is relatively safe, unless of course you drown.  It turns out that 36% of swimmers who drown in Georgia are intoxicated while swimming—alcohol and swimming don’t mix. Otherwise, shoulder bursitis and rotator tendinitis are the most common swimming related injuries.

In my view, of the three sports, biking may be most risky. Approximately one in three bikers has an accident per three years of biking.  The annual rate of accident for regular bikers is about one and ten (less than running). However, in comparison with the debilitating overuse injuries of running, biking carries a more profound risk of serious injury and death.  Studies show that the risk of head injury and upper facial fractures may be reduced by 60 to 70% with helmet use.  Legislation requiring bike helmet use has increased compliance with this health-promoting behavior.   There’s also the threat of pudendal nerve injury and for men, erectile dysfunction.  A recent study showed 94% of asymptomatic male, mountain bikers had evidence of scrotal abnormality on ultrasound, presumed the result of chronic repeated microtrauma, compared to 16% of non-bikers who had abnormalities.  Avid bikers will tell you that proper seat ergonomics and padded shorts help reduced these risks of saddle injury.

In a triathalon a couple of years ago I took a hair pin turn too quickly, driving off the road into a grassy embankment.  Fortunately, I sustained only minor abrasions and was able to keep riding.  Others are faced with more serious injury.  Recently, in a tragic accident, a male physician biking across a bridge in Charleston, South Carolina was killed by a passing truck that hit him throwing him off the bridge. Bikes are no match for cars, and it's a drivers world that we live in unfortunately.
I exercise because I like getting outdoors and being active.  It gives me a sense of well-being, improves my mood, makes me more confident about my physique, and seems to keep my weight in check.  I hope it will result in further health benefits down the road.  The positive data seems good, however when prescribing exercise to promote health it’s important to weigh the balance of risk and benefit.   Despite popular notions, the practices of stretching and cross-training have not been convincingly demonstrated to reduce injury. Given the physical diversity of those who exercise and the lack of good data on what helps prevent injury, a common sense approach seems reasonable. Of course, as I write this blog with my calf resting on a bag of ice, talking common sense to an exercise enthusiast can be a challenge.


  1. Love this article.

    I spoke to a 54 year old woman during an Olympic triathlon bike ride. We both said we never speak during a race but for some reason we introduced ourselves to each other, mainly so that we could communicate while leap frogging each other and not get caught drafting. It turns out she is training for the same 70.3 as I am and to top it off she is participating in the full FLA ironman in November as her A race.

    What she said stuck with me... "It keeps you young!".

    She placed in the female masters category.

  2. What about swimming speed (and/or endurance) and cardiovascular risk assessment?