Examining the Controversy: Is too much exercise bad for the heart?

swimming in triathlon  

The mainstream media claims recent research may show vigorous exercise is unhealthy. That isn’t the complete picture.



A flurry of studies  a few years ago suggesting too much exercise is detrimental to one’s health sparked fierce debate over the legitimacy of the claims. The mainstream media jumped into the fray. The Wall Street Journal published an article “One Running Shoe in the Grave” arguing too much exercise stresses the heart enough to erase any physical activity health gains. What did the studies actually find, and is it a cause for concern?

One study tracking 52,000 adults for 15 years found that runners had a 19% decrease in all-cause mortality. However, when it was broken down by mileage a U-shaped curve emerged. Those exercising moderately for 2-5 days a week had the lowest mortality. The extremes had the highest mortality. In fact, the people running more than 25 miles a week had almost as high a mortality rate as those not exercising at all. The figure below shows this “U-curve” from the study (Running and all-cause mortality risk: is more better? 2012. Lee J, et al.)

However this does not give the complete picture. Another study, published in 2011, found that vigorous exercise and moderate exercise had differing amounts of benefit towards reducing mortality risk. The authors found that moderate exercise showed a gentle, increasing curve when plotted against mortality risk.  Meanwhile, vigorous exercise had far higher marginal returns up to about 50-60 minutes a week when it began to plateau. For both vigorous and moderate exercise, diminishing returns was observed as expected. However, no negative relationship was seen with extreme durations of daily exercise. The relationship can be seen in the figure below (Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study, 2011. Wen CP, et al.)

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So although the relationship cannot be fully established, if vigorous exercise does cause an increase in mortality risk past a certain point what is the cause?  According to a review by cardiologist James O’Keefe and colleagues, the cause is a problem with heart function.  (Potential Adverse Cardiovascular Effects From Excessive Endurance and Exercise, 2012.  James O’Keefe, et al.). Athletes develop an enlarged left ventricle to enable increased circulation. This remodeling does not disappear for at least several years following retirement from vigorous exercise. Several biomarkers for myocardial damage appear to be elevated following intense, prolonged races such as triathlons or marathons.  Myocardial scarring from vigorous exercise may lead to problems. Endurance athletes have been shown to have a higher rate of electrocardiogram problems.  Endurance athletes may have a five-fold increase in prevalence of atrial fibrillation. The increase in atrial size from endurance training may be responsible for atrial fibrillation.

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Other problems with the cardiovascular system that show up in endurance athletes include coronary artery calcification, diastolic dysfunction, aorta wall stiffening and myocardial fibrosis. Despite all these potential problems the authors add that lifelong vigorous exercisers generally have low mortality and great cardiovascular function; its an interesting paradox.

In conclusion, if health is your sole reason for exercising it may be best to limit exercise to 2-5 days a week of moderate exercise. However, the risks of vigorous exercise are highly speculative until more research comes out. The mainstream media is likely exaggerating the findings of recent studies or drawing hypothetical conclusions. When carefully looking at the data and the papers collectively, the research says vigorous exercise is still good for the body. Regardless of which side ultimately wins the debate, exercise is undoubtedly good for the mind and collective well-being.

Playing on Turf increases Injuries in the NFL


A recent study found that NFL games played on turf showed significantly higher rates of lower-leg injuries.



Across sports and competition levels, playing surfaces have been switching from natural grass to artificial turf. This has several health ramifications. Some researchers have speculated that the rubber polymers used in artificial turf cause cancer. Although turf’s carcinogenic properties have not been proven, a recent study of NFL players showed that the incidence of knee and ankle injuries is significantly higher in games played on turf.

The first NFL stadium to use an artificial playing surface was the Houston Astrodome in 1966. The surface, called AstroTurf, was manufactured by Monsanto and consisted of a padded-carpet over asphalt. In the 1990’s infill surfaces became popular and are widespread today. Infill surfaces consist of an interwoven mat of polyethylene fibers filled with rubber particles. The frequency of NFL games played on turf has been increasing over the years as more NFL stadiums adopt turf. The figure below demonstrates this trend over the previous decade.

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Several studies have looked at injury rates in football players based on field surface. A study done in the early 2000s found that ACL injury rates of high school players are higher in games played on turf. However, the same study found college players were more likely to sustain an injury on grass than turf. A recent study looked at several different lower leg injuries in NFL players using extensive data collected by the injury surveillance system maintained by NFL trainers (An Analysis of Specific Lower Extremity Injury Rates on Grass and FieldTurf Playing Surfaces in National Football League Games : 2000-2009 Seasons; 2012. Elliot B. Hershman, et al.). The study used data from NFL seasons from 2000 to 2009.

The aforementioned study looked at several different lower leg injuries in NFL players: knee sprains, MCL and ACL injuries, ankle sprains, inversions and eversions. Although all injury categories demonstrated a higher frequency in turf than grass, MCL (median collateral ligament) injuries and inversions (an ankle sprain where the ankle is twisted inwards) both did not show significance. The injuries that did show significantly higher prevalence on turf were knee sprains, ACL injuries, ankle sprains and eversions. The figure below shows the injury rates in NFL players based on a density ratio of turf over grass injury rates.

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ACL sprains occurred at a rate 67% higher on turf than grass. Eversion ankle sprains occurred at a rate 31% higher on turf than grass. Despite the significantly higher rates of injury on turf, this study was limited because it did not suggest any mechanisms by which turf causes higher lower-leg injury rates nor a means to make artificial surfaces safer.

The Physiology of Icing Sore Muscles

meb marathon new york


Meb Keflezighi (left, winning the 2009 NYC marathon) credits much of his success to icing.



About a year ago I met Meb Keflezighi, one of the greatest American marathon runners of all-time, while training at Mammoth Mountain in California. Since then the 37 year-old stud has had a very successful season culminating in a fourth place finish at the 2012 London Olympics. During our meeting he stressed the importance of icing on his success. Therefore, I was not too surprised that Meb emphasized his devotion to icing during media interviews after winning the 2012 American Olympic marathon trials. Meb is unquestionably one of the world’s most elite marathon runners. However, the question remains: What part has icing played on Meb’s running career?

Although studies looking at the effects of icing, or cryotherapy, have had somewhat conflicting results, most studies have found icing following exercise-induced muscle damage to be beneficial. The extent of muscle damage peaks between 24 and 72 hours following strenuous exercise. Exercise-induced muscle damage includes sarcolemma disruption, fragmentation of the sarcoplasmic reticulum, lesions of the plasma membrane cytoskeletal damage and swollen mitochondria. Outside the muscle fiber there may be swelling due to an increase in blood flow and capillary permeability.

One study looked at the multi-day effects of icing on exercise-induced muscle damage (Effects of cold water immersion on the symptoms of exercise-induced muscle damage, 1999, Roger Eston and Daniel Peters). The study used 15 female subjects and endurance exercised their biceps. The cryotherapy group submerged their exercised arm into a tub of 15 degrees Celsius  water for 15 minutes. This treatment was administered immediately after the bout of exercise and every 12 hours thereafter for 3 days.

The study results show that creatine kinase activity, a predictor of muscle damage, was lower in the cryotherapy treated group two and three days after the bout of exercise. The graph below shows these results.

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Eston and Peters also showed that the arm circumference and tenderness were not significantly affected. However, arm strength returned to baseline much faster in the cryotherapy group. This is of particular interest to athletes who often are expected to complete consecutive workouts in a 72 hour timeframe.  The difference was significant: after 72 hours the control group had a mean isometric strength that was 86% of baseline while the cryotherapy group had a mean isometric strength that was 111% of baseline.

A more recent study on the subject of icing measured blood flow, temperature and muscle endurance in cryotherapy treated and control groups (Changes in Blood Flow, Temperature and Muscle Endurance in Association with Cryotherapy, 2009, Masahiro Utsunomiya, et al.). In this Japanese study three groups were established: resting group (10 minute rest), 2-minute cooling group (2 minute icing and 8 minutes of rest) and 10-minute cooling group (10 minutes of icing).  Endurance was significantly boosted by icing. After ten minutes of rest the resting group performed at 59.2% of the initial test, the 2-minute cooling group 73.1% of initial test and the 10-minute cooling group 80.7% of the initial test. This suggests that the effects of icing are immediate.  Decreases in deep part temperature and tissue circulating volume were also observed as duration of icing increased.

The authors suggested that the cooling decreased oxygen consumption and cellular metabolism. This would potentially increase muscle endurance.  However,  an EMG signal processed with Fast Fourier Transformation saw no significant differences between the groups during the second bout of training. The authors hypothesized that the lack of significance means differences in endurance could have been the result of lowering myogenic pain instead of an increase in physiological fatigue.

The Running Mechanics of Elite African and Caucasian Marathoners

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Ryan Hall, one of the greatest marathoners not of African descent. Although his form contributed to his running efficiency, he was forced into retirement from injuries.


The mechanics of the perfect running form we should all strive for…


An interesting video comparing the running mechanics of some of the fastest African and Caucasian marathon runners including Ryan Hall and Meb. Meb is still chasing medals in the 2016 Rio Olympics, while Ryan Hall retired after injuries derailed his career. This video offers suggestions for enhancing performance and preventing injuries. Brought to  you by Somax Performance Institute, a renowned sports science center just north of San Francisco. Enjoy!

Despite Increased Participation, Marathon Mortality Remains Constant

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Marathon participation has been growing swiftly over the last decade. Despite the increase in participants (including “ridiculously photogenic guy” 10k finisher to the right), mortality rate has not increased while average finish time has improved.


The marathon has seen tremendous growth in participation over the last decade. As the figure below shows, the number of marathon participants has soared from 299,000 participants in 2000 to 475,000 in 2009. This growth has been ruled in part by an increase in awareness of the benefits of running, many of which have been reported on this site. Despite the health benefits, one study found that 90% of marathon participants reported suffering a musculoskeletal or other participation-related injury prior to or during the marathon (Mortality Among Marathon Runners in the United States, 2000-2009. Published 2012. Simon C. Mathews, et al). In addition, the media has reported on several high-profile marathon deaths.

It might be supposed that given the increase in participants, mortality rate in marathon participants might rise due to a greater proportion of unqualified runners.  A recent study found this not to be the case. In fact, not only have mortality rates remained constant over the last decade (as the figure below depicts), but average finish time has slightly decreased.

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The rate of mortality remains slightly higher in males than females. The median age of mortality was 41.5 years old. The average distance completed before death was 22.5 miles. The most common cause of death among participants 45 years or older was myocardial infarction or coronary atherosclerosis (a heart attack). For younger participants the most common cause of death was cardiac arrest. Interestingly, participants who died within 24 hours of completing the marathon had an average finish time below the average of all marathon finishers. This suggests that physical fitness does not predict risk of marathon mortality, although it may be a sign of overexertion.

In conclusion, mortality rates in marathon finishers remains very low. Over the last decade there was 0.75 deaths per 100,000 finishers.  By comparison, motor vehicle fatalities represent 11.2 deaths per a population of 100,000.  Only 28 deaths of marathon participants during or in the 24 hours following their race have been reported in the last decade. This is an indication of the rarity of marathon fatalities, and also the limits of drawing demographic conclusions on the basis of such a small sample size. Marathon mortalities prevalence in the media is the result of several high profile incidents. Overall marathon running is safe regardless of age or physical fitness.

ACL injuries in Female Skiers

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A new study finds that females, but not males, show a higher risk of ACL injury in their nondominant leg while alpine skiing. 


A new study out of Austria found that female, but not male, alpine skiers show a significantly higher risk of ACL injury in their non-dominant leg (Leg Dominance Is a Risk Factor for Noncontact Anterior Cruciate Ligament Injuries in Female Recreational Skiers; 2012, Gerhard Rued, et al.).

Knee injuries account for a third of all reported skiing injuries and half of these knee injuries are due to an Anterior Cruciate Ligament (ACL) injury. Disparities exist between genders. Female recreational skiers’ ACL injury risk is three times higher than their male counterparts.  Females tend to be more one-leg dominant, suggesting a possible link between leg dominance and ACL injury risk.

The aforementioned study surveyed intermediate to expert recreational skiers suffering from ACL injury at an Austrian ski clinic. The skiers were all in good physical condition at the time of the accident. Female skiers suffered an ACL injury in their non-dominant leg 63% of the time. By comparison, only 45% of male skiers suffered ACL injuries in their non-dominant leg.

The surveys gathered information on when the ACL injury occurred in the skiers.  Most left-leg ACL injuries occurred while making a right turn. During a right turn a majority of the weight is on the outer leg (the left leg in a right turn) as pressure is placed on the inner edge of the outside ski to sustain the turn. The authors proposed altering ski boot design so that less stress is placed on the knees while carving turns.

Interestingly, soccer players follow similar gender patterns in ACL injuries. One study found that 68% of ACL injuries in female soccer players occur in the nondominant leg (the favored support leg during a kick) compared with 26% of ACL injuries in males (Gender influences: the role of leg dominance in ACL injury among soccer players, 2010; Brophy R, et al.). The physiological reasons for the gender disparity in ACL injuries in both soccer players and alpine skiers remains unknown.

If you, or someone you know, suffered from an ACL injury while skiing or playing a sport let me know via email (contribute@exercisemed.org) or leave a comment.

Mechanics of Ankle Sprain in Runners

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Research shows that individuals who do and do not develop chronic ankle instability after an initial ankle sprain have different running kinematics.


Ankle sprains are a common injury for runners. Generally, ankle problems persist after an individual sprains their ankle. Ankle instability following an initial sprain is called chronic ankle instability (CAI). Two types of chronic ankle instability are possible: mechanical instability and functional instability. Both types of chronic ankle instability are characterized by complaints by individuals of their ankles giving way, but individuals with mechanical instability display lax lateral ankle ligaments. A study published in the August 2011 issue of the Journal of Sports Medicine looked at the mechanics of individuals who suffered from chronic ankle instability, both functional instability and mechanical instability, as well as individuals who suffered  from an ankle strain, but were lucky enough not to develop chronic ankle instability. Individuals who managed to avoid developing chronic ankle instability after an ankle sprain were appropriately labeled “copers” (Foot clearance in walking and running in individuals with ankle instability, 2011, Cathleen Brown).

The study found that individuals with chronic ankle instability had a lower minimum metatarsal height during the terminal swing. A graph comparing the metatarsal heights of copers, individuals with mechanical ankle instability and individuals with functional ankle instability as a function of time can be seen below.

Metatarsal height of copers compared to individuals with functional ankle instability and mechanical ankle instability during running.

Individuals with a lower foot height while running should see more ankle strains due to inadvertent toe strikes that would result. The individuals suffering from mechanical ankle instability had a significantly higher external foot rotation than the functional instability and coper groups. The mechanical instability group was found to be less plantar flexed during foot contact and were less everted.  Differences in gait were also found. The copers had far less frontal gait, possibly a sign of more control in their stride.

Similarly, differences were seen in the mechanics of the copers and chronic ankle instability suffering individuals while walking. The copers had less external foot rotation than the individuals suffering from chronic ankle instability. However, no significant difference was found in dorsiflexion while walking.

The results here are preliminary, only 11 male individuals were in each cohort. Thus, the study did not have much statistical power. However, the results do suggest that rehabilitation for individuals suffering from ankle strains can focus on the kinematics of their running or walking.