Recreational Marathon Training: Good for Runners’ Hearts

A NEW study–the first to look deeply into heart-related changes that result from typical midpack marathoner training–provides much good news for runners logging 40 to 50 kilometres a week. The study published in the American Heart Association journal, Circulation: Cardiovascular Imaging was conducted by cardiologist Aaron Baggish, M.D., and colleagues in Boston. Baggish, co-medical director of the Boston Marathon and a multi-time marathon finisher himself, is rapidly becoming one of the foremost investigators into the heart health of marathoners.

Baggish summarised the study to Runner’s World US as follows: “In a nutshell, recreational marathon training is healthy no matter what metric you look at. There was nothing we saw that could potentially link training to adverse health outcomes.”

Prior studies of runners have tended to fall into two categories. First, you’ve got your case studies of elite athletes such as Zersany Tadese, the half marathon world record holder. These prove that top runners have astonishing physiologies but don’t tell you much about yourself.

Second, you’ve got your “big data” studies, such as those showing cardiac arrest mortality risks in marathon racing at about 1 in 200,000+ runners. That’s a lot of runners, so again you don’t learn much about yourself.

To learn more about typical runners, Baggish and his team followed 49 male recreational marathoners as they amped up their training for the 2013 Boston Marathon. The researchers wanted to see what happened to these runners during an 18-week period when they increased their training from 25K a week to a high end of 50K a week. The training program, included a long run of 35K three weeks before the race. During the 18-week period, runners averaged about 40K per week.

The results? While you might never run in the Olympic marathon, your modest marathon training produces cardiac and fitness benefits similar to those found among Olympians. “A recreational running program is sufficient to stimulate both the structural and functional cardiac changes that have previously been documented among elite competitors,” wrote Baggish and his coauthors in the study.

Of the 49 study subjects, average age 47, four dropped out of the program with injuries while the rest completed the program and ran the marathon. The researchers put all runners through a series of heart size/function tests, treadmill tests, and blood tests before and after they began their marathon-training buildups. Baggish hoped to correlate the runners’ training data with their marathon finish times, but the 2013 bombings prevented many from reaching the finish.

Roughly half of the runners were “less experienced,” with an average of one prior marathon completion and a best time of 4:16. Half were “more experienced,” with an average of 14 prior marathons, including a best time of 3:43.

The investigators wanted to see if the two groups differed in any substantial ways, but they found only very small differences–nothing they deemed significant. The experienced runners were older, shorter, weighed less, and drank more alcohol than the less experienced runners. Both groups had the same BMI, and both groups showed similar adaptations on almost all tests. (See the table below for more “pre-training” and “post-training” data on the runners in the study.)

Here are the study’s main findings, along with comments provided by Baggish.

1: Marathon training led to improvements in exercise capacity and exercise performance, and favorable changes in several biochemical markers (for example, low density cholesterol and triglycerides) of cardiac disease risk.
“Recreational marathoners can go for it and have fun with their marathon goals (after of course talking to a knowledgeable healthcare provider who understands both medicine and marathoning). There is nothing but good things that come from normal marathon training.”

2: Marathon training led to the enhancement of LV diastolic function.
“Runners and others with LV diastolic dysfunction have impaired relaxation of the heart in between beats to accept blood filling. This is the most common underlying reason for heart failure. So anything that gets rid of LV diastolic dysfunction is hugely beneficial.”

3: Marathon training led to cardiac remodeling characterised by LV dilation, RV dilation, and left atrial dilation, often beyond normal values.
“These are identical to the changes seen in elites. They all have adaptive explanations and are not in any way linked to pathology.”

Baggish counts himself among those skeptical of recent reports of the risks of excessive exercise, including marathon training. He believes there is no convincing data to support such a conclusion.

“The last two JACC [Journal of the American College of Cardiology] publications show nicely that some exercise is better than none, but they have done major (and scientifically embarrassing) damage to views about higher level exercisers,” he says. “While there are very likely no additional health benefits from pushing beyond moderate levels of exercise, this does not mean that more is worse. Our paper shows that the exercise routines followed by most runners are very unlikely to be an issue for concern. There is likely a tiny minority who can overdo things, but this minority really is tiny.”

Key changes exhibited by 45 middle-age male marathoners (average age, 47) who trained for the 2013 Boston Marathon for 18 weeks.

Pre-Training Post-Training
VO2 Max 44.6 ml/kg/min 46.3 ml/kg/min
Treadmill Test 16.7 mins 17.2 mins
Fasting Glucose 91 mg/dL 92 mg/dL
CRP 1.9 mg/L 1.8 mg/L
Creatinine .98 mg/dL .91 mg/dL
Total Chol 199 mg/dL 192 mg/dL
LDL 120 mg/dL 114 mg/dL
HDL 55 mg/dL 55 mg/dL
Triglycerides 100 mg/dL 85 mg/dL


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