Stiff Legs, Compliant Arteries: How Marathon Training Helps the Heart

Healthy men and women training for and completing their first marathon experience significant reductions in central blood pressure and aortic stiffness, according to the results of new study.

Following a beginner’s training program, which included three runs per week that increased in difficulty over 17 weeks, led to an increase in proximal and distal aortic distensibility as assessed by cardiac magnetic resonance (CMR) imaging, and this improvement in aortic stiffness was equivalent to a 4-year reduction in arterial age, the researchers calculated.

“We know that as we get older, our blood vessels become less compliant, less elastic, and we get a stiffening of the vessels,” senior investigator Charlotte Manisty, MD (University College London, England), told TCTMD.

With age, there is a rupture of elastin fibers, deposition of collagen and calcium, and vascular smooth muscle cells become less functional, which leads to large artery stiffening, she said. “That, in itself, can lead to an increase in blood pressure, but we know that beyond the changes in blood pressure, increased stiffness with age increases the risk of cardiovascular events,” said Manisty. “Anything that can impact age-related aortic stiffening is likely to be positive for overall health.”

Past research has shown that long-term athletes have a “younger vasculature” than their sedentary peers, which suggests exercise could delay large artery stiffening, she said. Other studies have shown short-term, structured exercise programs have a positive effect on brachial blood pressure and peripheral artery stiffness. To date, though, there have been no “real-world” studies looking at the effects of exercise training on aortic stiffness.

Published January 6, 2020, in the Journal of the American College of Cardiology, with Anish N. Bhuva, MBBS (University College London), as lead author, the study included runners 18 to 35 years participating in the 2016 Virgin Money London Marathon and adults of all ages running in the 2017 race. In total, 138 first-time marathon runners (mean age 37 years; 51% women) were assessed at baseline, which was 176 days before the race, and at 16 days after the event. The training program was designed for first-time runners to complete the race, with runners averaging between 6 and 13 miles per week. The average finishing time was 5.4 hours for women and 4.5 hours for men.

After the marathon, central systolic and diastolic blood pressures decreased by 4 mm Hg and 3 mm Hg, respectively. The reduction in aortic stiffness was most pronounced in the distal aorta. There was no change in distensibility in the ascending aorta, but there was a 9% and 16% increase in distensibility in the proximal descending and diaphragmatic descending aorta. Because arterial stiffness can reflect changes in the arterial wall or the functional effects of loading conditions, the researchers also measured the β-stiffness index, a pressure-independent measure of arterial stiffness. These results were similar to their main findings.  

The increase in distensibility following the training program translated into a reduction in biological age by 1.5, 3.9, and 4.0 years in the ascending, proximal descending, and diaphragmatic descending aorta, respectively. Overall, older age and a slower marathon time was associated with a greater reduction in aortic stiffness. Men also had a greater reduction compared with women in the descending aorta β-stiffness index.   

Skeptical of Functional Changes

Benjamin Levine, MD (Institute for Exercise and Environment Medicine/UT Southwestern Medical Center, Dallas, TX), a cardiologist who has studied the cardiovascular effects of exercise training, said the 17-week training program with its end goal of completing a marathon or race is a worthwhile model to get people started with consistent physical activity.

However, he said he’s skeptical the short-term training stimulus led to structural changes. A decade ago, Levine published a small study showing that progressive and vigorous exercise training for 12 months did not favorably reverse arterial stiffening in sedentary seniors. In 2018, his group did show that four-to-five exercise sessions over more than 25 years was associated with reduced central arterial stiffness in older adults.

“I think what [Bhuva and colleagues] did was they reduced vascular resistance and lowered the blood pressure and that caused an apparent improvement in aortic distensibility,” Levine told TCTMD. “All those are good things—I don’t want to appear negative because I’m pleased they showed a nice reduction in blood pressure—but I think it would be an overstatement to state they truly demonstrated a structural change.”

In addition to lowering blood pressure, he said, exercise training improves endothelial function, reduces sympathetic activity, and decreases vascular resistance and these functional changes may appear to affect the distensibility of the aorta, specifically the distal aorta where there is greater resistance and sympathetic innervation.   

Julio Chirinos, MD, PhD (University of Pennsylvania Perelman School of Medicine, Philadelphia), who wrote an editorial accompanying the study, told TCTMD the elastin breakdown and calcification associated with aging is unlikely to reverse with a short-term exercise program. Regarding the findings, Chirinos wasn’t as skeptical of the results as Levine, noting there are potential biological mechanisms in which exercise can decrease aortic stiffness. 

The aorta is heterogenous in composition, he explained, with progressively more vascular smooth muscle cells and decreased elastin moving from the proximal to distal segments. Given the selective change in the more distal thoracic aorta segments in the present study, Chirinos said he suspects exercise may modulate vascular smooth muscle cell tone, which in turn modulates aortic stiffness. In his editorial, he notes that the change in descending aortic stiffness was partially independent of the change in pressure, “which suggests intrinsic changes in the material properties of the aortic wall, rather than simply changes in loading conditions.”  

For Chirinos, the real strength of the present study is that it’s a real-world, self-supervised setting that utilizes an inexpensive form of exercise.  

“It’s just one more reason why we should be encouraging physical activity, even in people who are sedentary and who may already have high blood pressure or other risk factors,” he said. Chirinos writes in his editorial that if the observed effect of exercise on large artery stiffening can be sustained, “[it] could have major effects on the myocardium, kidney, brain, and various other organs, with a potentially broad impact on age-related conditions.”

Clinical Implications  

Manisty said their interest was in studying the effects of exercise on the cardiovascular system in individuals who weren’t professional athletes, or elite, high-level performers. Additionally, the researchers did not want to study the effects of an expert-level training program, but instead something most people could tackle. For this reason, the group believes their results are generalizable to larger segments of the population.

“We were interested in what happens to normal individuals,” she said. “None of these people were athletes. They included a broad range of participants and the marathon completion time was very achievable. In fact, they were half an hour slower than average across the whole of the London Marathon. These are not people who were training excessively hard.”   

Regarding the clinical implications, Manisty said the study shows that even healthy individuals have a lot to gain from a relatively easy-to-implement exercise program. In addition to a younger vasculature, there was a 4-mm Hg reduction in brachial and aortic systolic blood pressure, which is in line with what could be achieved with a first-line antihypertensive agent, she said. “We’re not talking small or insignificant changes,” said Manisty.

To TCTMD, Levine pointed out the beginner’s training program didn’t involve a large amount of physical activity and did not translate into significant improvements in fitness, noting there was only a small change in peak VO₂. He noted that while the researchers opened the study up to patients of all ages, the vast majority of people were young.

“Even in the second group, the mean age was only 47 years,” he said. “They almost had nobody over age 60. These are young and middle-aged people. We’ve already shown in a number of circumstances that there is more plasticity to a variety of different training interventions in middle-aged adults than in seniors. The argument that ‘it’s never too late’ is not supported by the data they present, especially for structural changes in the heart and blood vessels.”