Endurance athletes – do they have more CV events?

25th March 2023, Dr Chee L Khoo

It’s not really an article you want to read at the eve of a major event. I am off to Paris this week for my second overseas marathon. My cardiologist thinks I am medically crazy to do a marathon at all. So far, I have kept up my side of the bargain by keeping my heart rate to the recommended maximal heart rate during my training (and mostly during the events). There have been previous studies on marathon runners. Overall, the cardiovascular event rates are still lower than that of the general population. A recent study in the European Heart Journal has thrown some doubt onto those rates. The question posed is “do long term endurance athletes have more coronary artery disease than similarly healthy non-athletes?”

The presence of coronary artery calcification and atherosclerotic plaques are strong predictors for future cardiovascular morbidity and mortality. Although, there is clear evidence that chronic physical activity and exercise training significantly reduce the risk for cardiovascular events (1), several recent studies have suggested that high-volume, high-intensity exercise training may actually increase the prevalence and severity of coronary atherosclerosis (2-4). To add to the confusion, the methodology to assess coronary atherosclerosis in the studies differ. Some use coronary artery calcification score (CACS) while others use coronary CT angiogram (CCTA) as their marker of significant atherosclerosis and they are not equivalent.

The variability in outcomes, in studies of the relationship between physical activity and CAC, may also be a result of the methods used to measure physical activity. Some studies use accelerometer while others use an exercise questionnaire to measure physical activity. The quality of questionnaires, whether past or current activity is measured, and if total activity or only intentional exercise is measured could also impact findings. Yet, others use cardiorespiratory fitness measures as a marker of physical activity. Cardiorespiratory fitness comprises a set of attributes that individuals inherit or achieve through exercise training that is measured by their ability to perform physical activity (5).

Exercise good or bad – the data

Regular physical activity and exercise improves cardiovascular risk factors including BP, serum lipids, glycaemic control, and cardiovascular function, but studies examining the relationship between physical activity and CAC is conflicting. Some have reported an inverse relationship (19–26). Some reported a positive relationship (6,7) while others report no relationship.

When cardiorespiratory fitness was used, several Korean studies found an inverse association between cardiorespiratory fitness and CAC among mainly middle-aged men (8-10). However, the CARDIA study (Coronary Artery Risk Development in Young Adults) found a positive association between cardiorespiratory fitness and CAC in young adults followed for 27 years which disappeared after multivariate adjustment (7).

Endurance Exercise Training

Most studies looked at general physical activities as marker of fitness although, as mentioned, some studies look at parameters which constitute cardiorespiratory fitness. What about endurance exercises? Endurance exercises include long distance running, bike riding and triathlon training

There have been many studies which have assessed the long-term effect of endurance exercise training on coronary atherosclerosis as assessed by CAC (11). In some, CAC is present in between 34% – 71% of athletic cohorts and 11% – 36% have CACS ≥100, a value often used to signify increased risk. A few studies found a higher prevalence of CAC among the most active athletes. Yet other studies revealed a greater prevalence of CACS ≥100 in more active subjects.

The Master@Heart study is the largest and most comprehensive study to assess the dose-response relationship between intensive endurance exercise and coronary atherosclerosis (12). 191 lifelong master endurance athletes, 191 late-onset athletes (endurance sports started after 30 yo), and 176 healthy non-athletes, all male with a low cardiovascular risk profile. Athletes were defined as endurance if they performed either >8 hours a week of cycling or triathlon or >6 hours a week of running.

Lifelong endurance sports 1.86X more likely to have ≥1 coronary plaque, 1.96X more likely to have  ≥1 proximal plaque, 1.58X more likely to have ≥1 calcified plaques, 2.07X more likely to have ≥1 calcified proximal plaque, 1.95X more likely to have ≥1 non-calcified plaque, 2.8X more likely to have  ≥1 non-calcified proximal plaque and 1.78X more likely to have ≥1 mixed plaque compared to a healthy non-athletic lifestyle. The late onset group had less plaque burden than the lifelong endurance athletes but were more than the healthy non-athletic group.

Well, we can’t claim that highly trained and fit athletes have a more benign plaque composition to explain their lower risk of cardiovascular events. Previous studies have reported that although healthy marathoners have higher CAC burden than non-athletes, the plaques were mostly calcified whereas the non-athletes had the more dangerous mixed plaques. This study did not agree with the more benign theory.

This study also reported that endurance athletes had less vulnerable plaques overall and the coronary stenosis was less. it is known that endurance athletes have larger coronary arteries and a greater vasodilatory potential, meaning that the plaque-to-vessel ratio in athletes could be lower and thus lead to less significant stenosis.(13,14).

The authors speculated that dose-response relationship between endurance exercise and coronary atherosclerosis might be reverse J-shaped rather than a descending logarithmic function. While a healthy lifestyle and above-average cardiorespiratory training and fitness prevents coronary atherosclerosis with a more favourable pattern of more calcified and less mixed or non-calcified plaques, further increments of endurance training add little to the benefits. A lifetime of training increases the overall atherosclerotic burden over time.

Potential explanations for the increase in coronary atherosclerosis

The exercise-induced increase in cardiac output may increase mechanical stress on the coronary vessel wall and disrupt laminar blood flow patterns, leading to vessel wall injury and accelerated atherosclerosis.52 High blood pressure may accelerate coronary atherosclerosis,53 and because systolic blood pressure increases during exercise, this may contribute to accelerated atherosclerosis. The finding that very vigorous exercise was associated with atherosclerotic plaque and CAC prevalence fits with this hypothesis because the most intense exercise is associated with the greatest increases in both heart rate and systolic blood pressure. Running induces a large pressure concussion wave during foot strike, which alters coronary haemodynamics and could accelerate coronary atherosclerosis. This effect is also dependent on the timing of steps during running with reference to the cardiac cycle.

In summary, too much of a good thing can be harmful. There are more research to do yet to tease out whether endurance training does increase cardiovascular events. Longitudinal research is needed to reconcile these findings with the risk of cardiovascular events at the higher end of the endurance exercise spectrum. I think I can still go to Paris.


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