Endurance training and cardiovascular health two sides to the story

Life is full of assumptions – I started my life as an athlete at the tender age of 10, at a time when I idolised my father who paddled in the Scottish kayaking Masters ranks, and when being good at sport kept the school bullies at bay.

I turned out to be one of the best young middle-distance runners in my country, so my goals were set for the Olympics from an early stage.

A number of years later, when I started studying exercise physiology, the American College of Sports Medicine (ACSM) guidelines were gospel: ‘exercise is good for our cardiovascular (CV) health’. This ‘knowledge’ was simply added affirmation to push on and train as hard as my body could cope with. My assumption, and that of most other athletes, was that if a certain amount of endurance exercise was good for our health, then super-elite athletes must be blessed with the best health. If somebody had told me at age 18 that consistent intense endurance training over many years could potentially be detrimental to my long-term health, I might have thought about my training differently. I was never one of these athletes who wanted to win at any cost – I would say that my health and physical fitness values were equally aligned.

The thing is though; the average subject in an exercise research trial is a young university student, and it is extremely easy to demonstrate improved CV health between sedentary and active individuals. Even if we look at research studies that centre around older individuals with CV pathology, if the researchers intervene and coach them from a sedentary to active state, they will almost always demonstrate improved CV health. And that has always been the message of ACSM and other health-related organisations: it is better to be active than sedentary.

However, for several years, I was training intensely seven days per week – hardly the definition of ‘active’ that ACSM was talking about – whose activity guidelines are actually fairly modest (1). It has taken me more than a decade into retirement from competitive running to start questioning whether intense and prolonged daily training is actually good for us. In the time that I’ve lived in Johannesburg, the land of extreme thinking, I’ve routinely interacted with recreational runners, cyclists, swimmers, and triathletes, who are undertaking large volumes of daily training (in addition to their work and family commitments) in pursuit of marathons, ultra-marathons, cycle stage races, and long-course triathlons. Those individuals who are quite new to this type of training regime often still look quite fresh and simply come to me to discuss race nutrition strategies. However, in those athletes who have been training this way for many years, often well into their 40’s and 50’s, I’m observing significant endocrine and immune dysfunction, often accompanied by signs of metabolic syndrome, including hyperlipidemia, insulin resistance, hypertension, atrial fibrillation, plus signs of oxidative stress and inflammation.  

Additionally, from what I’m about to share with you, I also now need to increase my referral rate for CV health assessments… In my quest to understand the other side of the CV health model in relation to endurance activity, I started a literature search recently – what I have learnt has shocked even me, in a way that I now need to share this with athletes and sports practitioners.

Multiple research studies are now implying that too much exercise may actually be detrimental to our CV health. I’ll start with an extremely comprehensive review by O’Keefe et al (2): after reflecting on all the highly beneficial effects of exercise, these researchers delved into a literature base that was studying the negative health implications of long-term consistent endurance training. They cited a study that had conducted MRI evaluations of 102 apparently healthy runners (aged 50-72), who had competed at least five marathons in the past three years (3). Evidence of patchy myocardial scarring was noted in around 12 per cent of these runners, which was a three-fold increased incidence compared to age-matched controls. Additionally, a German group of scientists observed a greater atherosclerotic burden in 108 middle-aged marathon runners compared to matched non-runner controls, as documented by higher coronary artery calcium (CAC) scores (4). What’s more, during follow-up, they ascertained that the adverse CV event rates in the marathoners were equivalent to those in a population with established coronary heart disease (4). I don’t know about you, but I’m extremely concerned with these findings in reference to all the recreational athletes that I look after - those people who are increasingly looking for longer and longer endurance challenges. One of the studies assessed runners who had completed five marathons over the past three years (3) – I regularly meet runners who use more than five marathons each year for ‘training’ sessions in the lead up to ultra-marathons, most notably the famous South African Comrades road race (89km). Then there are the athletes who complete Ironman and Comrades in the same year, and the events are only two months apart! And those people who are proud to complete 20 Comrades marathons in a row, often with extremely compromised musculoskeletal function.

Although scientists have still to agree on a common consensus when it comes to the CV implications of high volumes of endurance exercise, I feel that there is enough evidence to warrant asking athletes: are you training for long-term health or to feed a habitual behaviour of excess? As I do with historical eating patterns, if we look back to what our ancestors would have done, they would generally have been a lot more active than we are, but it would have been unlikely that they would engage in long-distance uninterrupted intensive exercise on a daily basis - walking would have been the main mode of movement, interspersed with short periods of running as and when required. Like many exercise-health relationships that have already been well researched, some researchers in this field are proposing a dose-dependent bell-shaped curve, where moderate exercise provides the best long-term CV health.

With these concerning observations in mind, we have a duty towards our more ‘experienced’ athletic clients to try and coach them towards moderation, and to support them nutritionally as much as possible to decrease the impact of training-induced oxidative stress and inflammation. I personally don’t think a few years of hard training will be detrimental to the average athlete’s health (or perhaps I’m in denial?!), but those individuals who push on year after year through their middle and older life periods require this information the most.


  1. Garber CE et al (2011). American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise. Med Sci Sports Exerc. 43(7):1334-1359.
  2. O’Keefe JH et al (2012). Potential adverse cardiovascular effects from excessive endurance exercise. MayoClinProc. 87(6):587-595.
  3. Breuckmann F (2009). Myocardial late gadolinium enhancement: prevalence, pattern, and prognostic relevance in marathon runners. Radiology. 251(1):50-57.
  4. Mohlenkamp S et al (2008). Running: the risk of coronary events; prevalence and prognostic relevance of coronary atherosclerosis in marathon runners. Eur Heart J. 29(15):1903-1910.