How Much is Too Much?
A daily routine of physical activity is highly beneficial in the prevention and treatment of many prevalent chronic diseases, especially of the cardiovascular (CV) system. However, chronic, excessive sustained endurance exercise may cause adverse structural remodeling of the heart and large arteries. An evolving body of data indicates that chronically training for and participating in extreme endurance competitions such as marathons, ultra-marathons, Iron-man distance triathlons, very long distance bicycle racing, etc., can cause transient acute volume overload of the atria and right ventricle, with transient reductions in right ventricular ejection fraction and elevations of cardiac biomarkers, all of which generally return to normal within seven to ten days. In veteran extreme endurance athletes, this recurrent myocardial injury and repair may eventually result in patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, potentially creating a substrate for atrial and ventricular arrhythmias. Furthermore, chronic, excessive, sustained, high-intensity endurance exercise may be associated with diastolic dysfunction, large-artery wall stiffening, and coronary artery calcification. Not all veteran extreme endurance athletes develop pathological remodeling, and indeed lifelong exercisers generally have low mortality rates and excellent functional capacity. The aim of this review is to discuss the emerging understanding of the cardiac pathophysiology of extreme endurance exercise and make suggestions about healthier fitness patterns for promoting optimal CV health and longevity.
Dose of physical activity and all-cause mortality reduction. The mortality benefits of exercise appear with even small amounts of daily exercise and peak at 50 minutes of vigorous exercise.
Mortality and Running Speed
Risk Stratification of Endurance Athletes
Currently, we have no proven screening methods for detecting the CV pathology associated with EEE. A logical strategy for now would deploy post-competition cardiac biomarkers, echocardiography, and/or advanced imaging such as CMR to identify individuals at risk for and with subclinical adverse structural remodeling and the substrate for arrhythmias.61 For any individual who is considering EEE efforts such as marathons or day-long aerobic races for any other activity that elevates cardiac output for a sustained period (continuously over several hours), it may be reasonable to obtain a maximal treadmill exercise test to screen for ischemia and/or exercise-induced arrhythmias and Heart CT for CAC scoring, particularly for those who are over age 50 and who have been chronically training for and competing in EEE events. Aortic pulse wave velocity could give an inference into the development of vascular stiffness that may not be readily appreciated by cuff blood pressure measurement.
Avoiding Exercise-Induced CV Damage
Suggestions for an exercise routine that will optimize heath, fitness and longevity without causing adverse cardiovascular structural and electrical remodeling:
Avoid a daily routine of exhaustive strenuous exercise training for periods greater than one hour continuously. An ideal target might be not more than seven hours weekly of cumulative strenuous endurance ET.1,2,9,51
When doing exhaustive aerobic ET, take intermittent rest periods (even for a few minutes at an easier pace, such as slowing down to walk in the middle of a run). This allows the cardiac output to normalize temporarily, providing a ‘cardiac rest period’ when the chamber dimensions, blood pressure, and pulse come down closer to baseline resting parameters before resuming strenuous exercise again.2
Accumulate a large amount of daily light-to-moderate physical activity, such as walking, gardening, housekeeping, etc. Avoid prolonged sitting. Walk intermittently throughout the day. Look for opportunities to take the stairs. 1, 2 Buy a pedometer and gradually try to build up to 10,000 steps per day.
Once or twice weekly, perform high-intensity interval exercise training to improve or maintain peak aerobic fitness. This is more effective in improving overall fitness and peak aerobic capacity than is continuous aerobic exercise training, despite a much shorter total accumulated exercise time spent doing the interval workout.65, 66
Incorporate cross-training using stretching, for example, yoga, and strength training into the weekly exercise routine. This confers multi-faceted fitness and reduces the burden of cardiac work compared to a routine of daily long-distance endurance exercise training. 1, 2
Avoid chronically competing in very long-distance races, such as marathons, ultra-marathons, Iron-man distance triathlons, 100-mile bicycle races, etc., especially after age 45 or 50.
Individuals over 45 or 50 years of age should reduce the intensity and duration of endurance exercise training sessions, and allow more recovery time.
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