Physical Activities – can one get overdose?

Introduction

“If exercise could be packed in a pill, it would be the single most widely prescribed and beneficial medicine”.
—Robert Butler, MD


Many observational studies have shown that regular physical activities improve many disease outcomes. They include cardiovascular disease, high blood pressure, diabetes mellitus, osteoporosis, obesity, colon cancer, breast cancer, anxiety and depression. Furthermore, large-scale prospective observational studies have also demonstrated a dose-response relation between the amount of physical activity and the risk of cardiovascular disease and premature mortality in men and women.


As such, in 2020, the World Health Organisation (WHO) made the recommendations that adults should do at least 150–300 minutes of moderate-intensity aerobic physical activity or at least 75–150 minutes of vigorous-intensity aerobic physical exercise or an equivalent combination of moderate- and vigorous-intensity activity throughout the week. Not stopping at this, WHO further recommends muscle-strengthening activities at moderate or greater intensity that involve all major muscle groups on two or more days a week. Exceeding the minimum recommended amount of physical activity would bring additional health benefits.
Moderate-intensity activities are generally equivalent to a brisk walk with a noticeable increase in heart rate. In contrast, vigorous intensity is typified by jogging, which causes a significant increase in heart rate and rapid breathing.


So, exercise is good, but can one get too much of a good thing or exercise overdose?
-Cardiovascular changes in physical training

Different forms of exercise impose differing loads on the cardiovascular system; pure endurance sports (e.g. long distance jogging) tend to place a high dynamic (isotonic) load on working muscles, and pure strength sports (e.g. weight lifting) place a high static (isometric) load on the muscles.

Cardiac adaptations/remodelling may happen in individuals who do high-intensity physical activities regularly; ECG changes include slow heart rate, first-degree atrioventricular (AV) block, incomplete right bundle branch block, early repolarization and QRS amplitude fulfilling left ventricular hypertrophy (LVH) criteria. The cardiac morphological changes would include increased cardiac mass, enlargement in heart size (more prominent in endurance sports), increase in heart wall thickness (more pronounced in weight training) and increased left and right atrial sizes. These structural and electrical changes are termed ‘athlete heart’ or exercise-induced cardiac remodelling.

In general, these changes are considered physiological adaptations. The changes would usually regress upon cessation of training, though longstanding changes in older athletes may not regress as effectively or entirely as in younger athletes.

However, as ECG changes, cardiac chamber dilatation and cardiac wall thickening are also seen in pathological conditions like heart muscle disease (cardiomyopathy). The physician must make accurate diagnoses to avoid over or under-diagnosis when seeing active individuals with cardiac abnormalities.


Adverse remodeling

Rhythm abnormality, or more specifically, atrial fibrillation (AF), is the most common cardiovascular problem athletes encounter. The frequency of AF has been estimated to be 2 to 10 times greater in high-intensity endurance athletes versus sedentary individuals. Possible postulated mechanisms are increased autonomic tone, atrial wall inflammation/fibrosis, and increased in atrial size. However, on the other hand, regular mild to moderate-intensity exercise protects from cardiovascular disease and AF. Premature ventricular contractions (PVCs) are also quite common in the athletic population.

Middle-aged and older male athletes have also increased coronary artery calcification (CAC) and atherosclerotic plaques, which were related to the amount and intensity of lifelong exercise. The cardiovascular risk associated with coronary atherosclerosis in athletes and how it differs from the general population is still uncertain.


Conclusion
Chronic physical training is beneficial most of the time to a large majority of people. However, adverse cardiac remodelling may happen in specific individuals who perform regular, intense exercise, and this is associated with an elevated risk of atrial and ventricular arrhythmia.


Nevertheless, in the current era, when physical inactivity and its associated risks are prevalent, the benefit of promoting and participating in physical activities exceeds any excess risk of arrhythmias.

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