Exercise
I see optimized mitochondria function as the key to health (1).
When I discuss our work in metabolic neurology, I emphasize the absolute importance of dietary lifestyle over any other component of health, including exercise. I do this for a very logical reason - in terms of the modern lifestyle, nothing has changed as much as dietary lifestyle has over the last 50ish years. There are two main changes. First, the introduction of extra meals and snacks throughout the day, such that the average person now eats 5-6 times a day (1). Essentially, a loss of fasting. Second, the introduction of excess processed carbohydrates into the diet, such that the average person now eats about 10% less fat than they did in the 1970s, which has been replaced by processed carbohydrates (2). Essentially, a loss of fat. These changes in modern dietary lifestyle represent the strongest correlate of the rise of the lifestyle disorders over the past 50ish years, the most dominant of which are atherosclerosis, cancer, neurodegenerative disorders, and the metabolic syndrome (1).
Compared with our 2-3 million years of existence in the hunter-gatherer lifestyle, or even that in the last 50 years, nothing has changed as much as dietary lifestyle, the main driving force behind mitochondria dysfunction.
However, an unhealthy exercise lifestyle is also a barrier - not just too little, but also too much. If we take the more extreme case of ultra-athletes (who are mostly runners), these people often have problems occurring throughout their body both during and for several hours or days after any event, which include pathological changes in the heart, skeletal muscles, kidneys, and immune and endocrine system (4). Moreover, 50-60% of these athletes are plagued by musculoskeletal problems after the event, and a number of them have upper respiratory tract infections, digestive problems, and gastrointestinal bleeding after the event (4). However, these are not the main health problems experienced by ultra-athletes.
The real problems ultra-athletes face are their long-term health concerns, defined as those lasting 1 year or longer to the point they require ongoing medical attention, or limit activities of daily living, or both (5). These long-term problems occur in multiple body systems - cardiovascular, respiratory, musculoskeletal, renal, immunological, gastrointestinal, and even neurological (5). The most pronounced abnormalities occur in the heart, notably right ventricle enlargement and potential scarring leading to right ventricule dysfunction and arrhythmias, the kidneys, including a potentially accelerated progression of chronic kidney disease, and the musculoskeletal system, which includes accelerated hip and knee osteoarthritis, as well as tendon injuries. |
This is atherosclerosis, also commonly known as "hardening" of the arteries (6). |
Arguably, the most concerning effects of exercise in athletes are shown by multiple studies that collectively demonstrate competitive endurance athletes (not necessarily ultra-athletes, and again mostly runners) have more coronary artery calcification compared with recreational athletes (7) and even sedentary non-athletes (8). Higher coronary artery calcification is a problem, as this indicates the presence of atherosclerosis, or "hardening" of the arteries, which leads to nearly all heart attacks and a large number of strokes and is thus the most common cause of death in the west today. Moreover, a very recent study recently showed that athletes who exercise at a "vigorous" or "very vigorous" intensity actually show a progression of their atherosclerosis (9).
What does this mean? Should we exercise at all? If we should, how should it be done?
Measuring Metabolic Output
Before exploring the ideal exercise regimen for health, we need to discuss and define the concept of Metabolic Equivalents of Task (METs), as this is how most studies measure exercise output. For ease of conceptualization, a MET may be defined as the ratio of the rate at which a person burns energy while performing some specific physical activity compared with the rate at which they burn energy when sitting quietly (10). For an even easier conceptualization, a MET is simply the metabolic cost of a physical activity. There exists a compendium of physical activities that shows the MET scores for various activities (I have referenced an older but freely available version below) (11).
Using METs, physical activities can be classified by intensity. Light intensity activities are those that require <3 METs and include things like working at a desk, walking slowly, and fishing. Moderate intensity activities cost 3 to 6 METs and include things like yoga, walking quickly, and sweeping a floor. Vigorous intensity activities cost 6 to 9 METs and include things like basketball, slow running, and carrying groceries upstairs. Very vigorous intensity activities are those that demand >9 METs and include things like skipping, fast running, and active scuba diving (as opposed to just floating in one spot).
METs allow all physical activity to be standardized and compared, but there are major limitations to their use. First, the METs for each activity described above are those that were determined from a 40-year-old man weighing 70 kg, so for anyone who is not that, the numbers may somewhat differ. Second, there are also inherent problems in defining what is light, moderate, vigorous, or very vigorous activity from one person to the next - what one person thinks is vigorous may differ from what another thinks is vigorous, and each will therefore think they are burning the same number of METs when they are not. But the third and most problematic issue of the METs concept is that it simply looks at one parameter, that of energy output, or calorie-burning, without considering the real benefits of exercise, which relate to fitness and include improved strength, speed, and endurance. |
Classification of Metabolic Equivalents of Task (METs). |