In the third year of my medical science degree, we covered a lot of exercise physiology. If I’d had the sense to do statistics in first or second year, I would have paid less attention to that part of my course, and written a certain literature review very differently.
Somewhat ironically considering the rampant success of Jenny Craig, exercise physiology and nutrition are, as far as I know, uniquely underfunded areas of medical research. Both are time and labour intensive – they require participants either to keep accurate, detailed records of their daily activities, or to attend a lab for several hours a week. These are things few people can or will do, and things which consume a significant amount of the researchers’ time in supervision. They also require things most people find unpleasant – strict diets, strenuous exercise, and the occasional muscle biopsy. As a result, it’s perfectly normal to see exercise phys studies with a sample size of five or ten participants, usually all of one gender, often of the same level of fitness. The studies themselves usually only last a few weeks; I don’t think I’ve seen one longer than two months. These things in combination radically limit both the statistical validity of any results they generate, and the applicability of those questionable results to the average person. This is turn leads to a preponderance of very strange opinions among academics in the field.
I once attended a lecture in which a muscle physiologist stated categorically that, “Any weight you can lift for more than eight reps does not cause an increase in muscle size”. This is objectively wrong. She would have known that if she had ever talked to a body builder, or heaven forbid, entered a gym and watched the jacked guys in the free weights section for half an hour (creepy, but entertaining and informative!). Instead, she’s spent the last thirty years reading studies which ran for two weeks, and embarrassing herself in front of undergraduates who actually work out. I suppose they couldn’t accommodate a gym in the ivory tower. Was anybody without a PhD under the impression that what happens in the first two weeks you go to the gym (usually nothing) reliably indicates what will occur if you keep going? No? Good.
I don’t know to what extent personal trainers and the like actually read exercise physiology literature, but the occasional thing does make it through. Tabata et al produced the best known study on high intensity interval training, in which one alternates between running or cycling like hell for a short period of time and spending another short period of time going at a much slower place. They used six very fit young men, and “Tabata Intervals” became a bit of a fad for a while in spite of the fact that only very fit people are actually physically capable of doing them in the first place, and everybody else would probably benefit about as much from a short jog. All of the papers I read for that lit review claimed that intervals are better for improving cardiovascular fitness than steady state cardio (ie walking or jogging), but the difference is minor and the samples are so small it’s impossible to take them seriously. No doubt bigger studies do occasionally come out from better funded institutions, but I personally don’t spend my time wading through acres of garbage to find them.
My advice to the scientifically minded when it comes to exercise, therefore, is this: If a twenty something staff member at your local gym tells you about this amazing study they read or heard about, smile politely and go about your business. If a fitness website does the same thing, move on. If you’re serious about losing weight, eat less sugar and do more exercise. Everything else is details, and it’s probably irrelevant until you’re at a certain baseline level of fitness. If you’re just starting out, don’t even join a gym if you don’t want to – just walk everywhere you can. I know people who have lost 20+ kilos with that method (though sadly, it took a lot longer than two weeks). If you’re serious about a specific sport, including weight lifting or body building, find the oldest, most experienced coach / trainer you can and do exactly as they say. Their successes will almost certainly be a self-selecting population, and you may not end up among them, but if they are coaching some obviously fit people, they are doing something right. And should you ever feel an urge to read the literature, I suggest a nice walk outside in the fresh air. Much better for you.