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Body by Science is a book, co-authored by medical doctor Doug McGuff and bodybuilder John Little, which proposes something that sounds too good to be true: "A research-based program for strength training, bodybuilding, and complete fitness in 12 minutes a week."
What Lies Behind This Claim?
Doug McGuff claims that Body By Science is research-based, and cites studies throughout the book to back up his central thesis: that physical adaptation is about fatigue at the cellular level. The idea is simple. First you need a sufficiently strong signal to the organism that it needs to adapt, and then you need sufficient time for that adaptation to take place.
The signal has to be sufficient that it fatigues muscle cells, which perhaps explains why bodybuilders use sets to failure with such effect. By this logic, a larger set is simply a way to achieve fatigue more slowly and gradually. By contrast, Dr. McGuff proposes a single set for each exercise, lasting about 2 minutes at the most.
Dr McGuff doesn't seem to be all that interested in "recovery", which is largely a CNS phenomenon.
As he explains, the signal needs to be panic-inducingly intense so that your body feels the need to adapt rapidly in order to keep you alive. But this adaptation takes time. Growing new muscle isn't a fast process and it's not metabolically cheap either. Even if you're already eating a lot, it's surprising how much food is required to build new tissue. The figures we have are necessarily vague but roughly speaking, each new pound of muscle tissue contains just under 4 ounces of protein, with most of the rest of its weight being accounted for by glycogen and water. However, it costs much more than the 450 or so calories this represents to actually synthesise the amino acids necessary for the new tissue and then to build it. One figure that gets bandied about a lot is that it costs 3500 calories to build a pound of new muscle. Others disagree, but with different metabolisms, training schedules and diets, plus the majority of the data relying on self-report, the true figure isn't known with accuracy. It takes a caloric surplus, spare protein and a considerable amount of time, though.
Dr McGuff says his own research indicates that recovery time is a continuum whose shortest period is about three days, and whose longest can be as high as twelve or fourteen, depending on genetics. In other words, in Dr McGuff's eyes, if you're training three or four times a week, you're trashing your recovery.
On average, then, Dr McGuff recommends training once every seven days or so.
The other key to effective training, says McGuff, is intensity. The signal, the imposed demand,has to be sufficiently intense that the body responds by construction of new tissue. That's hard: the body likes efficiency,and will usually expend as little energy as possible to achieve a task. It hates to build new tissue, because of the biological expense involved. So the stimulus has to be high. High enough to cause major discomfort, physical and emotional. Dr McGuff says his workouts should be "panic-inducing" and that they should extend past failure. When you can no longer move the weight,he says, "if you're appropriately instructed or appropriately motivated, you'll continue to try to move the weight for another then or twenty seconds."
Using machines is frowned on by many fitness professionals. They argue that using machines produces less training adaptation because there's no requirement for stabilization or patterning, and that the movement arc for many machines is wrong for the majority of people anyway. Better bodyweight, better barbells, better dumbbells, kettlebells, better sandbags, than machines, they argue. But their reasoning is actually the same as McGuff's, just inverted. He recommends machines because they don't require any thought for form. As a result, he says, "you can concentrate all your mental energy on putting forth effort, without thinking you're going to hurt yourself." He also recommends very slow movements, which is contentious: while it's supposed to produce more fatigue, high-threshold motor units, those with most potential for growth and strength, are best recruited at high speed.