Let’s go back to classic blood flow restriction training for a minute. A band or tourniquet slows the movement of blood flowing back to the heart. This allows the blood to “back up” in the extremities, that is, fill them with blood.
This “feedback” blood increases the concentration of lactate in the occluded area, which tricks the brain into thinking that the muscles are working much harder than they really are. In turn, the pituitary supposedly releases additional amounts of growth hormone (GH), IGF-1, mTOR, and myostatin, all of which play important roles in muscle growth.
Much the same thing happens during partial reps. In effect, the training style “kinks the hose” and blood is occluded in the working muscle.
However, Goto and colleagues argue that “hypoxic muscle stimulation” (growth stimulation through low blood oxygen levels) is also important during conventional training, since it occurs, to some extent, even when you’re doing full range reps.
However, the more advanced your training, the larger the diameters of your arteries (up to a point). This results in blood flowing freely, too freely, through those big garden hose arteries. As a result, there is no hint of occlusion and a diminished growth response is obtained.
This also does not seem to be pure conjecture. One of his earlier studies found that 8 weeks of training resulted in just that: an increase in artery diameter and blood flow, leading to “blunted hypoxic muscle stimulation.”
Not only that, but there is the simple physics of conventional training that arguably attenuates the growth response: Every time your limb reaches 180-degree extension (when your arm is straight out from your body), you “uncoil” the hoses and allows the arteries and capillaries to decompress, thus allowing blood to flow freely (without occlusion). No occlusion, no GH, IGF-1, etc.
Hence the beauty of partial reps: constant muscle contractions, resulting in high occlusion, leading to greater mechanical and metabolic stress (than full-range-of-motion reps), and subsequently more growth.
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