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Restricted muscles grow faster

If you do strength training with light weights, lots of reps and the blood supply to your muscles cut off, you are likely to gain just as much muscle bulk as you would with regular strength training. Researchers at the University of Texas and the University of Tokyo reported this in an article that appeared two years ago in the Journal of Applied Physiology.

We already wrote about Kaatsu-training couple of weeks ago. In the study here, the test subjects trained their thigh muscles on an extension machine at 20 percent of their 1RM. They did thirty reps, waited thirty seconds and then did a set of fifteen reps. Then they did another two sets of fifteen reps, again with a wait of thirty seconds between.

In the experimental group [REFR] the blood flow to the leg muscles was almost totally cut off using a tourniquet. In the control group [CTRL] the blood supply was not restricted.

The researchers examined the blood and muscle tissue of the test subjects shortly after the training session to try and find out why Kaatsu-training has such an anabolic effect. You can obtain just as much growth from Kaatsu-training as from regular strength training with loads of seventy percent or more.

A possible mechanism is that the production of growth hormone increases by a factor of ten compared with the control group. A GH peak is normal in regular strength training, but if you work at 20 percent of the 1RM you don't see it.

Restricted muscles grow faster

The researchers measured more lactic acid in the Kaatsu group than in the control group. The concentration of free testosterone and IGF-1 in the blood did not change in response to the blood flow being restricted. The cortisol levels did rise by a significantly large amount in the experimental group.

Restricted muscles grow faster

The mTOR molecule is a key factor in muscle production and breakdown. When the muscle cells attach phosphorus groups to mTOR which is what happens during strength training or steroid hormone use the resulting phosphorylated mTOR activates other signalling molecules which induce the cells to produce muscle proteins. S6K1 is an important enzyme in strength training. The more phosphorus groups attached to the molecule six hours after a training session, the more muscle bulk athletes build up.

mTOR did not react to Kaatsu-training, but S6K1 did. The researchers don't understand how this happens. mTOR should activate S6K1, but it looks as though this didn't happen.

Restricted muscles grow faster

Whatever, the Kaatsu training did lead to increased protein manufacture compared with the control group training. See below.

Restricted muscles grow faster

The researchers don't think that the increased growth hormone production is a significant factor in the increased muscle tissue production. Instead, they suspect "that a greater number of normally inactive muscle fibers are recruited to lift a similar load when the blood flow is restricted".

J Appl Physiol. 2007 Sep;103(3):903-10.

Restricting blood flow makes muscles grow 14.02.2009