Low-intensity cardio stimulates muscle growth through strength training, high-intensity cardio does not
Frequent low-intensity cardio training accelerates muscle growth through strength training - and frequent high-intensity cardio does not. An animal study, that Japanese researchers at Nagoya University published in Physiological Research, suggests this.
The researchers experimented with 3 groups of male mice. For 4 weeks, the Japanese let one group run at a low speed for half an hour, 5 days a week, on a treadmill [LOW] for 4 weeks. A second group of mice had to run half an hour during this period with a good pace [HIGH], a third group of mice did nothing [REST].
After these 4 weeks, the researchers removed the gastrocnemius muscle in one of the mice's hind legs. As a result, other muscles, such as the plantaris and the soleus, had to take over the tasks of the gastrocnemius [Overloaded legs]. This intervention more or less imitates the effect of strength training.
In the other hind leg, the researchers did not remove any muscles [Sham operated legs].
Then the researchers waited a week, and looked what had happened to the muscles in the back legs of the mice.
In the overloaded legs, the researchers saw that the plantaris muscle had grown, and the soleus somewhat less. That is not so strange, because in the soleus are relatively more small slow muscle fibers than in the plantaris.
The largest increase in plantaris muscle had occurred in the mice that had done moderate-intensity cardio training.
In a way that the Japanese do not understand, moderately intensive cardio training before the overload phase causes an extra activation of anabolic signaling molecules such as AKT and mTOR.
"Our study showed that chronic low intensity aerobic training enhanced muscle growth, indicating that mild aerobic exercise plays a role in maintaining muscle mass", write the researchers. "Our data showed for the first time that chronic low-intensity aerobic exercise precipitates overload-induced muscle growth."
Physiol Res. 2018 Nov 23;67(5):765-75.
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