Half hour of moderately intensive cardio training boosts interleukin-15 release

Interleukin-15, a muscle-building signal protein manufactured by muscle cells, is also released during and after cardio exercise. Japanese researchers found an increased concentration of interleukin-15 in men who had cycled at moderate speed for 30 minutes. Their study will be published soon in Endocrine Journal.

Interleukin-15 [the protein is shown here attached to its receptor] complements the effect of IGF-1. It's a growth factor for adult muscle cells. IGF-1 on the other hand stimulates the development of the stem cells of satellite cells into adult muscle cells. There are unconfirmed rumours doing the rounds that interleukin-15 is used as a doping substance.

Interleukin-15 stimulates the natural resistance of the immune system. This is the 'non-learning' part of the immune system that springs into action immediately when pathogens enter the body. In addition interleukin-15 inhibits the growth of fat tissue. In cell studies fat cells release their contents into the blood when they come into contact with interleukin-15.

It would seem to go without saying that interleukin is released during exertion, but researchers have not yet found any indication that confirms this theory in endurance athletes. The Japanese got 13 young men to run fast on a treadmill for half an hour at 70 percent of their maximal heartbeat.

The researchers monitored the concentration of interleukin-15 in the blood of their test subjects. They discovered that the concentration of interleukin quickly reaches a peak, but also recedes again quickly. An hour after the exertion, the rise in the level was no longer significant. And after three hours the difference had completely disappeared.