New research suggests that doing biceps weight training with just the right arm stimulates both limbs. Even if the other arm doesn't do a single push-up.

Researchers from institutions in Chile, France and Australia conducted this recent study. Thus, one immobilized arm holds its muscle mass and can even gain strength if the other arm trains resistance for a month. Especially, if the exercises are of an "eccentric" nature.

However, bodybuilders already know that muscles work together to generate movement, so muscles support the skeleton as you lift iron.

So it's no surprise that 'resting' body parts are actually going into action as well.

One arm stimulates the other

Anyway, little research has been done to test this possibility in weight training on the opposite limbs such as the arms. The two previous studies that measured the effect did not consider the nature of the exercise.

However, the type of weight training performed is a determining factor. When a dumbbell is lifted to the shoulder with elbow flexion, this movement is caused by a concentric contraction of the biceps. In other words, the fibers contract and the muscle shortens.

Image: Pixabay

The eccentric contraction, on the other hand, controls arm extension. That is, the biceps fibers are still under the effect of the loaded weight, but collectively the whole muscle lengthens.

Both exercises have their place in developing fitness, but if strength is the goal, focusing on eccentric contractions may be the way to go.

The test to analyze if eccentric contractions are preferable in the immobilized arm was carried out with 18 men and 12 women, with ages between 18 and 34 years old. Then, the researchers invited them to spend one month with a sling on one arm for eight hours of their day (excluding driving, showering and sleeping).

A third of the group just lived as if with a broken arm. The rest split in two: one group did concentric and eccentric exercises three times a week and the other ten stayed only in eccentric routines.

How the study was done

In conclusion, at the end of the month, the entire group had their biceps that was immobilized studied. The metrics used were circumference, strength, and neural input.

Participants who performed the eccentric exercises increased the strength of both arms, so it has a very powerful cross-transfer effect, said medical researcher and one of the study's authors, Ken Kazunori Nosaka.

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Incidentally, this group also had 2% muscle loss in their immobilized arm, compared to those who did not exercise and had a 28% muscle loss.

So, those who have not done any exercise, need to regain the strength of the muscles again. It was just not clear whether the exercises help the immobile limb to avoid atrophy of the muscles.

Anyway, one possibility is that the brain also sends signals to the other side of the body when controlling a complex set of muscle contractions in a limb.

The scientific study was published in the journal Scandinavian Journal of Medicine & Science in Sports .