What would happen if you train just one arm?

Let's say that you are going to start training for an arm wrestle tournament coming next month. Knowing that you are only going to use your right arm and there's only limited time left, you decided to train just your right arm. What would happen to your left arm by the end of the training?

 a. your left arm would get weaker, and you would end up looking like this pic (  ..)

 b. your left arm's strength would be the same as before

 c. your left arm would get stronger as well

 d. your left arm would be jealous and leave you.

The answer is,,,,,, C!! Can you believe that?

how on earth does that happen?? 

Well, the secret lies in a principle called "cross education".  let me explain this.

What is cross education?  Cross education is a neurophysiological phenomenon where an increase is strength is witnessed within an untrained limb following unilateral strength training in the opposite, contralateral limb. A recent review of the literature has shown that strength in the untrained limb may increase up to 22%, and averages about 8 %. 1.

How does it work? although the exact mechanisms of cross education is not yet known, we know it has to do with "neural adaptation" since the increase in strength in the untrained limb is accompanied by greater Electromyography (it's a common research tool used to examine the magnitude of neural activation following training).

Ha! wasn't it interesting? I'll talk more about neural adaptation next time! so Buckle up!!

Reference  : 

1. Munn, J., Herbert, R.D., & Gandevia, S.C. (2003). Contralateral effects of resistance training: a meta-analysis. Journal of Applied Physiology, 96,1861-1866. doi: 10.1152/japplphysiol.00541.2003.