The year was 1894. The first college basketball game was won by the University of Chicago over Chicago YMCA 19-11. The 1st Stanley Cup was captured by Montreal over Ottawa, 3-1. Bobby Lowe became the first player to hit 4 home runs in 1 ball game. Under the vision of Baron Pierre de Coubertin, the International Olympic Committee was founded at the Sorbonne, Paris. In New York City, the United States Golf Association formed. Coca-Cola was sold in bottles for the first time. In Scotland, Patrick Manson suggested that mosquitos spread malaria.

And in 1894 at the Yale Psychology Laboratory, Edward Wheeler Scripture (1864-1945) publishes a small paper “On the education of muscular control and power”. This paper will be but a drop in the bucket of a very prodigious research output spanning Scripture’s career. But the reverberations from that drop will ripple until present day.

Scripture did a very interesting thing. Or many interesting things, of course, but one in particular that is relevant to our story here. Scripture took old observations from 2 different branches of science and sought to apply the principles to his own work. And he did so with a study based on observations from only 2 people.

Scripture looked back on two studies published many years earlier by German scientists. Gustav Fechner (1801-1887)  published a paper in 1857 that was one of the first studies to actually document how practice could increase strength. Fechner lifted 2 dumbbells (~9 lbs) in each hand up over his head as many times as he could every day for 60 days. His first day was 104 repetitions and he reached 692 on day 55.

Alfred Whilhelm Volkmann (1801-1877) had an interest in whether you could get better at detecting touch if you practiced trying to get better at it. He did a number of experiments but the paper he published in 1858 presented data showing that if you trained over several weeks using the left fingertip you would get better at detecting things with that fingertip. That all seems pretty obvious. So far I’ve told your Fechner got stronger when he kept lifting weights and Volkmann showed you got better touch sensitivity of you practiced touching things!

But Volkmann also did something else. Something that Scripture found fascinating. Volkmann found that the sensitivity of the other fingertip—the right one in this case—also showed increased sensitivity. That’s despite not using the right fingertip for training!

Touch sensitivity gained by training, then, could transfer to the same part of the body on the other side. Scripture then had the clever idea of combining the strength training concept of Fechner and the sensitivity transfer that Volkmann had written about.

In his study, Scripture’s two participants were actually co-authors. One (this was Miss Brown—an endearing part of this paper is how he just writes out the names of the participants, giving the text a Dr. Seuss-like quality) did strength training (“muscular power”) by squeezing a rubber bulb (like that on the end of a blood pressure cuff). The other (Miss Smith) did skill training (“muscular control”) by trying to put a needle through an electrified drill board with holes of decreasing diameter. If she touched the metal on the board instead of going through the hole, the trial ended. It was basically a bit like playing the Hasbro game “Operation”. But by candlelight.

Both participants did initial tests to see how strong (Miss Brown) or how accurate and steady (Miss Smith) they were with both hands. Then they did training in squeezing the bulb (9 days) or putting the needle through as many holes as possible (10 days).

Not that surprisingly Miss Brown got stronger (~70%) on the side she trained and Miss Smith got more accurate (~45%) with her trained hand. Clearly you get more skilled and stronger with practice. Not so surprising and even if no one had done an official “study” of it, this isn’t something that would really shock anyone. The bit that shocks comes next.

But understand why it may be so shocking requires one more little bit of background. It is widely known now in popular culture that there is a certain lateralization of function in the brain. For example, going back to the pioneering work of French scientist Pierre Paul Broca (1824-1880), it was known that articulation during speech is greatly impaired when there is damage to the left frontal cortex—now known as Broca’s area.

In motor systems the lateralization concept can be seen in the idea that one hemisphere activates—via the spinal cord—muscles on the opposite side of the body. Canadian neurosurgeon Wilder Penfield (1891-1976) was prominent in epilepsy surgeries and showed in the 1940s that certain brain regions concerned with motor actions were very lateralized. As part of pre-surgical mapping of the brain, different areas were electrically stimulated and then the muscles responded with twitches.

This was pretty good evidence that there was a strong organization of left hemisphere controls right, and right hemisphere controls left side. At least for the last output from the motor systems of the brain before commands descend the spinal cord. Of course, like many observations in science, the true nature of this organization is still being sorted out and the picture is not nearly as clean and clear as thought. (More later!)

Because of all of this, I think it is a reasonable conclusion that training the muscles on one side of the body should really affect that side and maybe not so much the other side. Which, of course, was at the very heart of the matter that Scripture was trying to investigate. Is there an education of the crossed side of the body when one side is trained? In modern terms we would ask, “are there neuroplastic changes that allow the transfer of skill from one side of the brain to the other?”

And the answer lies in what happened in the other, untrained arm and hand of Miss Brown and Miss Smith. Even though she didn’t train that other side, Miss Brown got ~40% stronger! And, Miss Smith showed an increase in accuracy just over 25% with her untrained hand. Or maybe we shouldn’t call that other side untrained, because clearly it was trained. But not trained directly by physical practice. Instead, some neuroplastic adaptations had to have occurred.

Scripture’s short paper in 1894 showed that training on one side of the body could affect strength and skill on the other side of the body for the same muscles and actions. It’s also interesting that the difference across the body was about 50%. That is, you get about half the increase in the untrained limb that you would get from doing the training.

Since those days in 1894, there have been many studies on the cross-education effect in the context of neuroplasticity—the adaptive changes that the brain produces as it adjusts to new demands. These studies have revealed that this effect can be seen in many different muscles and actions across the body. Research has shown that the effect itself seems to involve a complex interaction of changes in different regions of the brain and spinal cord.

An interlude…there’s an interesting application here to skill learning generally, and which resonate with my own experiences in martial arts. We learn many different training combinations and patterns of movement sequences, for example in fighting drills and in the “forms”, patterns or kata used for training. Usually we learn these and practice to a certain degree of skill by using a coordination sequence that may emphasis one side of the body more than the other. The idea is that these will eventually be practiced on both sides and indeed they seem to transfer well from side to side. In my own experience this works much better if you first develop a reasonable skill level on one side before trying to learn complex patterns on the other side.

Many details—particularly about the exact mechanism and specific brain regions involved—still remain to be worked out. But there are many take-away messages from Scriptures work. A key one is the synthetic approach of taking observations from very different studies and combining them in a powerful new idea. Another is a clear documentation of the manifold ability the nervous system has to adapt itself to changing demands.

An overarching point is that response to physical training for strength and skill initially comes from the nervous system. So your initial trips to the gym that made you stronger that first month? It’s all in your head. In the motor areas of your brain, to be exact.

Despite all this, in my own mind the question has always remained—what is the real application of this cross education phenomenon? I am pretty big on functional interpretations and applications. So, what is the functional importance of training one side of the body and getting half (the actual range is large) the strength gain on the other side? Obviously if you really want to get stronger with both sides you should train both sides, right?

The asymmetry of this “cross education” phenomenon has always struck me as kind of bizarre and of uncertain relevance. As a neuroscientist I have come across many observations that go in the file of “epiphenoma”—minor side effects of something else. I used to file cross education in that category.

And so I didn’t pay it a lot of attention. Until recently, that is. I am now paying a whole lot more attention to cross education. That’s because a little while ago I started thinking more about times when an asymmetry already exists in the body. Like after a stroke. And I paid more attention to the work of colleagues who asked questions about what would happen when one limb is in a cast? How useful could this assymetrical “cross education” of strength and skill be when asymmetries like these already exists? And is need of an equalization. What about then?

Well, that is the topic of my next post. Please stay tuned!

© E. Paul Zehr, 2013

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