Normally you’ll probably perform a symmetric exercise program at the gym. In other words; you perform the same exercises with the left side of your body, as with the right side of your body. But what if you’re injured? What will happen when you’re only able to train one side of your body? Cross Education Training might just give the answer!

The theory leading to those questions is fairly simple. A lot of people might expect that muscle performance is mainly determined by muscle architecture (“the bigger the muscle, the stronger and better”). However, there is another major component, which is often overlooked: the neural component. Wondering why your gains aren’t visible after a few workouts? Same thing! Often, the neural component is improved before the physical component of the muscle itself. Don’t give up, those will follow soon!



Cross Education Training

So, when physically training one side of the body, you train the muscle, as well as the neural component. Since this neural component is important for both body sides, you actually might (partly) train both body sides with a single-sided (cross) exercise program!

“When physically training one side of the body, you train the muscle, as well as the neural component.”



To determine the extent of cross education training, Hedayatpour et al. studied the effect of a single-sided resistance training on muscular endurance* of the leg stretchers (quadriceps). It’s known that strength training can improve this muscular endurance, but what are the effects in a cross education training set-up?



Single-sided training, double effect

Just as hypothesized, time to exhaustion increased in both legs after a one-sided resistance training program. This increase was, not unsurprisingly, larger for the trained leg (improvement of +/- 28%), compared to the non-trained leg. But still, the untrained leg showed an improvement of +/- 19% in time to exhaustion. These increases in muscle endurance were accompanied by increases in muscle (electrical) activation (EMG-amplitude). This may be related to an increased neural drive to activate more muscle fibres to produce/ sustain the desirable force.

“Single-sided resistance training increases muscle strength and neural activity of the untrained muscle.”



These results confirm the results and suggestions of previous research, which showed that single-sided resistance training increases muscle strength and neural activity of the untrained muscle. Therefore, the strength gains seem to be mainly attributable to central neural adaptations. Another, alternative explanation might be that there is some sort of crosstalk between the right and left hemispheres of the brain, resulting in double-sided improvements after a cross education training.



Conclusion

Despite the fact that the untrained muscle gains are smaller than those of the trained muscle, the implications of the results might be huge. Especially for rehabilitation, cross education training might be useful for recovery and training of an affected limb!

More strength training tips? Try reading our other blogs as well!

* Ability of a muscle to sustain a continuous contraction over a longer period.

Hedayatpour N, Golestani A, Izanloo Z, Meghdadi M. Unilateral leg resistance training improves time to task failure of the contralateral untrained leg. Acta Gymnica. 2017;47(2):72-7.