Lifting Heavy Things With Our Brains

            When thinking about the act of lifting weights, I always wondered what exactly was happening to make me “stronger”. Is it just a mindless act to help increase the size and strength of your muscles? Or does the brain work just as hard as the muscles do?

I found an interesting study in the Journal of Applied Physiology that looked into the neural adaptations that occur during muscle training. I have highlighted the most interesting findings:

In Figure 3A we can see the comparison between the torque (a) and EMG (b) in the tibialis anterior during flexion of that muscle before and after training. We can see in part Aa of Figure 3 that the relative torque produced is pretty similar, but we can visualize the increased rate of development of that torque and an earlier and intensified activity of the EMG. In Figure 3B we have a representation of the same muscles and their motor units in relation to their action potentials(b,c). We can see the effect training has on the action potentials of the motor units with an increased rate of firing and more double discharges after training (interspike intervals < 5 ms). This points to a neural adaptation mechanism that allows for the muscles to fire more quickly and often after training. Although the mechanism of adaptation is still unknown, there is evidence of an increase in neural involvement as a result of strength training.

They also discussed the adaptation in the coactivation of muscles. Coactivation is the recruitment of agonist and antagonist muscles to increase joint stability during contraction of a muscle. They found that coactivation of the antagonist muscles reduce within the first week of training. They compared an athlete and someone who did not do weight training and observed an adjustment by the nervous system to reduce the coactivation of the antagonist muscle of that contraction leading to a larger net force in the athlete. 

Lastly, they found evidence to show divergent effects of skill and strength training on the nervous system by using data on motor unit synchronization. They found that there was the most motor unit synchronization in weight lifters and the least synchronization in skilled musicians. 

All in all, their findings lead me to believe that your brain is working just as hard as your muscles to adapt during training.

Duchateau, Jacques, et al. “Training Adaptations in the Behavior of Human Motor Units.” Journal of Applied Physiology, vol. 101, no. 6, 2006, pp. 1766–1775., https://doi.org/10.1152/japplphysiol.00543.2006.