One of the first things I noticed when I arrived in Paris is the amount of traffic and the prevalence of people who use the Metro to get around. Even though I’ve lived in Atlanta my whole life, I think I had been on MARTA once when it was full to standing room only, and that was only because two big events ended around the same time. However, every morning on my commute to class in Paris it seems like we are fighting to be able to get a spot on the train. Another major difference that I’ve noticed between these train systems is that the Metro trains tend to have more turns in the tracks, which never fails to make a large group of the people standing momentarily lose their balance. Here are the maps so that you can compare the two.
Whenever the train goes around a bumpy turn, you always see people taking a step or people who weren’t previously holding onto anything reach out to the nearest pole. Considering the number of ways the train can throw you off balance, it’s almost surprising that people never fall over. This made me wonder, why is it that we are able to balance so easily even when the ground beneath us is moving?
According to Chiba et al. (2016), your body uses information like vision, the location of your body and limbs, touch, and the position of your head to maintain its balance. Together, these all allow the central nervous system to help control your posture and if one of the inputs becomes less reliable, then the body compensates for it by paying more attention to the other inputs. According to Takakusaki (2017), these inputs all enter the brain where they are processed in various regions. These signals can then follow either automatic or cognitive pathways in order to then exit the brain through the spinal cord so that the signal can be delivered to the body. The automatic pathway, which controls balance, is much more direct which allows you to respond faster.
Coelho et al (2016)’s study added an extra layer to understanding balance by giving people an extra task while testing their balance. They tested balance while an individual was holding a tray with a cylinder either standing on the flat side or lying on the round side balancing on it. This reminded me of when I’m on the metro trying to hold onto my bag, phone, wallet, etc. Because of the risk of pickpocketing, I try to keep everything in front of me and I keep my wallet and phone in my hand rather than putting my phone in my pocket or letting my wallet hang off my wrist. I see others on the Metro holding items in their hands all of the time as well. While the cylinder on a tray is definitely more complicated to keep balanced than a phone or bag, I felt like this extra aspect would help to see what is going on when people are staying steady on the Metro.
They placed a harness around the participants’ stomachs which applied a constant pressure pulling them backward. They then asked them to count down from a random number by threes while they were holding the tray. They then released the harness causing them to move forward. This would cause them to have to readjust so that they wouldn’t drop the cylinder. They also tested the participants using the same procedure except without making them count down.
Both counting down and the direction the cylinder was placed in affected how fast the tray moved, how fast their upper body moved, and how much their upper body moved. Additionally, counting down but not the direction of the cylinder affected how much their center of mass moved. These results show that when the cylinder was in a more unstable position, they were able to adjust so that it moves less. They also showed that having the cognitive task seemed to make them move more.
I found these results interesting because it means that having something unstable seems to make you balance more. This seemed a little counter-intuitive to me at first, but it makes sense that the amount of attention you are spending on balancing could impact how well you balance. This is evident in how the cognitive task appeared to make balance worse. I think it would be interesting to see if the people who are hold ing objects in their hands or the ones that are zoning out are the ones that stumble more on the Metro. I also think it would be interesting to see if repetition affects balance. For example, if the people who rode the metro everyday stumbled less on the turns than visitors from cities that don’t rely as heavily on a train system or if the harness being released would cause the participants to be better prepared for it.
Chiba, R., Takakusaki, K., Ota, J., Yozu, A., & Haga, N. (2016). Human upright posture control models based on multisensory inputs; in fast and slow dynamics. Neuroscience Research, 104, 96-104. doi:10.1016/j.neures.2015.12.002
Coelho, D. B., Bourlinova, C., & Teixeira, L. A. (2016). Higher order balance control: Distinct effects between cognitive task and manual steadiness constraint on automatic postural responses. Human Movement Science, 50, 62-72. doi:10.1016/j.humov.2016.10.008
Takakusaki K. (2017). Functional Neuroanatomy for Posture and Gait Control. Journal of movement disorders, 10(1), 1–17. doi:10.14802/jmd.16062