Defining Coordination, Sharks, and Time-Restricted Eating

📝 Weekly paper summary

Clarifying the Biomechanical Concept of Coordination Through Comparison with Coordination in Motor Control (Kimura et al., 2021)

Category

Review

Context

Although it can be somewhat boring and pedantic, it's essential to ensure that terminology between fields remains consistent to minimize miscommunication and maximize overall knowledge production and dissemination.

This paper highlights that various biomechanics and motor control researchers have defined "coordination" differently. Furthermore, within the field of motor control, the computational versus ecological theories define coordination differently. Given the lack of consistency in the definition of coordination in biomechanics studies, the emphasis of this paper was to review the meaning of coordination used in the biomechanics and motor control literature to establish a biomechanical perspective on coordination.

Correctness

Overall, the paper provides an excellent review of the various theories and computation techniques in research papers where "coordination" is emphasized. There was really only one claim, though, that jumped out to me that I thought may have been slightly misleading. On pages 5-6, the authors of the current paper write:

"Latash and colleagues described synergy as not related to a reduction of the amount of computation in the CNS. According to this view, it is assumed that the CNS does not produce a single optimal solution but provides families of combinations between elements that can achieve the motor task with acceptable accuracy. If the CNS determines a single solution from an infinite number of possibilities, an enormous amount of computation is required. Therefore, it is natural to assume that CNS will reduce the amount of computation. However, if the CNS provides a family of combinations that can achieve the motor task, the amount of computation required would be reduced. Therefore, there will be no need to eliminate the extra degrees of freedom."

The main idea to emphasize in this passage is Latash's proposed emphasis on a computational theory of motor control regarding how the organism can simplify the computations required of the CNS. However, I don't believe this is an accurate representation of Latash's ideas. For example, consider his 2018 paper Abundant Degrees of Freedom Are Not a Problem, where he writes on page 4:

" The alternative approach views the CNS as a physical (physiological) system that performs no computational operations but behaves according to laws of nature. Of course, researchers express and analyze such behaviors with computational means (e.g., equations). However, it is never assumed that objects of study perform such computations. This would be equivalent to assuming that the Sun measures the masses and distances to planets (and other celestial objects) and then computes forces that have to be applied to those planets to ensure their regular motion. This is unacceptable in physics. Hence, if one wants to understand laws of nature that define movements, one has to start with formulating the problems adequately and searching for such laws.

Also, consider his 2012 paper titled The Bliss of Motor Abundance (page 3):

"Consider the following problem: When an action potential is generated on the membrane of a neuron, a huge number of Na+ ions cross the membrane. There are many more ions in the vicinity of the site where the action potential is being generated. How does the CNS decide which ions should cross the membrane? This is a problem with zillions of unknowns. Likely, 100% of the readers would agree that the CNS does not micromanage at such a level. It does not care which particular ions participate in the process. The laws of physics make sure that about the right number of ions cross the membrane... Consider now the aforementioned problem of defining a motor unit recruitment pattern for a desired level of muscle activation. Does the CNS care about specific patterns of recruitment or does it allow laws of physics – including the size principle (Henneman et al. 1965) – solve the problem? In this context, “physics” implies classical physics, chemistry, and physiology; however, it does not imply computation."

Therefore, I'm not sure the authors of this paper have represented the ideas proposed by Latash as accurately as possible by categorizing his ideas under the "computational" perspective. Perhaps a better delineation for the subheadings in this paper (Computational perspective versus Ecological Perspective) could have been outlining how much each theory emphasizes the CNS (i.e., a strong versus weak emphasis on the CNS). I might be misinterpreting the authors' intentions, though, and I should highlight again that the paper itself is still quite informative.

Contributions

• Biomechanics Perspective of Coordination = relations between segments that act toward meeting a functional requirement (i.e., task goal)
• The Computational Perspective of Coordination = neural organizations that act to achieve a task goal while simultaneously reducing the number of degrees of freedom to solve the computational problem on the CNS
• The Ecological Perspective of Coordination = system elements self-organize (without input from a "controller," such as the CNS) to achieve a task goal and reduce the degrees of freedom.
• Irrespective of the theoretical basis (which should also be clarified), coordination should be defined relative to a task goal.
• A criticism of some of the research and techniques of those using an ecological perspective to study coordination is that self-organization of system elements does not imply that the elements act toward achieving a motor task. For example, an argument presented by the authors is that computing the relative phase, especially to look for phase transitions in finger oscillations, means that the purpose of the task is not necessarily achieved. More generally, some methods of quantifying coordination are purely descriptive as there is no "goal" that we are quantifying segments working towards. Although this would appear to question why researchers compute measures such as relative phase or cross-correlations, I think it's important to consider what Hamill et al. (2012) write (pages 2-3): "In gait dynamics, the goal-directed end-point is not a discrete spatial location, but the maintenance of segmental relations over many cycles that define the locomotor pattern itself." Therefore, the "goal" may not be as simple as a single end-point in space and time and may instead encompass segmental relations across time. Regardless, what "coordination" encompasses in a study is crucial for selecting a measurement technique to capture the proposed construct.

🧠 Fun fact of the week

This is one of those fun facts that kind of makes sense when you think about it after, but still, it blows my mind. Species of sharks have been around for about 400 million years. Trees, on the other hand? Only 350 million. That means that sharks have been on earth for longer than trees!

When I think about it, this shouldn't be totally surprising since life started in the ocean. Still, though, I'd certainly chalk this one up as a fun fact!

🎙 Podcast to check out

I loved this episode. It's an interesting addition to some of the ideas discussed in Peter Attia's discussion on caloric restriction with Steve Austad that I highlighted in a previous newsletter. I've definitely been learning a lot about fasting and caloric restriction on general health during these podcasts!

🗣 Quote of the week

"Life is a journey, and if you fall in love with the journey, you will be in love forever."

- Peter Hagerty