Constrained action hypothesis, Venus, and the art of living

📝 Weekly paper summary

Investigating the Constrained Action Hypothesis: A Movement Coordination and Coordination Variability Approach (Vidal et al., 2018)

Category

Cross-over study

Context

Over the past ~20 years, there have been various works regarding the impact of different foci of attention on performance (e.g., see some previous newsletters, such as that from September 7th, 2021 and October 6th, 2021, for summaries on different topics regarding foci of attention).

Although various studies have supported that an external focus of attention improves performance outcomes and learning, the mechanisms responsible are less clear. The most commonly cited mechanism is the Constrained Action Hypothesis which suggests that an external focus promotes automaticity. In contrast, an internal focus of attention constrains the neuromuscular system and disrupts automaticity. In other words, an external focus of attention should "release" more degrees of freedom, whereas an internal focus of attention should "freeze" more degrees of freedom. This, hypothetically, should mean that the absolute coordination patterns and coordination variability should be different when performing a task with an internal versus an external focus of attention.

Therefore, the purpose of this study was to assess whether the intra-segment coordination and coordination variability (measured via vector coding) were different when performing a broad jump with an internal versus external focus of attention. The researchers hypothesized that the absolute coordination (i.e., the average coupling angle) would be different between the foci of attention. Furthermore, the researchers hypothesized that coordination variability (i.e., the coupling angle variability, computed using circular statistics) would be lower with an internal ("extend your knees as rapidly as possible") versus an external ("think about jumping as close to the orange cones as possible") focus of attention.

Correctness

This was a relatively simple study design, and the authors did a good job answering their intended question. Statistically, they verified they had more than adequate power to detect an effect size of 0.44.

However, there is one potential issue with their coordination variability measures. There was no way for the researchers to have known this at the time, but Stock et al. (2018) published data a few months later outlining that applying circular statistics can cause artifacts in the calculation of vector coding variability. Therefore, we can't fault the authors for their selected methods, but we should still keep this issue in mind when interpreting their coordination variability findings.

Contributions

• More data supports that focusing on movement effects versus movement processes result in increased jumping performance.
• Builds upon previous work by demonstrating that how people coordinate their hip, ankle, and knee joint is different for an external focus of attention is different relative to an internal focus of attention (there is data outlining differences in neuromuscular recruitment between the foci of attention, but less about differences in movement kinematics). Specifically, it supports the hypothesis that action is constrained with an internal focus of attention. The instruction to extend the knees rapidly while jumping resulted in coordination dynamics dominated by motion at the knee with relatively minimal motion at the ankle and hip. In contrast, the opposite was the case when instructed with an external focus of attention.
• Coordination variability was not different between the two foci of attention, which is a fairly surprising result. However, it highlights the importance of considering the type of tasks performed when assessing movement variability. Since jumping is a discrete task performed over relatively shorter durations (compared to gait, for example), environmental constraints don't regulate movement production as much. Thus there is less of a need to display coordination flexibility to accommodate fluctuations in the environment. Furthermore, because jumps are performed quickly, it's less likely that adjustments would be made "on the fly" as they may in dart-throwing (Lohse et al., 2010). In summary, the task type, duration, and velocity will influence whether instructions impact coordination variability. To put this in S&C terms, coordination variability is impacted by the interaction between 1) the exercise selected, 2) the demands imposed (i.e., loads, velocities, and time-under-tension/work), and 3) the foci of attention.

🧠 Fun fact of the week

The days on Venus are longer than the years. It takes about 243 earth days for Venus to rotate once (which is the slowest rotation in the Solar System), but only about 224 earth days to rotate around the sun.

🎙 Podcast recommendation

This podcast is somewhat "old" now, but I enjoyed Dr. Gray's breakdown of this paper. The Perception & Action podcast has quite a few other great episodes as well, and I highly recommend checking it out!

🗣 Quote of the week

"You have proof in the extent of your wanderings that you never found the art of living anywhere - not in logic, nor in wealth, fame, or in any indulgance. Nowhere. Where is it then? In doing what human nature demands. How is a person to do this? By having principles be the source of desire and action. What principles? Those to do with good and evil, indeed in the belief that there is no good for a human being except what creates justice, self-control, courage and freedom, and nothing evil except what destroys these things."

- Marcus Aurelius, Meditations, 8.1(5)