



Many people take out membership of a fitness club or gym but never set foot inside. This type of behavior, which the researchers termed the "physical activity paradox", has been demonstrated by earlier studies that contrasted the controlled system based on reason - I have to play sport to be healthy - with the automatic system based on affect - the discomfort and fatigue experienced during physical activity. When there is conflict between reason and affect, the physical activity behavior is not implemented, and the individual tends to remain sedentary. But what happens at the neuronal level?


Less time but more resources

"We made participants play the "manikin task" which involved steering a dummy towards images representing a physical activity, and subsequently moving it away from images portraying sedentary behavior. They were then asked to perform the reverse action," explains Boris Cheval. The researchers compared the differences in the time taken to approach the sedentary image and to avoid it. "We found that participants took 32 milliseconds less to move away from the sedentary image, which is considerable for a task like this," continues Boris Cheval. It was an outcome that went against the theory and the physical activity paradox. So, how can it be explained?


"On the other hand," points out Boris Cheval, "we observed that the electrical activity associated with two brain zones in particular, the fronto-medial cortex and the fronto-central cortex, was much higher when the participant had to choose the sedentary option." These two areas represent the struggle that takes place between reason and the affects, and the capacity to inhibit natural tendencies, respectively. "This means the brain has to use much more resources to move away from sedentary behavior, rather than follow its natural penchant for minimizing effort."

Fighting the legacy of evolution

Where does this inclination for sedentary behavior come from? "Making as little effort as possible was crucial for the human species during evolution", says the researcher. "This orientation towards saving and conserving resources increased the chances of survival and reproduction." Today, however, our modern society renders this energy optimization obsolete. "On the contrary, physical activity should be encouraged instead of putting temptations in the way to do less, such as escalators or elevators. For instance, we could modify the way public spaces are designed to reduce the opportunities for individuals to engage spontaneously in behavior associated with minimizing effort."


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