Nav: Home

What makes a reach movement effortful?

June 06, 2017

When choosing between alternative actions, we have to compare the positive outcomes of those actions and weigh them against their costs. Whether a predator hunting prey, a monkey picking fruits, or a human wavering between stairs and elevator, the physical effort associated with executing an action is a relevant cost and hence a decision factor. Understanding how we estimate movement effort is thus necessary to understand how we take decisions.

To study physical effort, human subjects were asked to repeatedly choose between arm movements which differed in amplitude or duration and in force. Not surprisingly, effort increased with the strength of a force resisting the movement. The researchers managed to quantify this dependency precisely, showing that effort was proportional to the square of that strength. Additionally, effort was higher when the movements involved weaker muscles, even for movements that necessitated only little strength. More surprisingly, Morel and colleagues showed that the distance covered by the movements did not determine effort. Instead, effort depended on the duration of the movements, with movements that lasted longer feeling more strenuous than brief movements.

"Our results allow us to estimate action-related costs in decision-making, showing they cannot easily be predicted from energetic expense", says Morel. "More than that, the results also give weight to the idea that action selection in decision-making and in movement execution have common properties and hence might be based on shared mechanisms." When a given action is executed, its goal can typically be achieved in many ways. For example, the multiple joints of the arm provide a large flexibility in how we could conduct reaches to a given target object. Nevertheless, when repeating reaches towards the same target, we tend to execute them in the same optimized way. "We conclude that previously described optimization principles during movement execution seem to also serve as guiding principles during economically motivated conscious choice before movement execution", says Alexander Gail, head of the research group. Understanding how we estimate movement effort is an important step towards understanding how we take decisions.
-end-
Original publication

Morel P, Ulbrich P, Gail A (2017) What makes a reach movement effortful? Physical effort discounting supports common minimization principles in decision making and motor control. PLoS Biol 15(6): e2001323. https://doi.org/10.1371/journal.pbio.2001323

Deutsches Primatenzentrum (DPZ)/German Primate Center

Related Force Articles:

A new force for optical tweezers awakens
When studying biological cells using optical tweezers, one main issue is the damage caused to the cell by the tool.
Converting biomass by applying mechanical force
German nanoscientists have succeeded in demonstrating a new reaction mechanism to cleave cellulose efficiently.
Elucidating cellular responses to force
Accumulated evidence suggests that physical force plays an important role in various developmental processes of fertilized animal eggs.
Self-growing materials that strengthen in response to force
A strategy inspired by the process responsible for muscle growth could lead to the development of stronger, longer-lasting materials.
Seeing and avoiding the 'blind spot' in atomic force measurements
Researchers have discovered a 'blind spot' in atomic force microscopy -- a powerful tool capable of measuring the force between two atoms, imaging the structure of individual cells and the motion of biomolecules.
More Force News and Force Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...