Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


1-finger exercise reveals unexpected limits to dexterity

Even seemingly simple movements seem to push the hand's neuromuscular control system to its limits, with implications for both human rehabilitation and robot hands

"Push your finger as hard as you can against the surface. Now as hard as you can but move it slowly - follow the ticking clock. Now faster. Now faster."

These were the commands for volunteers in a simple experiment that casts doubt on old ideas about mechanisms to control hand muscles. Complete understanding of the result may help explain why manual dexterity is so vulnerable to aging and disease, and even help design more versatile robotic graspers.

A research team led by Francisco Valero-Cuevas of the University of Southern California reports the paradoxical result in the Journal of Neuroscience.

"We expected to find," says the report, "that maximal voluntary downward force would scale with movement speed…. Surprisingly, maximal force was independent of movement speed."

The observation challenges theories that date back nearly seventy years about how the properties of muscles influence their everyday function, and how "redundant" our bodies are.

According to Valero-Cuevas, who holds a joint appointment in the USC Viterbi School of Engineering's department of biomedical engineering and the USC Division of Biokinesiology and Physical Therapy, in many tasks muscle force is affected by physiological "force-velocity" properties that weaken muscles as they move faster.

"That is why your bicycle has gears, and why as a child you could not speed up much on level ground," he explains.

Valero-Cuevas and his collaborators set up a simple experiment to characterize how finger velocity made a difference in the force produced during the common manipulation task similar to rubbing a surface, using a computer track pad or iphone. Adult volunteers wearing a closefitting Teflon cover on their forefingers applied fingertip pressure on a slippery Teflon surface linked to a force-measuring sensor.

First, the volunteers simply pressed as hard as they could without moving. Then, still pressing as hard as they could they moved their fingers against the surface to the beat of a metronome.

"As expected, maximal downward force diminished when motion was added to the task," the researchers wrote. "But remarkably, there were no significant differences … between slow, and fast movement speeds… even though the movement speeds varied 36-fold."

The paper, "Maximal Voluntary Fingertip Force Production is Not Limited by Movement Speed in Combined Motion and Force Tasks," goes on to discuss and rule out several possible explanations for the result, including differing levels of dexterity by the subjects, non-linear responses by muscles, and finger-muscle asymmetries.

The explanation proposed by Valero-Cuevas and collaborators (and former students) Kevin G. Keenan of the University of Wisconsin/Milwaukee, Veronica J. Santos of Arizona State University, and Madhusudhan Venkadesan of Harvard University, is that the universe of possible commands sent by the brain to the muscles is severely limited by the mechanical nature of the task, even for ordinary manipulation tasks.

That is, say the scientists, that even for seemingly-simple real-world tasks where we must control both force and motion, the neuromuscular system can be pushed to its limits of performance.

This complements other recent work by Valero-Cuevas showing how other ordinary tasks like tapping a surface are extremely challenging to the nervous system.

Together these results begin to identify the mechanical pressures that could have driven the evolutionary specializations of our brains and bodies that make our hands so dexterous.

"These apparently esoteric results have tremendous implications for both humans and robots," Valero-Cuevas says. "For one, they bring together basic research and clinical reality by helping explain the high vulnerability of dexterous everyday function to disease and injury in spite of the many muscles and joints we have.

"In addition, they suggest to engineers that adding redundant motors to robots may actually be the key to making them dexterous."

The detailed interactions among muscles and body mechanics are complex and defy easy mathematical modeling at this time, he adds, but further study may offer clues.

The research was supported in part by grants from the NSF and NIH.

Eric Mankin | EurekAlert!
Further information:

More articles from Health and Medicine:

nachricht NIH scientists describe potential antibody treatment for multidrug-resistant K. pneumoniae
14.03.2018 | NIH/National Institute of Allergy and Infectious Diseases

nachricht Researchers identify key step in viral replication
13.03.2018 | University of Pittsburgh Schools of the Health Sciences

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

Im Focus: Radar for navigation support from autonomous flying drones

At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.

Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

International Virtual Reality Conference “IEEE VR 2018” comes to Reutlingen, Germany

08.03.2018 | Event News

Latest News

Wandering greenhouse gas

16.03.2018 | Earth Sciences

'Frequency combs' ID chemicals within the mid-infrared spectral region

16.03.2018 | Physics and Astronomy

Biologists unravel another mystery of what makes DNA go 'loopy'

16.03.2018 | Life Sciences

Science & Research
Overview of more VideoLinks >>>