One-finger Exercise Reveals Unexpected Limits To Dexterity



ScienceDaily (July 12, 2009) — "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.

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http://www.sciencedaily.com/releases...0708073847.htm