Unexpected limit of ingenuity

'Press your finger hard on the surface. Now press as hard as you can but move your finger slowly with the ticking of the clock. Time moves faster. Faster '.

Those are the commands for volunteers in a simple experiment. The experiment rejected previous ideas about hand control mechanisms. A complete understanding of the results can help explain why dexterity diminishes with age and disease, and even helps design more flexible robotic arms.

The research team is led by Francisco Valero-Cuevas of the University of Southern California reporting on this' paradoxical 'result in the Journal of Neuroscience, ' We have expected that the active force will be down to a maximum of billions. with speed of movement . Amazingly, maximum force is completely independent of movement speed '.

This observation challenges theories 70 years ago about the effects of muscle properties on its daily function , and the 'excess' of our bodies.

According to Valero-Cuevas, who currently works in the biomedical engineering department of the Viterbi USC School of Engineering and the Unit of Physical and Biological Therapy, in many muscular forces affected by physiological properties 'force' -speed 'weakens muscles when they move faster.

He explained: 'That's why your bike has a number, and why you can't accelerate quickly on the ground when you're young'.

Valero-Cuevas and his collaborators performed a simple experiment to describe how the speed of a finger changes the force produced in a normal movement similar to rubbing a surface, using a computer tracking pad. Volunteers wearing a close-fitting Teflon bag on the index finger pressed the tip of the finger down to a smooth Teflon surface connected to a force-measuring sensor.

First, volunteers simply pressed as hard as they could without moving their fingers. Then, while still pressing their fingers as hard as they could, they moved their fingers on the surface according to a metronome.

The researchers wrote: 'As expected, the maximum downward force decreases when motion is added. However, it is surprising that there is no significant difference between fast and slow motion, even when the movement speed is 36 times different '.

Volunteers wear a close-fitting Teflon bag with the index finger and press the tip of a finger on a smooth Teflon surface connected to a force-measuring sensor . (Photo: University of Southern California)

The article 'The maximum active force of the fingertips is not limited by the speed of movement in the combined force and motion experiment' has attracted many arguments and removed some possible explanations for the results, including differences in skill levels, nonlinear response of muscles, and asymmetry of finger muscles.

Explained that Valero-Cuevas and collaborators Kevin G. Keenan of the University of Wisconsin / Milwaukee, Veronica J. Santos of Arizona State University, and Madhusudhan Venkadesan of Harvard University, proposed the system of orders that the brain sent to muscle is limited by the mechanical nature of the experiment, including normal motor experiments.

This means that even for very simple movements that we have to control both force and movement, the motor neuron system can be pushed to its limits.

This result complements the recent studies of Valero-Cuevas, which shows that normal activities such as tapping on a surface can be a major challenge to the nervous system.

These results are the first step in identifying mechanical pressure that can lead to the specialized evolution of the brain and body, making our hands clever.

Valero-Cuevas said: 'These results are very important for humans and robots. First, they combine basic and practical medical research by explaining why the ingenuity is so vulnerable to age and disease despite the many muscles and joints we have. '

'In addition, they show that adding extra engines to robots can be the key to making them more clever.'

The specific interaction between muscles and body structures is complex and exceeds the mathematical models at the present time, but more extensive and in-depth research may provide necessary clues.

Research funded by NSF and NIH.