Scopolamine increases prehensile force during object manipulation by reducing palmar sweating and decreasing skin friction

Abstract

The aim of this study was to determine whether relatively long-term changes in skin friction induced by a pharmacological blockade of sweat excretion would alter the grip forces applied to objects of a variety of different surface textures and frictions. Five men and three women were asked to lift the vertically mounted armature of a linear motor between the thumb and index finger and to hold it against an opposing force for 2 s. A 1.0-kHz tone indicated to the subject that the manipulandum had been correctly positioned between the upper and lower position limits. The linear motor generated a 2.5-N force tangential to the skin surface simulating an object weighing approximately 250 g. Three different polyamide plastic surfaces (either smooth or etched with 1.0 mm high Braille beads evenly spaced at 2- or 3-mm intervals) contacted the fingers in these experiments. Subjects lifted and held in a precision grip one of the three surfaces for blocks of ten consecutive trials, but the order of presentation of the three different textures was varied to offset the effect of expectancy. On a second block of ten trials the subjects were requested to release the object slowly to measure the ratio of the grip force normal to the grasped surface to the tangential load force at the moment of slip. This ratio or its inverse provided the coefficient of friction or the slip ratio for a particular subject and surface condition. Twelve hours prior to a second recording session all subjects placed transdermal patches of 1.5 mg scopolamine behind each ear to reduce palmar sweating by blocking the muscarinic receptors of exocrine sweat glands. The subjects were re-tested following procedures that were identical to the first session. Scopolamine significantly reduced the friction of the skin on the smooth and 2-mm beaded surfaces, but the friction of the 3-mm beaded texture was unaffected. Scopolamine also caused subjects to increase both the peak and static grip forces for all the textures including the 3-mm beaded surface, suggesting that for two of the three surfaces they were responding to the increased slipperiness of the skin due to reduced sweat production.

Friction of the Human Finger Pad: Influence of Moisture, Occlusion and Velocity

“…Zackrisson et al [61] have measured grip coefficients of friction for hyperhidrosis patients, and shown that treatment to reduce sweat rates by botulinium toxin injections both affects the friction and can alleviate grip problems; in fact, the anhidrosis due to the injections tended to reduce the friction to levels expected for relatively dry skin. Smith et al [62] have shown that similar reductions in friction occur in grip experiments involving smooth surfaces when anhidrosis is induced by scopolamine injections.…”

A continuous measure of fingertip friction during precision grip

“…Up to now, various studies have considered the importance of the skin hydration level on performance during object manipulation. Smith et al (1997) investigated the influence of scopolamine on the prehensile force during object manipulation and showed an increase of this force due to a reduction of palmar sweating. In the same way, Zackrisson et al (2008) reported that a significant decrease of the CF and consequent significant increase of the grip force were observed when patients with very high sweating rate (hyperhidrosis) manipulated objects.…”

Finger pad friction and its role in grip and touch

“…The importance of sweat in determining the friction of the finger pad has been observed in a number of studies. Smith et al [77] described the results of applying scopolamine patches to subjects in order to suppress palmar sweating by blocking the muscarinic receptors of the eccrine sweat glands. On the basis of grip experiments it was found that, for some of the surfaces examined, there was an increase in the peak and static grip forces, which was interpreted as a response to an increase in the slipperiness of the skin.…”