Effect of object width on precision grip force and finger posture

Abstract

This study aimed to define the effect of object width on spontaneous grasp. Participants held objects of various masses (0.75 to 2.25 kg) and widths (3.5 to 9.5 cm) between thumb and index finger. Grip force, maximal grip force and corresponding finger postures were recorded using an embedded force sensor and an optoelectronic system, respectively. Results showed that index finger joints varied to accommodate the object width, whereas thumb posture remained constant across conditions. For a given object mass, grip force increased as a function of object width, although this result is not dictated by the laws of mechanics. Because maximal grip force also increased with object width, we hypothesise that participants maintain a constant ratio between grip force and their maximal grip force at each given width. Altogether we conclude that when the task consists in manipulating objects/tools, the optimal width is different than when maximal force exertions are required.

Using kinematic reduction for studying grasping postures. An application to power and precision grasp of cylinders

“…Conversely, when using the power grasp with wider diameters, subjects mostly decrease digit arching and closeness and increase opposition. These results are coherent with those from previous works (Cuijpers et al, 2004;Domalain et al, 2008;Meulenbroek et al, 2001;, as they show that the hand adapts its aperture to the object size, but provide far more detailed comprehensive information. Different weight effects were also identified depending on the grasp type performed for all RKVs except for finger adduction.…”

“…Hand posture introduces constraints on the strength that can be exerted to complete a given task (Domalain et al, 2008;Rossi et al, 2012;Shivers et al, 2002;Watanabe et al, 2005), and affects the distribution of contact pressure and comfort rating (Aldien et al, 2005;Youakim, 2009). Hand posture also affects tendon loads and excursions, and stresses on adjacent tissues such as synovial membranes and nerves (An et al, 1983;Lee et al, 2008), which is associated with the risk of developing work-related musculoskeletal disorders (WMSD) (Laoopugsin and Laoopugsin, 2012;Wells et al, 1994).…”

“…Previous studies have shown that object size and shape cause different grasp execution (Cuijpers et al, 2004;Domalain et al, 2008;Meulenbroek et al, 2001;: the hand adapts its aperture to the size and shape of the object in an attempt to avoid collisions, especially with the fingers; this adaptation is not uniform, but increases dramatically during the last phase of grasp execution; thick objects (envelop diameter > 4 cm) tend to be grasped with all digits, while only the thumb and the index and middle fingers are used to grasp thin objects. Fewer studies have addressed the effect of an object's weight on hand posture.…”

Manual strangulation: Experimental approach to the genesis of hyoid bone fractures

“…Domalain et al demonstrated that in order to maintain horizontally a rigid object of 2.25 kg and 7.5 cm between the thumb and first finger, without crushing it, a mean force of 21.8 N (AE3.2, 2.2 kg) is required [17]. The distance of 7.5 cm can correspond to the width of the laryngeal axis.…”

Effect of elliptic handle shape on grasping strategies, grip force distribution, and twisting ability

“…Without the knowledge of grip force that people can apply for varying grip conditions, the model is currently limited in its ability to predict maximum torque. Further studies that aim to predict grip force capability for varying handle shapes and corresponding hand postures (Kong et al 2007, Domalain et al 2008, Seo and Armstrong 2008, Lee et al 2009) would help improve the torque prediction capacity.…”