According to this study, the design of most computer mouse-devices today often cause physical problems in the neck-shoulder-arm region (I know; I'm experiencing them right now). The study then proposes an alternative mouse-design, which they call the Horse Concept.
This new concept is called Horse in view of its functional design: the palm of the hand as well as the middle three fingers "sit" on the main body while thumb and little finger rest at a lower level at the side as if supported by stirrups. Thumb and little finger work together to realize optimal control in the horizontal (X-Y) plane. The design of the Horse allows for the three middle fingers to adopt a flexed position to relax the tendons. A major part of these fingers rests in a more or less vertical position.