The Atlatl as a Cyborg Kinematic Device

The atlatl, or spear-thrower, is a primitive weapon, which is generally understood as a simple wrist lever. We propose to renew this interpretation by a simple kinematic analysis of the serial chain constituted by the arm, the forearm, the hand holding the atlatl and the dart, moving in a vertical plane. While the release velocity of a hand-delivered spear towards the target is made difficult due to the limited-joint range in wrist radial/ulnar deviation, the atlatl’s passive hook makes possible to overcome this difficulty. The atlatl can therefore be seen as a clever cyborg device, understood as a substitute of the hand with a special ability to orient the dart to be thrown. In a kinematic point of view, it realizes a shifting of the optimal throwing configuration from the upper-limb fully extended in a vertical position, badly adapted to human shoulder and wrist, to a much more efficient horizontal position. As a consequence, a summation of shoulder, elbow and wrist speeds results, leading to dart release velocities much greater than these got with a hand-delivered spear, while throw accuracy is kept. Because the atlatl’s learning is based on our natural ability to throw by comparison, for example, with the bow technology, and because its use is based more on gesture quality than on purely muscular power, the atlatl is according to us a remarkable historical example both of easy-to-learn and non-gendered cyborg device.