Rui Ando (master's course) and Assistant Professor Norihiro Itaguchi (currently Keio University) of Shizuoka University have revealed that when the arm becomes heavier through experiments, the movement trajectory of the arm becomes higher, contrary to intuition. He pointed out that it may be difficult to use and cause fatigue.
The artificial hand has been developed in recent years, but there are many cases where the use is interrupted due to its weight.However, the effect of the weight of the prosthesis on the movement of the user is not clear.This time, the research group examined how the motion trajectory is adjusted when the weight of the arm changes.
In the experiment, participants reached out on the desk (reaching movement) and reached out to grab an object (reaching gripping movement). Every 10 trials, the weight wrapped around the arm was switched to weights of 0g, 100g, and 200g.
As a result, in both exercises, the motion trajectory was significantly higher under light conditions than under heavy conditions in the first trial immediately after the arm weight changed.This is a post-effect of the weight of the previous arm, and it is considered that the participants output muscles based on the condition of the arm in the previous trial.
In the ultimate gripping motion, the maximum wrist height in the 200th and 9th trials was higher than in the other conditions under the 10g condition.Participants seemed to select a high motion trajectory when their arms were heavy and succeeded in reaching and grasping motion, but did not recognize it in reaching motion.It is considered that the influence of the weight of the arm on the motion trajectory was small in the reaching motion with low required accuracy.
Since the muscle output increases as the movement trajectory increases, discomfort and fatigue may occur even when using an artificial hand in which the weight of the forearm changes.This achievement is expected to contribute to the development of a wide range of medical and industrial technologies related to human motor behavior, such as the development of easy-to-use artificial hands and the prevention of accidents during fatigue, in addition to the elucidation of the human motor control mechanism.
Paper information:[Experimental Brain Research] The heavier the arm, the higher the action: the effects of forearm-weight changes on reach-tograsp movements
