Biomechanics of reaching: clinical implications for individuals with acquired brain injury

Purpose : Outline the biomechanics of reaching both in healthy individuals and in individuals with acquired brain injury (ABI), and to discuss the clinical implications for using valid biomechanical models to assess reaching. Methods : A review of current literature, including a MEDLINE search using keywords of reaching, ABI, stroke, biomechanics and motor control. Results : Current assessments of the upper extremity in ABI are focused on single-joint characteristics of range of motion, strength and spasticity. However, reaching is a functional multijoint task requiring interjoint coordination in addition to feedback and feedforward control to position the hand optimally at a desired location so that it may interact with the environment. From the literature, biomechanical measures of reaching such as movement time, movement distance and interjoint coordination have been shown to discriminate changes to hand path quality following brain injury. These measures have also been shown to correlate with measures of sensorimotor function (e.g. Fugl-Meyer) in the upper extremity. Conclusions : Further development of reliable and valid multi-joint biomechanical evaluations is required, particularly for natural and goal-oriented reaching movements. The biomechanical assessment of reaching in ABI can provide an understanding of the specific deficits in physiological structures or motor planning underlying altered reaching ability, assist in the evaluation of new therapies, and characterize the recovery process following ABI.