Kinsuk K. Maitra, Katherine Philips, Martin S. Rice; Grasping Naturally Versus Grasping With a Reacher in People Without Disability: Motor Control and Muscle Activation Differences. Am J Occup Ther 2010;64(1):95–104. https://doi.org/10.5014/ajot.64.1.95
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OBJECTIVE. We investigated motor control and muscle activation when reaching for and grasping objects with a reacher compared with the unaided hand.
METHOD. In a repeated-measures counterbalanced design, 41 healthy participants with no previous experience using a reacher were randomly assigned to a sequence of four conditions. Movements of the wrist and fingers were recorded using a three-dimensional Qualisys camera system for assessing reach and grasp. Muscle activations from finger and arm flexors and extensors were recorded by surface electromyography.
RESULTS. Participants exhibited a smaller grasp aperture, longer reaching time, and more muscle activity when they used a reacher.
CONCLUSION. Efficient motor control, which requires both time and practice, is needed to successfully use a reacher. Clients presented with reachers without sufficient time to develop motor skills unique to reacher use may be more likely to abandon this assistive device and fail to benefit from its function.
Condition A: reaching–grasping a golf ball
Condition B: reaching–grasping a baseball
Condition C: reaching–grasping a small Rubik’s Cube
Condition D: reaching–grasping a large Rubik’s Cube.
Peak velocity of reach. Peak velocity in a velocity profile of a movement is an indicator of the force that movement requires; the faster the movement is, the greater the force the system requires to generate movement (Flash & Hogan, 1985; Trombly & Wu, 1999). Peak velocity of reach was computed as meters per second (m/s).
Reach time. Reach time (in seconds) was measured using onset–offset criteria mentioned previously to estimate speed of movement.
Percentage of time to reach peak velocity (%). An efficient movement is usually characterized by a single bell-shaped velocity profile. If the shape of the bell is symmetrical, it means that the movement is preprogrammed and no corrections are needed at the end. However, as accuracy demands increase for successful completion of the movement, more visual or other feedback is necessary. This results in a velocity profile that becomes skewed at the deceleration phase. Normally, the peak of a velocity profile of a learned and practiced movement is between 30% and 50% of the total movement (Bullock & Grossberg, 1988; Nagasaki, 1989). Thus, a left shift of peak velocity means a right skewed deceleration profile, indicating a guided strategy. Conversely, a right shift of peak velocity means either a more ballistic strategy that requires no guidance (aimless fast pointing) or a highly learned strategy (fast piano playing; Trombly & Wu, 1999). Percentage of total reaching movement where the peak velocity occurred was computed.
Maximal grasp aperture (distance between thumb and index finger in meters throughout the reach and grasp task)
Peak velocity of grasp aperture (m/s)
Time to reach maximal grasp aperture.
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