Effect of kinetic redundancy on hand digit control in children with DCD

Abstract

We investigated finger strength and the ability to control digit force/torque production in children with Developmental Coordination Disorder (DCD) using manipulative tasks with different kinetic redundancies (KNR). Age-related changes in finger strength and finger force/torque control in typically developing (TD) children were also examined to provide a developmental landscape that allows a comparison with children with DCD. Forty-eight TD children (7-, 9-, and 11-year-olds) and sixteen 9-year-old children with DCD participated in the study. Three isometric tasks with different KNR were tested: constant index finger pressing force production (KNR=0), constant thumb-index finger pinching force production (KNR=1), and constant thumb-index finger torque production (KNR=5). Each subject performed two conditions for each isometric task: maximum voluntary force/torque production and constant force/torque control (40% of maximum force/torque). The results showed that the maximum force/torque production increased and the variability of constant force/torque control decreased with age in all tasks in TD children. Children with DCD showed larger variability than TD children in the constant thumb-index finger pinching torque production. These results suggest that children with DCD, as compared to TD children, are capable of producing the same level of maximum finger force, but have poor control in manipulation tasks with a large number of kinetic redundancies. Keywords motor redundancy; finger force control; development; children; DCD For successful achievement of everyday manipulative tasks, the central nervous system (CNS) is required to control digit-tip forces and moments. During a simple multi-digit prehension task, the hand provides an infinite number of digit-tip contact force and torque solutions available to achieve the motor task. This problem is commonly referred to as motor redundancy [5;28], which requires the CNS to find a solution from the many available kinetic variables. Previous studies have addressed the problem of motor redundancy in manipulative tasks of adults, specifically during prehension of hand-held objects [24;25;29]. However, far less attention has been drawn to how children solve the problem of motor redundancy and no studies have examined how children with motor difficulties such as those with Developmental Coordination Disorder (DCD) [2] handle this problem.

Efeito da posição da articulação do cotovelo no controle de torque de supinação do antebraço em jovens adultos

“…However, when participants were asked to control torque at different submaximum levels, there was greater motor response variability. these results concur with findings of previous studies for tasks involving finger-pressure strength control 26 , two-fingered prehension in pinch 14 and torque in lateral pinch 4,19 .…”

“…two tasks involving isometric supination torque (tq) in lateral pinch (using the thumb pad and the radial side of the second phalanx of the index finger) were assessed with a customized torque transducer 4,18,19 . Subjects were asked to perform two isometric tasks: maximum voluntary torque in lateral pinch (tq maX ) and constant and continuous torque in lateral pinch (tq ConSt ).…”

“…In particular, manipulative tasks have been investigated in order to understand this inherent trait of the neuromotor system [4][5][6][7][8] . Because of its singular mechanical structure, the hand stands out as a "convenient" tool in the study of the problem of motor redundancy 9 .…”

Handwriting: Hand–pen contact force synergies in circle drawing tasks

“…The manifold is approximated linearly by the null space spanned by the orthonormal basis vector, e(Y), solving the following equation. Greater DV values represent a greater kinetic synergy between hand-pen contact forces (Oliveira et al, 2006;Shim et al, 2008). In other words, DV quantifies how well the four individual force components compensate for each other's errors to achieve the constant trajectory of circle drawing.…”

“…However, the same structure may also present control challenges to the CNS because of the extremely high motor redundancy inherent in its system (Chao and An, 1978;Dul et al, 1984;Oliveira et al, 2006). For example, when a hand holds a pen with multiple fingers, the motor task becomes kinetically redundant because there are more contact forces than the forces minimally necessary for the movement outputs of the pen (e.g., pen-tip force) (Shim et al, 2005a;Oliveira et al, 2006;Fernandes and Chau, 2008). Previous studies on multi-finger pressing and grasping have shown that the CNS prioritizes some sub-tasks critical for the achievement of redundant motor tasks to utilize the redundancy (Shim et al, 2003Gorniak et al, 2009;Zhang et al, 2009).…”