Analysis of “Invariant Characteristics” in the Motor Control of Down’s Syndrome and Normal Subjects

Abstract

Following Asatryan and Fei'dman (1965), two experiments were conducted to describe the so-called invariant mechanical properties underlying movement control in Down's syndrome and normal subjects. The invariant characteristic is a curve on a graph of joint torque versus joint angle. The task required subjects to maintain a steady joint angle against an external load (torque). Torque was systematically changed via partial unloading in order to obtain torque by length (joint angle) functions at three separate initial joint angles. Instructions required subjects "not to intervene" when unloading occurred in Experiment 1 and to "tense" their muscles prior to unloading in Experiment 2. Both normal and Down's syndrome groups revealed systematic torque by length functions that might be expected according to a simple mass-spring system model. Although the gross organization of movement in Down's syndrome subjects was nearly the same as normals, important differences between the two groups were found. Down's syndrome subjects revealed underdamped motions relative to normals (as shown by differences in the degree of oscillation about the final equilibrium position) and were less able to regulate stiffness (as shown by differences in slope of the torque by angle functions in Experiment 2). We promote the notion that damping and stiffness may be sensitive indices of hypotonia-the most common description of neuromuscular deficiency in Down's syndrome

Space–time behavior of single and bimanual rhythmical movements: Data and limit cycle model.

“…One appealing aspect of the model is that it formalizes and extends some of Feldman's (1966) early but influential work (see, e.g., Bmzi et al, 1976;Cooke, 1980;Kelso, 1977;Ostry & Munhall, 1985;Schmidt & McGown, 1980). Feldman (1966) presented observations on the execution of rhythmic movement that strongly suggested that the nervous system was capable of controlling the natural frequency of the joint using the so-called mvanant characterisucs--a plot of joint angle versus torque (see also Berkenblit, Feldman, &Fukson, 1986, Davis andKelso, 1982). But he also recognized that "a certain mechanism to counteract damping in the muscles and the joint" must be brought into play, in order to "make good the energy losses from friction in the system" (Feldman, 1966, p. 774).…”

Exploring effects of different treadmill interventions on walking onset and gait patterns in infants with Down syndrome

“…Children with DS usually walk at a slower speed, and produce a shorter step length and a wider step width. 9,10 This is due to their musculoskeletal and neuromuscular deficits such as decreased muscle strength, 11 hypotonia, 12 and increased muscle burst onset latencies. 13 As infants with DS can repeatedly practice alternating stepping patterns (a pattern similar to that of overground walking) and improve their leg muscle strength and limb coordination during treadmill training, they should produce more advanced gait patterns within a certain period after the training ends.…”

Avaliação do equilíbrio estático de crianças e adolescentes com síndrome de Down

“…Studies have suggested developmental changes such as sensory-motor abilities, muscle fatigue, exacerbated joint fatigue, hypotonia and cerebellar hypoplasia [6][7][8][9][10] . Kokubun et al 23 compared balance with unilateral support in DS children to that of children with other kinds of mental impairment.…”

“…Some aspects have been suggested as causes for the delay in the acquisition of motor skills in DS children. The main causes of these differences include an exacerbated weakness in the joints, muscle weakness, sensory-motor abilities, cerebellar hypoplasia, and hypotonia [6][7][8][9][10] . Dysfunctions in the postural control are often described in DS children and associated with motor coordination difficulties, problems with sensory-motor integration or simply with awkward movements.…”