Beverly D. Ulrich

Understanding movement control in infants through the analysis of limb intersegmental dynamics

One important component in the understanding of the control of limb movements is the way in which the central nervous system accounts for joint forces and torques that may be generated not only by muscle actions but by gravity and by passive reactions related to the movements of limb segments. In this study, we asked how the neuromotor system of young infants controls a range of active and passive forces to produce a stereotypic, nonintentional movement. We specifically analyzed limb intersegmental dynamics in spontaneous, cyclic leg movements (kicking) of varying intensity in supine 3-month-old human infants. Using inverse dynamics, we calculated the contributions of active (muscular) and passive (motion-dependent and gravitational) torque components at the hip, knee, and ankle joints from three-dimensional limb kinematics. To calculate joint torques, accurate estimates were needed of the limbs anthropometric parameters, which we determined using a model of the human body. Our analysis of limb intersegmental dynamics explicitly quantified the complex interplay of active and passive forces producing the simple, involuntary kicking movements commonly seen in 3-month-old infants. our results revealed that in nonvigorous kicks, hip joint reversal was the result of an extensor torque due to gravity, opposed by the combined flexor effect of the muscle torque and the total motion-dependent torque. The total motion-dependent torque increased as a hip flexor torque in more vigorous kicks; an extensor muscle torque was necessary to counteract the flexor influences of the total motion-dependent torque and, in the case of large ranges of motion, a flexor gravity torque as well. Thus, with changing passive torque influences due to motions of the linked segments, the muscle torques were adjusted to produce a net torque to reverse the kicking motion. As a consequence, despite considerable heterogeneity in the intensity, range of motion, coordination, and movement context of each kick, smooth trajectories resulted from the muscle torque, counteracting and complementing not only gravity but also the motion-dependent torques generated by movement of the linked segments.

Perceptions of Physical Competence, Motor Competence, and Participation in Organized Sport: Their Interrelationships in Young Children

Abstract This study examined the interrelationships among perceived physical competence, motor competence, and participation in organized sport in young children. Males and females in Grades K through 4 (n = 250) were given The Perceived Competence Scale for Children (Harter, 1979) or The Pictoral Scale for Perceived Competence and Social Acceptance for Young Children (Harter, Pike, Efron, Chao, & Bierer, 1983), a 9-item motor competence assessment battery, and a questionnaire regarding their participation in sport. Results revealed that perceived physical competence for children in these grade levels was not significantly related to their participation in organized sport programs. Motor competence was significantly related to participation in that participants in organized sport programs performed selected gross motor tasks better than did nonparticipants. Further, childrens reported perceptions of physical competence were significantly related to their demonstrated motor competence. Discussion focused ...

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking

This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45 degrees ), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints-the intrinsic limb dynamics-in creating coordinated limb behavior out of nonspecific muscle activations.

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: III. Age-Related Differences in Limb Control.

In this article, the development of the increasingly differentiated control of the joints necessary to transform the spontaneous leg movements of early infancy into adaptive and functional actions is described. The hypothesis-that increasing joint control requires the capability for disassociation of joint action, the active modulation of joint stiffness, and a transition from proximal to distal control of the joints-is proposed. Kinematic and kinetic analyses of the vertical kicks of infants 2 weeks, 3 months, and 7 months of age (as well as a comparative group of adults) indicated increasing joint independence as well as phase-dependent and joint-dependent control modifications. The kicks of the younger infants were dominated by a proximal control strategy and minimal adjustments of the limb energetics during the flexion and extension phases of the kick. By 7 months of age, much larger modulations of the kick phases were observed as well as increasing evidence of distal control. These results revealed kinematic and kinetic patterns of emerging limb control between 2 weeks and 7 months of age.

ALTERNATING STEPPING PATTERNS: HIDDEN ABILITIES OF 11-MONTH-OLD INFANTS WITH DOWN SYNDROME

Normally developing infants can produce organized alternating stepping patterns long before they stand alone or attempt to walk, if supported upright on a motorized treadmill. The purpose of this study was to examine whether infants with Down syndrome, who begin to walk at a much later age than non‐disabled infants, could produced alternating steps in a similar way. Six of the seven 11‐month‐old infants studied responded to the treadmill stimulus by producing alternating steps. This suggests that the basic neural substrate necessary for upright locomotion is available long before walking occurs in infants with Down syndrome, as it is in normally developing infants. The infants in this study began to walk at an average of 13·3 months after demonstrating the ability to produce treadmill steps.

Chapter 17 Dynamic Systems Approach to Understanding Motor Delay in Infants With Down Syndrome

Abstract Researchers have documented that infants with Down syndrome (DS) acquire motor skills much more slowly than nonhandicapped (NH) infants. Several structural deficits common to infants with DS have been identified and offered as explanations for the consistent delay, including reduced brain weight, lower levels of the neurotransmitter 5-hydroxytryptamine, hypotonia, and joint laxity. This information describes the “component subsystems” the infant has to work with- but it does not explain how or why these subsystems ultimately do cooperate to allow new behaviors to emerge. A dynamic systems approach shifts the emphasis from description to understanding what causes transitions to new movement patterns. In this chapter we will describe how dynamic systems theory can guide research concerning the acquisition of motor skills in handicapped infants. We will use examples from our experiments on the emergence of stepping in infants with DS to support the utility of this approach.

Developmental Gross Motor Skill Ratings: A Generalizability Analysis

Abstract Elementary physical education instructors and movement development clinicians frequently employ movement observation as their primary assessment strategy. The purpose of this study was to determine the minimal conditions of observation needed to obtain generalizable results across observers, trials, and subjects for the hop, jump, and run. The developmental sequences developed at Michigan State University were used as the observation system. Twelve children in the age range of 33–111 months were rated on five trials by 15 observers. The sample consisted of an equal number of males and females and did not involve children with handicapping conditions. The results suggest that when observers receive 1 hour of training for each skill, one observer and three trials are needed for evaluating the hop (.88), while three observers and three trials are required for the jump (.83). None of the nine measurement conditions resulted in acceptable (.80) generalizability for the run.