PubMed Health⌕ Search

Biomedical subjects

E Thelen

Publications and source records attributed to E Thelen.

At least 37 records · Page 2Linked to original sources
PubMed1991

Hidden skills: a dynamic systems analysis of treadmill stepping during the first year.

When prelocomotor infants are supported on a motorized treadmill, they perform well-coordinated, alternating stepping movements that are kinematically similar to upright bipedal locomotion. This behavior appeared to be a component of independent walking that could not be recognized without the facilitating context of the treadmill. To understand the ontogenetic origins of treadmill stepping and its relation to later locomotion, we conducted a longitudinal study using an experimental strategy explicitly derived from dynamic systems theory. Dynamic systems theory postulates that new forms in behavior emerge from the cooperative interactions of multiple components within a task context. This approach focuses on the transitions, often nonlinear, where one preferred mode of behavior is replaced by a new form. Specific predictions about these transitions help uncover the processes by which development proceeds. Chapters II, III, and IV introduce dynamic principles of pattern formation and their application to development. In our application of these principles, we tested nine normal infants twice each month beginning from month 1 in a task where the treadmill speed was gradually scaled up and in an additional condition where each leg was driven by the treadmill at a different speed. Kinematic variables were derived from computerized movement analysis equipment and videotaped records. We also collected a number of anthropometric measurements, Bayley motor scores, and a behavioral mood scale for each month. Several infants stepped on the treadmill in their first month, but in all infants performance showed a rapidly rising slope from month 3 to month 6. Infants also showed corresponding improvement in adjustments to speed and relative coordination between the legs. In dynamic terminology, we found evidence that alternating stepping on the treadmill became an increasingly stable attractor during the middle months of the first year. Dynamic predictions that transitions would be characterized by increased variability and sensitivity to perturbation were borne out. Identifying the transitions enabled us to suggest a control parameter or variable moving the system into the stable response to the treadmill. This appeared to be the waning of flexor dominance in the legs during posture and movement that allowed the leg to be stretched back on the treadmill and so elicited the bilaterally alternating response. Further studies are needed to test this hypothesis. This dynamic analysis confirmed earlier suggestions that skill in general, and locomotion in particular, develops from the confluence of many participating elements and showed how emergent forms may result from changes in nonspecific components. A dynamic approach may be useful for understanding ontogenetic processes in other domains as well.

Exercise Test↗
PubMed1990

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 limb's 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.

Journal Article↗
PubMed1990

A dynamical systems approach to motor development.

The study of motor development has long influenced the clinical practice of physical therapy. We first review the contributions and deficiencies of two traditional maturational and reflex-based models of motor development. Second, we describe basic principles of kinematic and kinetic analyses of movement and show how we have applied these techniques to understand infant stepping and kicking. Third, we propose a theory of motor development based on a dynamical systems perspective that is consistent with our infant studies. Finally, we explore the implications of the model for physical therapists.

Child Development↗
PubMed1987

Bilateral coordination in human infants: stepping on a split-belt treadmill.

A motorized treadmill often elicits locomotor-like alternate stepping in 7-month-old infants who normally perform few, if any, stepping movements. The step cycle duration is a function of the speed of the treadmill. When infants were held so that each leg was on a separate treadmill belt, each of which was driven at a different speed, the overall cycle duration was intermediate between the cycle durations at the fast or slow speeds alone. Infants shortened the stance on the slow belt and increased the stance on the fast belt to maintain regularly alternating steps. Even before voluntary locomotion, both legs acted in a cooperative manner, with the dynamic status of one limb affecting the timespace behavior of the opposite limb.

Female↗
PubMed1987

Relationship between newborn stepping and later walking: a new interpretation.

The relationship between newborn stepping and later walking was examined by means of new kinematic and electromyographic data. Stepping movements of a group of 18 normal infants were compared at one and two months of age, at one and two months before the first independent steps, and at the month when these first steps occurred. Stepping in the first month was characterized by tight synchronization of hip, knee and ankle movements, but as early as two months the ankle-joint began to move out of phase with the hip and knee. Before independent walking a more adult-like pattern continued to emerge, with the knee leading the hip in flexion. However, with the onset of walking, primitive characteristics of newborn stepping remained, including ankle hyperextension at the end of the step, hyperflexion of the hip and knee and excessive muscle activation. These results suggest that mature walking may evolve from the newborn stereotyped movement pattern. It is suggested that these gradual changes in the organization of the step are evoked by the dynamic functional demands of upright locomotion, in addition to balance, postural control and strength development in the first year of life.

Adult↗
PubMed1986

Treadmill-elicited stepping in seven-month-old infants.

When infants begin to walk independently, their step patterns, while not fully mature, are different in kinematic details from those of newborn stepping and supine kicking. 6 7-month-old infants, who performed little or no stepping movements, were supported over a small, motorized treadmill. All showed immediate alternating stepping. These movements were more similar to adult-like steps than newborn steps. The implications of eliciting a more mature pattern by the treadmill are discussed. Although infants normally perform few steps at this age, the underlying mechanism has not "disappeared."

Child Development↗
PubMed1985

Developmental origins of motor coordination: leg movements in human infants.

The development of coordination of leg movements of human infants is discussed from the perspective of dynamic motor theory. Even in the newborn period, leg movements have topographical and temporal organization, but it is global and inflexible. During the first year, limb segments become both disassociated from these global synergies and reintegrated into more complex coalitions. Growth-related changes in the biodynamic properties of the body segments may be as important as neurological maturation in determining the movement outcomes and may help explain the spurts, regressions, and asymmetries seen in early infancy.

Biomechanical Phenomena↗
PubMed1983

Shifting patterns of bilateral coordination and lateral dominance in the leg movements of young infants.

Patterns of interlimb coordination and lateral preference of spontaneous leg kicks were described for 8 normal human infants observed biweekly from 2 to 26 weeks of age. Newborn infants showed a high percentage of alternating movements, which were often supplanted by unilateral movements between 1 and 4 months. Simultaneous (in-phase) kicks matured later than alternating kicks. No consistent lateral preferences were detected. The developmental course was marked by variability and discontinuities within each infant. We propose that asynchronous and asymmetrical maturation of subcortical tracts and/or muscle strength could account for these behavioral shifts.

Arousal↗
PubMed1983

Learning to walk is still an "old" problem: a reply to Zelazo (1983).

Zelazo (1983) proposes that two cognitive prerequisites are necessary for the development of locomotion: The conversion of neo-natal reflexive stepping into instrumental behavior and a shift from stereotypical to relational play. I argue that these cognitive assumptions are unnecessary. The disappearance of neo-natal stepping can be explained as a result of increasing leg mass, and the retention of this reflex with practice may be simply an exercise effect. Comparative and evolutionary evidence suggests that locomotion is not associated with abstract reasoning ability. Learning to walk is a complex, gradual process of maturation of motivation, the integration of subcortical pattern-generating centers with the neural substrate for control of posture and balance, and important changes in body proportions and bone and muscle strength. The control of walking is likely the province of mechanism phylogenetically more primitive than the human cerebral cortex. There is no need to invoke cortical explanations when more simple ones are sufficient.

Journal Article↗
PubMed1983

The organization of spontaneous leg movements in newborn infants.

Spontaneous, supine kicking in newborn (2- and 4-week-old) infants is described in terms of its temporal structure, interjoint coordination, and muscle activation characteristics as measured by surface electromyography. Phasic kick movements shoed a constrained temporal organization in the movement, but not the pause phases. Hip, knee, and ankle joints moved in temporal and spatial synchrony, and all three joints showed a rhythmical or periodic organization over time. EMGs revealed antagonist coactivation at the initiation of the flexor movement, but little or not extensor activity. The dorsal muscles, the gastrocnemius and hamstrings, showed less activity than the ventral pair, tibialis anterior and quadriceps. Burst and onset-to-peak durations were also constrained. As a result of neural mechanisms and biomechanical forces, newborn leg movements are structured muscle synergies. This organization has implications both for newborn functioning and for later development.

Journal Article↗
PubMed1983

From spontaneous to instrumental behavior: kinematic analysis of movement changes during very early learning.

3-month-old infants who can activate a mobile with their spontaneous leg kicks increase their kick rate over baseline. Kinematic analyses of the temporal and topographic characteristics of reinforced leg kicks were compared with those of infants who saw noncontingent mobile movement. In both experimental and control groups, the flexion and extension movement phases of the kick remained remarkably invariant in duration. Pauses between movements varied inversely with rate. Kick amplitude increased with increasing rate except in the extinction phase, where in some infants, kicks became less frequent but more forceful. Movement duration was unaffected by reinforcement condition. By varying amplitude and frequency domains, infants adjusted movement by neuromuscular mechanisms similar to those of mature humans. The experimental imposition of a voluntary component on spontaneous kicking did not alter the modifiability of the movement control parameters.

Conditioning, Operant↗
PubMed1982

Effects of body build and arousal on newborn infant stepping.

Newborn stepping is widely believed to be a "primitive reflex" whose disappearance signals cortical maturation. Observations of normal newborns showed that the number of steps was directly related to generalized behavioral arousal. In less highly distressed infants, those who were relatively heavier for their length stepped less. These results challenge the view that stepping is reflexively released by the upright posture and support the hypothesis that the movements disappear because infants' muscle strength may not be sufficient to lift their increasingly heavy legs.

Anesthesia, Obstetrical↗
PubMed1981

Kicking, rocking, and waving: contextual analysis of rhythmical stereotypies in normal human infants.

I analysed the triggering contexts of over 14,000 bouts of rhythmical stereotypies of the legs, arms, and whole torso observed in 20 normal infants during their first year. Infant stereotypies were elicited by a wide variety of contexts including non-alert states, interactions with the caregiver and other persons, feeding situations, object interest, and kinaesthetic changes. The frequency of stereotypy in all contexts was a function of age. Non-alert states and interactions with the caregiver were disproportionately associated with leg and torso stereotypies. The relationship between these human stereotypies and the function and control of stereotyped behavior in other species is discussed.

Age Factors↗
PubMed1979

[Results of arthrodesis of the ankle joint (author's transl)].

We present a check-up study of 47 arthrodeses of the ankle joint, partly in combination with an arthrodesis of the subtalar joint. By resection-compression-arthrodesis following Charnley-Horwitz-Adams we reached a bony fusion of the ankle joint in all cases. 83% of our cases showed a good or at least fair result. The remaining patients complained of painful walking in spite of orthopaedic shoes. In these cases a further fusion of subtalar joints especially of the talo-navicular joint should be considered.

Accidents, Occupational↗
PubMed1979

Rhythmical stereotypies in normal human infants.

Naturalistic, longitudinal observations of 20 normal infants biweekly during their first year showed that they performed a great quantity and variety of rhythmical and highly stereotyped behaviours. Forty-seven movement patterns are described involving the legs and feet; the head and face; the arms, hands, and fingers; and the whole torso in various postures. These behaviours showed developmental regularities as well as constancy of form and distribution. Groups of stereotypies involving particular parts of the body or postures had characteristic ages of onset, peak performance, and decline. The onset of particular stereotypy groups was highly correlated with motor development. It is proposed that rhythmical stereotypies are manifestations of incomplete cortical control of endogenous patterning in maturing neuromuscular pathways.

Age Factors↗