Biomedical subjects

Richard E A van Emmerik

Publications and source records attributed to Richard E A van Emmerik.

5 recordsLinked to original sources

PubMed2006

Coordination variability around the walk to run transition during human locomotion.

Increases in movement variability have previously been observed to be a hallmark property of coordination changes between coupled oscillators that occur as movement frequency is scaled. Prior research on the walk-run transition in human locomotion has also demonstrated increases in variability around the transition region, supporting predictions of nonequilibrium phase transitions (Diedrich & Warren, 1995). The current study examined the coordinative patterns of both intra- and inter-limb couplings around the walk-run transition using two different temporal manipulations of locomotor velocity as a control parameter in healthy young participants (N = 11). Coordination variability did not increase before the transition. The nature of the change in continuous relative phase variability between gait modes was coupling-specific, and varying the time spent at each velocity did not have an overall effect on gait transition dynamics. Lower extremity inter-limb coordination dynamics were more sensitive to changes in treadmill velocity than intra-limb coordination. The results demonstrate the complexity of segmental coordination change in human locomotion, and question the applicability of dynamical bimanual coordination models to human gait transitions.

Adult↗

PubMed2005

Stride cycle influences on goal-directed head movements made during walking.

Horizontal head movements were studied in six subjects as they made rapid horizontal gaze adjustments while walking. The aim of the present research was to determine if gait cycle events alter the head movement response to a visual target acquisition task. Gaze shifts of approximately 40 degrees were elicited by a step change in the position of a visual target from a central location to a second location in the left or right horizontal periphery. The timing of the target position change was constrained to occur at 25%, 50%, 75% and 100% of the stride cycle. The trials were randomly presented as the subjects walked on a treadmill at their preferred speed (range: 1.25-1.48 m/s, mean: 1.39+/-0.09 m/s). Analyses focused on the movement onset latencies of the head and eyes and on the peak velocity and saccade amplitude of the head movement response. The head and eye movement onset latencies were not affected by either the direction of the target change or the point in the gait cycle during which the target relocation occurred. However, the presence of an interaction between the gait cycle events and the direction of the visual target shift for both the amplitude and peak velocity of the head movement response indicates that the head movement responses to visual target changes can be influenced by the phase of the gait cycle during which the target relocation takes place.

Adult↗

PubMed2005

Adaptations in interlimb and intralimb coordination to asymmetrical loading in human walking.

The purpose of this study was to examine both the intralimb (within a limb) and interlimb (between the right and left limbs) adaptations that occur in response to a unilaterally applied leg load as subjects walked at their preferred walking speed. It was hypothesized that this adaptation would alter interlimb coordination while intralimb coordination remained invariant. Subjects (n = 12) were required to walk on a treadmill at preferred walking speed. Bilateral 3-D kinematic data were collected while a load placed on the leg was increased. Gait adaptations to leg-loading were assessed through changes in coordination patterns between specific limb couplings. Continuous relative phase (CRP) was used to evaluate changes in limb coordination under each experimental load condition compared to a no load baseline condition. Both changes in magnitude of CRP (root-mean-square (RMS) analysis) as well as temporal changes in CRP across the stride cycle (cross-correlation) were assessed. Cross-Correlation values changed with load for all interlimb couplings assessed suggesting alterations in interlimb coordination across the stride cycle. CRP cross-correlation values were close to 1.0 in all the intralimb couplings examined, showing a relative invariance in intralimb coordination. Coordination changes in RMS were also observed for the interlimb couplings. RMS changes were also observed in the intralimb couplings on the loaded side. It appears that gait adaptations to a unilaterally applied leg load appear both at the intralimb and interlimb level. However, the majority of changes did appear at the interlimb level, where CRP as assessed through both cross-correlation and RMS measures changed. This study supports previous results that suggested a tighter coupling exists at the intralimb level, leaving the majority of gait adaptations to occur at the interlimb level. The observed adaptation in differences between interlimb and intralimb coordination may provide insight into gait adaptations in pathological gait.

Adult↗

PubMed2005

Gender differences in lower extremity coupling variability during an unanticipated cutting maneuver.

The purpose of this study was to determine if gender differences exist in the variability of various lower extremity (LE) segment and joint couplings during an unanticipated cutting maneuver. 3-D kinematics were collected on 24 college soccer players (12 M, 12 F) while each performed the cutting maneuver. The following intralimb couplings were studied: thigh rotation (rot)/leg rot; thigh abduction-adduction/leg abd-add; hip abd-add/knee rot; hip rot/knee abd-add; knee flexion-extension/knee rot; knee flx-ext/hip rot. A vector-coding technique applied to angle-angle plots was used to quantify the coordination of each coupling. The average between-trial standard deviation of the coordination pattern during the initial 40 % of stance was used to indicate the coordination variability. One-tailed t-tests were used to determine differences between genders in coordination variability for each coupling. Women had decreased variability in four couplings: 32 % less thigh rot/leg rot variability; 40 % less thigh abd-add/leg abd-add variability; 46 % less knee flx-ext/knee rot variability; and 44 % less knee flx-ext/hip rot variability. These gender differences in LE coordination variability may be associated with the increased incidence of ACL injury in women. If women exhibit less flexible coordination patterns during competition, they may be less able to adapt to the environmental perturbations experienced during sports. These perturbations applied to a less flexible system may result in ligament injury.

Adaptation, Physiological↗

PubMed2002

On the functional aspects of variability in postural control.

Current research in nonlinear dynamics and chaos theory has challenged traditional perspectives that associate high variability with performance decrement and pathology. It is argued that variability can play a functional role in postural control and that reduction of variability is associated with changes in balance with aging and neurological disease.

Aging↗