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Jacques Duysens

Publications and source records attributed to Jacques Duysens.

18 recordsLinked to original sources
PubMed2006

Valgus bracing in patients with medial compartment osteoarthritis of the knee. A gait analysis study of a new brace.

A new valgus brace was evaluated in 15 patients with medial osteoarthritis of the knee and a varus leg axis. Significant improvement of pain and function were found after 6 weeks of brace treatment. Gait analysis showed that the brace had a tendency of lowering the peak varus moment about the knee. This effect was more profound in the presence of higher initial varus deformity angle of the knee. Furthermore, bracing led to a small decrease of knee extension at the end of the swing phase and an increase of walking velocity. The mechanisms identified by gait analysis in this study may be of clinical importance for future developments in brace treatment.

Braces↗
PubMed2006

Keep looking ahead? Re-direction of visual fixation does not always occur during an unpredictable obstacle avoidance task.

Visual information about the environment, especially fixation of key objects such as obstacles, is critical for safe locomotion. However, in unpredictable situations where an obstacle suddenly appears it is not known whether central vision of the obstacle and/or landing area is required or if peripheral vision is sufficient. We examined whether there is a re-direction of visual fixation from an object fixated ahead to a suddenly appearing obstacle during treadmill walking. Furthermore, we investigated the temporal relationship between the onset of muscle activity to avoid the obstacle and saccadic eye and head movements to shift fixation. Eight females (mean +/- SD; age = 24.8 +/- 2.3 years) participated in this experiment. There were two visual conditions: a central vision condition where participants fixated on two obstacles attached to a bridge on the treadmill and a peripheral vision condition where participants fixated an object two steps ahead. There were two obstacle release conditions: only an obstacle in front of the left foot was released or an obstacle in front of either foot could be released. Only trials when the obstacle was released in front of the left foot were analyzed such that the difference in the two obstacle conditions was whether there was a choice of which foot to step over the obstacle. Obstacles were released randomly in one of three phases during the step cycle corresponding to available response times between 219 and 462 ms. We monitored eye and head movements along with muscle activity and spatial foot parameters. Performance on the task was not different between vision conditions. The results indicated that saccades are rarely made (< 18% of trials) and, when present, are initiated approximately 350 ms after muscle activity for limb elevation, often accompanied by a downward head movement, and always directed to the landing area. Therefore, peripheral vision of a suddenly appearing obstacle in the travel path is sufficient for successful obstacle avoidance during locomotion: visual fixation is generally not re-directed to either the obstacle or landing area.

Adult↗
PubMed2006

Developmental trends in speed accuracy trade-off in 6-10-year-old children performing rapid reciprocal and discrete aiming movements.

Cyclic tasks are performed better than discrete tasks in adults but it is unknown whether this advantage is present in children as well. Three age groups of participants (6, 8, and 10 years old) executed cyclic and discrete aiming movements to two differently sized target using a Fitts task to examine the developmental effects on speed/accuracy trade-off. Children showed the same advantage of cyclic over discrete movements as previously demonstrated for adults but at a slower speed. The slope of the speed accuracy trade-off was similar in the three age groups in the cyclic as compared to the discrete control mode, suggesting that children learn both tasks equally well in this age range. The index of performance (IP) increased with age but not differently for the two control modes. Children showed clear differences between the kinematics of discrete and cyclic movements and these differences were similar to those seen in adults. Cyclic movements were faster, had higher IP, showed fewer changes in velocity and were more ballistic. Thus movement execution was different between the two tasks, consistent with the hypothesis that cyclic tasks make use of neural oscillators. The slower movement speed in young children is consistent with their limited ability to use open loop control.

Child↗
PubMed2006

High failure rates when avoiding obstacles during treadmill walking in patients with a transtibial amputation.

OBJECTIVE: To investigate if and to what extent patients with a transtibial amputation are less successful in avoiding unexpected obstacles while walking than healthy adults. DESIGN: Experimental 2-group design. SETTING: Dutch rehabilitation center. PARTICIPANTS: Eleven patients with a transtibial amputation and 14 healthy controls. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Subjects walked on a treadmill at .56m/s. In 2 series of 12 trials each, an obstacle was dropped in front of the prosthetic or the nonprosthetic leg of the amputation group and the left leg of the control group at different phases during the step cycle. It was noted which avoidance strategy was used (a long step strategy [LSS] or a short step strategy [SSS]) and whether the obstacle was avoided successfully or not. These data were expressed as a percentage of the total number of trials completed by each subject. RESULTS: With either leg, the amputation group made significantly more errors than the control subjects (prosthetic leg, 24%+/-17%; nonprosthetic leg, 21%+/-17% vs 2%+/-2% for the control group). Highest failure rates were in the amputation group when time pressure was high, requiring an SSS, especially on the prosthetic side. An LSS under time pressure, however, nearly always resulted in failure for both the prosthetic and nonprosthetic legs. Subjects with the longest time since amputation were most successful in avoiding unexpected obstacles. CONCLUSIONS: Under time pressure, patients with a lower-leg prosthesis perform best when they use their nonprosthetic leg as the lead limb in an SSS. The fact that some subjects with the longest time since amputation made no errors suggests that over many years it is possible to relearn the appropriate avoidance reactions sufficiently fast.

Adult↗
PubMed2006

A five-week exercise program can reduce falls and improve obstacle avoidance in the elderly.

BACKGROUND: Falls in the elderly are a major health problem. Although exercise programs have been shown to reduce the risk of falls, the optimal exercise components, as well as the working mechanisms that underlie the effectiveness of these programs, have not yet been established. OBJECTIVE: To test whether the Nijmegen Falls Prevention Program was effective in reducing falls and improving standing balance, balance confidence, and obstacle avoidance performance in community-dwelling elderly people. METHODS: A total of 113 elderly with a history of falls participated in this study (exercise group, n = 79; control group, n = 28; dropouts before randomization, n = 6). Exercise sessions were held twice weekly for 5 weeks. Pre- and post-intervention fall monitoring and quantitative motor control assessments were performed. The outcome measures were the number of falls, standing balance and obstacle avoidance performance, and balance confidence scores. RESULTS: The number of falls in the exercise group decreased by 46% (incidence rate ratio (IRR) 0.54, 95% confidence interval (CI) 0.36-0.79) compared to the number of falls during the baseline period and by 46% (IRR 0.54, 95% CI 0.34-0.86) compared to the control group. Obstacle avoidance success rates improved significantly more in the exercise group (on average 12%) compared to the control group (on average 6%). Quiet stance and weight-shifting measures did not show significant effects of exercise. The exercise group also had a 6% increase of balance confidence scores. CONCLUSION: The Nijmegen Falls Prevention Program was effective in reducing the incidence of falls in otherwise healthy elderly. There was no evidence of improved control of posture as a mechanism underlying this result. In contrast, an obstacle avoidance task indicated that subjects improved their performance. Laboratory obstacle avoidance tests may therefore be better instruments to evaluate future fall prevention studies than posturographic balance assessments.

Accidental Falls↗
PubMed2005

Advancing age progressively affects obstacle avoidance skills in the elderly.

The ability to adequately avoid obstacles while walking is an important skill that allows safe locomotion over uneven terrain. The high proportion of falls in the elderly that is associated to tripping over obstacles potentially illustrates an age-related deterioration of this locomotor skill. Some studies have compared young and old adults, but very little is known about the changes occurring within different age groups of elderly. In the present study, obstacle avoidance performance was studied in 25 young (20-37 years) and 99 older adults (65-88 years). The participants walked on a treadmill at a speed of 3 km/h. An obstacle was dropped 30 times in front of the left foot at various phases in the step cycle. Success rates (successful avoidance) were calculated and related to the time available between obstacle appearance and the estimated instant of foot contact with the obstacle (available response times or ARTs ranging from 200 to more than 350 ms). In addition, latencies of avoidance reactions, the choice of avoidance strategies (long or short step strategy, LSS or SSS), and three spatial parameters related to obstacle avoidance (toe distance, foot clearance, and heel distance) were determined for each participant. Compared to the young, the older adults had lower success rates, especially at short ARTs. Furthermore, they had longer reaction times, more LSS reactions, smaller toe and heel distances, and larger foot clearances. Within the group of elderly, only the 65-69 year olds were not different from young adults with respect to success rate, despite marked changes in the other parameters measured. In particular, even this younger group of elderly showed a dramatic reduction in the amount of SSS trials compared to young adults. Overall, age was a significant predictor of success rates, reaction times, and toe distances. These parameters deteriorated with advancing age. Finally, avoidance success rates at short ARTs were considerably worse in elderly participants who sustained recurrent falls in the six-month period prior to the assessment compared to those who sustained no or only one fall. An exercise program has been shown to improve avoidance success rates, especially at short ARTs, but the training effects on the determinants of success still need to be assessed.

Accidental Falls↗
PubMed2005

Phase-dependent modulation of short latency cutaneous reflexes during walking in man.

In reduced animal preparation (cat fictive locomotion) most of our knowledge on the phase-dependent modulation of cutaneous reflexes concerns early- (P1 responses) rather than medium-latency (P2) responses. In contrast, in humans, virtually only P2 responses have been studied because P1 responses are relatively rare in adults. In this work, human P1 and P2 responses following sural nerve stimulation were compared in BF (biceps femoris). Some 14% of all subjects showed P1 responses, which could be either suppressive or facilitatory. The suppressive responses were most common, and they occurred primarily at end swing. When a subject showed both suppressive P1 and P2 responses, the P2 suppressions were stronger than the P1 suppressions (as measured in the same phase at end swing). However, the P2 suppressions were less consistent across subjects than the P1 suppressions. In some subjects, there were also facilitatory P1 responses, mostly throughout stance (when facilitatory P2 responses occur as well). These facilitatory P1 responses were consistent across experimental conditions in these subjects. Similar to the cat, the facilitatory P1 responses were much smaller than the facilitatory P2 responses. It is concluded that P1 and P2 reflexes can appear independently from each other, but that their modulation in the step cycle is mostly quite similar in some phases of the step cycle (end swing).

Adult↗
PubMed2005

Restoration of weight-shifting capacity in patients with postacute stroke: a rehabilitation cohort study.

OBJECTIVES: To identify and interrelate recovery characteristics of voluntary weight shifting after stroke and to examine whether the assessment of weight shifting adds information about balance recovery compared with the assessment of quiet standing. DESIGN: Exploratory study using an inception cohort with findings related to reference values from healthy elderly persons. SETTING: Dutch rehabilitation center. PARTICIPANTS: Thirty-six inpatients (mean age, 61.8 y; mean time poststroke, 10 wk) with a first hemispheric intracerebral infarction or hematoma who were admitted to retrain standing balance and walking. INTERVENTION: Individualized therapy. MAIN OUTCOME MEASURES: Center of pressure (COP) displacements were registered during voluntary frontal-plane weight shifting guided by visual COP feedback using a dual-plate force platform. Besides the speed (number of weight shifts) and imprecision (normalized average lateral COP displacement per weight shift), the weight-transfer time asymmetry and the spatiotemporal distribution were determined. Assessments took place as soon as patients could stand unassisted for at least 30 seconds and at 2, 4, 8, and 12 weeks later. RESULTS: During the 12-week training period, the stroke patients increased both their speed (2.3 hits/30 s; 95% confidence interval [CI], 1.1-3.4) and precision (37.7 mm/hit; 95% CI, 10.4-65.0) of weight shifting. Although the speed appeared to stabilize at a suboptimal level after 8 weeks, precision reached normal reference values after 12 weeks. Both older age (>/=65 y) and the presence of visuospatial hemineglect negatively affected weight-shifting speed but not its relative improvement in time. During the training period, a small degree of weight-transfer time asymmetry persisted (mean change, .07; 95% CI, -.21 to .36), with an average of 23% slower weight shifts toward the paretic leg, but the spatiotemporal distribution remained symmetrical. The correlations between weight-shifting and quiet-standing control at the end of training were moderate (Spearman rho range, .50-.77). CONCLUSIONS: Even subjects with severe stroke who are selected for inpatient rehabilitation are able to improve their speed and precision of weight shifting by reducing the weight-transfer time toward both legs in a proportionate manner. The observed correlations between weight shifting and quiet standing indicate that the assessment of weight-shifting capacity provides unique information about balance recovery after stroke.

Adult↗
PubMed2005

Local vascular adaptations after hybrid training in spinal cord-injured subjects.

PURPOSE: Studies investigating vascular adaptations in non-exercised areas during whole body exercise training show conflicting results. Individuals with spinal cord injury (SCI) provide a unique model to examine vascular adaptations in active tissue vs adjacent inactive areas. The purpose of this study is to assess the effects of 4 wk of voluntary arm and electrically stimulated leg exercise (8-12 sessions) on vascular adaptations in active areas (thigh and arms) and inactive areas (calf). METHODS: Vascular characteristics were measured by plethysmography (blood flow and vascular resistance) and echo Doppler (diameter and flow-mediated dilation (FMD) after 13 min of ischemia). RESULTS: After training, increased thigh baseline and peak blood flow, decreased thigh baseline vascular resistance, and increased diameter of the common femoral artery were found in the stimulated thigh tissue. Forearm and calf arterial parameters and FMD, in both superficial femoral artery and brachial artery, did not change. The lack of activity in the calf and concomitant insufficient elevation of blood flow during training, and the high initial training status of the arms are suggested to explain the absence of vascular adaptations in these areas. CONCLUSION: The presence of vascular adaptations after only 4 wk of FES cycling indicates that adaptations occur in an early phase. In addition, 4 wk of whole body exercise training in SCI individuals leads to vascular adaptations in the exercised tissues (thigh) but not in nonstimulated passive tissue (calf).

Adaptation, Physiological↗
PubMed2004

Short-term effects of whole-body vibration on postural control in unilateral chronic stroke patients: preliminary evidence.

The short-term effects of whole-body vibration as a novel method of somatosensory stimulation on postural control were investigated in 23 chronic stroke patients. While standing on a commercial platform, patients received 30-Hz oscillations at 3 mm of amplitude in the frontal plane. Balance was assessed four times at 45-min intervals with a dual-plate force platform, while quietly standing with the eyes opened and closed and while performing a voluntary weight-shifting task with visual feedback of center-of-pressure movements. Between the second and third assessments, four repetitions of 45-sec whole-body vibrations were given. The results indicated a stable baseline performance from the first to the second assessment for all tasks. After the whole-body vibration, the third assessment demonstrated a reduction in the root mean square (RMS) center-of-pressure velocity in the anteroposterior direction when standing with the eyes closed (P < 0.01), which persisted during the fourth assessment. Furthermore, patients showed an increase in their weight-shifting speed at the third balance assessment (P < 0.05) while their precision remained constant. No adverse effects of whole-body vibration were observed. It is concluded that whole-body vibration may be a promising candidate to improve proprioceptive control of posture in stroke patients.

Chronic Disease↗
PubMed2004

Force levels in uni- and bimanual isometric tasks affect variability measures differently throughout lifespan.

Ninety-four participants (age 5-93 years) performed isometric force production tasks at five different levels of their maximum voluntary contraction (MVC) with either one or two index fingers. Research questions were whether variability measures in the bimanual task condition were different compared to the unimanual condition and whether this difference showed a developmental trend. Results showed that force regulation was more demanding during bimanual tasks (33% increase in error) During development signal-to-noise ratio (SNR) increased threefold from 5-12 years of age and again 60% from 12 years to adulthood. SNR for the elderly was comparable to values of 9 to 10-year-olds. SNR decreased in the bimanual task, particularly for the older persons. For adults and elderly, optimal SNR levels were observed around 36% of their MVC. In younger children, however, the inverted U-shape in the SNR over the full range of forces was not yet present.

Adolescent↗
PubMed2004

Are graphomotor tasks affected by working in the contralateral hemispace in 6- to 10-year-old children?

It has been shown that crossing the midline affects the performance of fine motor skills but the underlying mechanisms are not well understood. This issue is particularly important with respect to the development of motor activities such as writing or pointing in children. Forty-eight right-handed children performed goal-directed movements toward targets positioned either at the midline, or in the left (contralateral side), or right (ipsilateral) hemispace. Findings revealed that movements were more accurate in ipsilateral than in contralateral space and their overall accuracy increased by 42% between 6 and 10 years of age. Differences in movement time among hemispaces depended on the joints predominantly involved in producing the movements (wrist versus fingers). Lower accuracy of movements in contralateral workspace is also present when participants do not have to cross the midline but only move within this workspace. In motor proficient children, no developmental trends were found for these hemispace effects.

Brain↗
PubMed2004

Regulation of arm and leg movement during human locomotion.

Walking can be a very automated process, and it is likely that central pattern generators (CPGs) play a role in the coordination of the limbs. Recent evidence suggests that both the arms and legs are regulated by CPGs and that sensory feedback also regulates the CPG activity and assists in mediating interlimb coordination. Although the strength of coupling between the legs is stronger than that between the arms, arm and leg movements are similarly regulated by CPG activity and sensory feedback (e.g., reflex control) during locomotion.

Animals↗
PubMed2003

Reorganization of gait after limb-saving surgery of the lower limb.

OBJECTIVE: In this study, the concept of a cognitive dual-task performance and visual restriction during walking has been used to study the recovery of gait after limb-saving surgery in ten patients. DESIGN: All patients were recovering from some form of treatment to tumors of the lower limbs. Patients had to walk on a treadmill at their preferred speed. During the course of recovery, we measured normal walking, walking while performing an attention-demanding dual task, and walking during restricted vision, starting 5 mo postoperatively. RESULTS: Patients are able to reach an acceptable level of gait within 15 mo, especially when the basic locomotor activity (i.e., step-cycle duration, walking speed, gait symmetry) is taken into account. Nevertheless, the results showed that during the recovery, the patients were still hindered by the dual task and visual restriction while walking because they exhibited a decrease in step-cycle duration under these conditions. CONCLUSIONS: In general, an improvement in walking speed and a decrease in asymmetry was seen. On the other hand, patients still had a basically reduced control of gait after the 15-mo recovery period. This can be attributed to a lack of gait automatism caused by an irreversible loss of somatosensory input.

Adult↗
PubMed2003

Vibration-induced changes in EMG during human locomotion.

The present study was set up to examine the contribution of Ia afferent input in the generation of electromyographic (EMG) activity. Subjects walked blindfolded along a walkway while tendon vibration was applied continuously to a leg muscle. The effects of vibration were measured on mean EMG activity in stance and swing phase. The results show that vibration of the quadriceps femoris (Q) at the knee and of biceps femoris (BF) at the knee enhanced the EMG activity of these muscles and this occurred mainly in the stance phase of walking. These results suggest involvement of Ia afferent input of Q and BF in EMG activation during stance. In contrast, vibration of muscles at the ankle and hip had no significant effect on burst amplitude. Additionally, the onset time of tibialis anterior was measured to look at timing of phase transitions. Only vibration of quadriceps femoris resulted in an earlier onset of tibialis anterior within the gait cycle, suggesting involvement of these Ia afferents in the triggering of phase transitions. In conclusion, the results of the present study suggest involvement of Ia afferent input in the control of muscle activity during locomotion in humans. A limited role in timing of phase transitions is proposed as well.

Adult↗
PubMed2002

Patterns of bimanual interference reveal movement encoding within a radial egocentric reference frame.

Constraints on interlimb coordination have been studied intensively in past years with a primary focus on temporal features. The present study addressed spatial constraints or the degree of directional interference as a function of different line combinations between the upper limbs as well as the modulation of this interference as a result of different board orientations within the performer's workspace. This paradigm was used to address a prominent theme in motor neuroscience, namely whether (bimanual) movements are encoded within an allocentric reference frame (pattern of interference invariant with respect to extrinsic space) or within an egocentric reference frame (pattern of interference invariant relative to the center of the performer's action space, i.e., intrinsic). The observed patterns of interference revealed that movements are primarily encoded within a radial egocentric reference frame in which the performer is the center of action space. The present psychophysical findings converge with primate single-cell recording studies in which the direction has been identified as a primary movement parameter that is encoded in various brain regions, thereby constituting a principal determinant of bilateral interference.

Adult↗
PubMed2002

Effects of tendon vibration on the spatiotemporal characteristics of human locomotion.

The present study addressed the involvement of proprioceptive input of the muscle spindles in the spatiotemporal control of human locomotion. Blindfolded subjects walked along a walkway while tendon vibration, a powerful stimulus of Ia afferents, was applied to various muscles of the lower limb. The effects of tendon vibration were measured on joint kinematics and on intralimb and interlimb coordination. Tendon vibration of the tibialis anterior during locomotion led to a decreased plantar flexion at toe-off, whereas vibration of the triceps surae led to a decreased dorsiflexion during swing. Vibration of the quadriceps femoris at the knee led to a decreased knee flexion during swing. These local effects of vibration can be explained in the light of a lengthening illusion of the vibrated muscle in that phase of the gait cycle where the muscle is lengthened. Tendon vibration did not affect the qualitative features of intralimb coordination. With respect to interlimb coordination, only vibration of the biceps femoris showed a significant increase in phase lead of the vibrated limb. The present results suggest the involvement of Ia afferent input in the online control of joint rotations. Additionally it is hypothesized that the proprioceptive input of biceps femoris might be involved in the control of coordination between the limbs, whereas the coordination between the segments of one limb appears to be unaffected by disturbance of muscle spindle input of one muscle.

Adult↗