Showing papers by "Jaap H. van Dieën published in 2003"
TL;DR: It is proposed that motor control changes in patients are functional in that they enhance spinal stability and suggest an alternative model to explain the alterations of trunk muscle recruitment due to low-back pain.
609 citations
TL;DR: A theoretical framework is presented, in which comfort and discomfort were defined and the hypothetical associations with underlying factors were indicated, and the literature was reviewed to determine the relationships between objective measures and subjective ratings ofcomfort and discomfort.
Abstract: The concepts of comfort and discomfort in sitting are under debate. There is no widely accepted definition, although it is beyond dispute that comfort and discomfort are feelings or emotions that are subjective in nature. Yet, beside several subjective methodologies, several objective methods (e.g. posture analysis, pressure measurements, electromyography (EMG) are in use to assess sitting comfort or discomfort. In the current paper a theoretical framework is presented, in which comfort and discomfort were defined and the hypothetical associations with underlying factors were indicated. Next, the literature was reviewed to determine the relationships between objective measures and subjective ratings of comfort and discomfort. Twenty-one studies were found in which simultaneous measures of an objective parameter and a subjective rating of comfort or discomfort were obtained. Pressure distribution appears to be the objective measure with the most clear association with the subjective ratings. For other variables, regarding spinal profile or muscle activity for instance, the reported associations are less clear and usually not statistically significant. ©Medline
542 citations
TL;DR: Trunk muscle recruitment patterns in patients with low back pain are different from those in healthy control subjects, and the differences are likely to be functional with respect to enhancement of spinal stability in the patients.
Abstract: STUDY DESIGN: A comparative study of trunk muscle recruitment patterns in healthy control subjects and patients with chronic low back pain was conducted. OBJECTIVE: To assess trunk muscle recruitment in patients with low back pain. SUMMARY OF BACKGROUND DATA: Conflicting evidence has been reported on the level and pattern of trunk muscle recruitment in patients with low back pain. The disparities can be explained partly by methodologic differences. It was hypothesized that trunk muscle recruitment patterns may be altered in patients with low back pain to compensate for reduced spinal stability. METHODS: For this study, 16 patients with low back pain and 16 matched control subjects performed slow trunk motions about the neutral posture and isometric ramp contractions while seated upright. Ratios of electromyographic amplitudes and estimated moment contributions of antagonist over agonist muscles and of segmentally inserting muscles over muscles inserting on the thorax and pelvis only were calculated. In addition, model simulations were performed to assess the effect of changes in muscle recruitment on spinal stability. RESULTS: The ratios of antagonist over agonist, and of lumbar over thoracic erector spinae electromyographic amplitude and estimated moment contributions were greater in the patients than in the control subjects. The simulation model predicted that these changes would effectively increase spinal stability. CONCLUSIONS: Trunk muscle recruitment patterns in patients with low back pain are different from those in healthy control subjects. The differences are likely to be functional with respect to enhancement of spinal stability in the patients.
461 citations
TL;DR: The data support the interpretation of abdominal cocontraction during lifting as subserving spinal stability, and an alternative function of the increased trunk stiffness due to cocontractions might be to achieve more precise control over the trajectory of lifted weight in order to avoid sloshing of the water mass in the box and the consequent perturbations.
127 citations
TL;DR: The results suggest that deficits in bilateral force production are large enough to constitute an important performance-limiting factor and suggest that a reduced neural drive underlies this bilateral deficit.
Abstract: Purpose: Activity of the motor cortex in one hemisphere reduces the maximum motor outflow of homologous parts of the opposite hemisphere, causing a reduction in the maximum force a muscle can exert when the contralateral homologous muscle is activated concurrently. The purpose of this study was to establish whether this bilateral deficit is large enough to explain limitations in performance in bilateral exertions. Methods: Voluntary force production and neural drive during unilateral and bilateral exertions were compared in three experiments, consisting of unilateral maximum contractions, synchronous bilateral contractions, and asynchronous bilateral contractions of finger flexors and knee extensors. Results: Maximum voluntary force was overall about 7% lower in bilateral knee extension as compared with unilateral knee extension (P < 0.001). In finger flexion, a bilateral voluntary force deficit of as much as 20% was found (P = 0.001). Corresponding deficits in agonist EMG activity were also significant and on average found to be of similar size, though the magnitude of the bilateral deficit in EMG was not consistently related to the magnitude of the bilateral force deficit. In knee extension, a deficit in voluntary activation of 4% (P = 0.003) was demonstrated by means of superimposed tetanic stimulation. The magnitude of this deficit was correlated to the magnitude of the voluntary force deficit (r = 0.80, P = 0.002). The maximum rate of force development in bilateral knee extensions was 13% lower than in a unilateral knee extension (P = 0.002). Conclusion: These results suggest that deficits in bilateral force production are large enough to constitute an important performance-limiting factor. Furthermore, the data suggest that a reduced neural drive underlies this bilateral deficit.
92 citations
41 citations
TL;DR: It is concluded that, provided that empty containers are placed back onto the pavement as infrequently as possible, the introduction of the redesigned container could result in a reduction of the low back and shoulder load for refuse collectors.
Abstract: The objective of this study was to compare the mechanical and perceived workload when working with a redesigned two-wheeled container and working with a standard two-wheeled container for refuse collecting. The three changes in the design of the container were a displacement of the position of the centre of mass in the direction of the axis of the wheels, a slight increase in the height of the handle and a slight increase in the horizontal distance between the handle and the wheel-axis, and an increase in the diameter of the wheels. The volume of the container remained 0.240 m3. Nine refuse collectors performed some of their most frequent daily activities with both types of containers in the laboratory. Kinematics and exerted hand forces were assessed as input for detailed 3D biomechanical models of the low back and shoulder to estimate net moments at the low back and shoulders, compressive forces at the low back and contact forces at the glenohumeral joint. Also, the refuse collectors rated the ease of h...
30 citations
TL;DR: Load sharing of the index finger and middle finger was investigated during a pinching task and the effects were most apparent in the muscles responsible for the pinch force, the forearm muscles.
28 citations
TL;DR: In this paper, the authors investigated the effect of two important design parameters on joint loading and interpreted them in terms of optimising container design, and suggested that the design of Dutch two-wheeled containers can be improved by moving the COM of the loaded container in the direction of the axis of the wheels and by slightly raising the height of the handles.
23 citations
TL;DR: It appeared that a substantial reduction of lowback loading by favorable timing is not a realistic option, and designing tasks in such a way that they are located midship would reduce the 99th percentile of predicted low back moments.
13 citations
TL;DR: Unexpected lateral mass placement caused no clear increase in peak low back loading, and perturbed trunk movement and lower muscle forces indicated a decreased stability of the spine, which may imply an injury risk.
Abstract: Study Design. A repeated measurements experiment of spinal loading in healthy subjects. Objectives. To test whether unexpected lateral mass placement increases low back loading and trunk movement when subjects are lifting a mass in upright posture. Summary of Background Data. Epidemiologic studies suggest that sudden, unexpected loading will lead to low back pain. Also, asymmetric loading is considered to be harmful to the spine. It can be anticipated that unexpected asymmetric loading will increase the risk of injury even more. Methods. Ten subjects lifted in an upright posture a crate, in which a mass of 10 kg was placed laterally at the left side either expectedly or unexpectedly. The crate reaction forces, body movements, and trunk muscle activity were measured. From these, the L5-S1 net moments and muscle forces were estimated. Results. Unexpected lateral placement of the mass caused no clear increase in peak low back loading. The stiffness of the trunk was lower in the unexpected condition, which, in combination with inadequate net moments produced, resulted in movement of the trunk to the side of the displaced mass. Conclusions. Unexpected lateral mass placement does not increase the compression force. Perturbed trunk movement and lower muscle forces indicated a decreased stability of the spine, which may imply an injury risk.