Showing papers by "Jaap H. van Dieën published in 2009"
TL;DR: The absence of a consistent pattern of correlations between lambda(L-stride) and MeanSD over the three directions suggests that variability and stability reflect, at least to a degree, different properties of the dynamics of walking.
242 citations
TL;DR: Longer data series led to more precise estimates for lambda(S-stride), lambda(L- Stride), and MaxFm, and all variables showed an effect of data series length, which suggested that when estimating and comparing these variables across conditions, data series covering an equal number of strides should be analysed.
213 citations
TL;DR: It is concluded that the advantages with respect to physical loading of sitting on an exercise ball may not outweigh the disadvantages.
108 citations
TL;DR: It is suggested that the limited variability of muscle activity at the EMG feedback site and at ipsilateral locations enhances fatigue development, as even at mean activity levels as low as 2% EMGmax, fatigue manifestations were found in the trunk extensors.
93 citations
TL;DR: This study showed the differences in ROM, NZ, and NZ stiffness between thoracolumbar regions of the human spine in axial rotation, flexion/extension, and lateral bending.
Abstract: STUDY DESIGN.: An in vitro study on human multilevel spinal segments. OBJECTIVE.: To determine the differences in biomechanical characteristics between 4 separate regions of the human spine and to provide quantitative information is derived on the range of motion (ROM), neutral zone (NZ), neutral zone stiffness (NZstiff), and flexibility (FLEX). SUMMARY OF BACKGROUND DATA.: Limited literature is available about the biomechanical behavior of different regions of the human spine, in particular with multilevel segments. Test setup en protocols were different between studies and therefore outcomes of separate regions are hardly comparable. METHODS.: A total of 24 spinal segments of 6 human cadaveric spines were prepared for biomechanical testing. Each specimen contained 4 vertebrae and 3 intervertebral discs: T1-T4, T5-T8, T9-T12, and L1-L4. Pure moments were applied to a maximum of 4 Nm in flexion/extension, lateral bending, and axial rotation. Displacement of individual motion segments was measured using a 3-dimensional movement registration system. ROM, NZ, NZstiff, and FLEX of the spinal regions were calculated from the acquired load-displacement data. RESULTS.: In axial direction, ROM and NZ decreased and NZ stiffness increased from high to low vertebral levels. For flexion/extension and lateral flexion highest ROM and NZ and lowest NZ stiffness values were found at the T1-T4 and L1-L4 regions. NZ magnitudes and NZ stiffnesses were negatively correlated (P < 0.05). Flexibility of the spinal regions was variable; no significant differences were found between the 4 spinal regions. CONCLUSION.: This study showed the differences in ROM, NZ, and NZ stiffness between thoracolumbar regions of the human spine in axial rotation, flexion/extension, and lateral bending. Separate multilevel spinal segments were tested in 1 study, and therefore characteristics of different regions are truly comparable.
73 citations
TL;DR: The aim of the present study was to determine whether TI can be obtained using a single inertial sensor (IS) on theBack, and to determine the optimal IS location on the back for the estimation of TI.
70 citations
TL;DR: There is evidence of objective signs of fatigue in some of the realistic, low-force tasks, and the intensity level appeared to be a main determinant here.
Abstract: Shoulder fatigue has been suggested to be a useful risk indicator for shoulder disorders in repetitive, low-force work tasks. In contrast to high-force or purely isometric tasks, it is unclear whether measurable fatigue develops in realistic low-force work. The question addressed in this review was: 'Is there evidence of objective signs of fatigue in the shoulder region in realistic, low-force work tasks?' Studies on objective measures of fatigue applied in realistic low-force work tasks were systematically reviewed, using a task duration of more than 1 h and an intensity level of less than 20% maximum voluntary contraction (MVC) for the median trapezius activation level as inclusion criteria. Thirteen studies were found to fulfil the criteria. All these studies addressed fatigue-related changes in the electromyographic signal in the descending part of the trapezius muscle. Seven did find a combination of frequency decrease and amplitude increase over time, which is generally considered as an objective manifestation of fatigue. Thus, there is evidence of objective signs of fatigue in some of the realistic, low-force tasks. The intensity level appeared to be a main determinant here. In the studies demonstrating signs of fatigue an intensity level of 15%MVC or more was used, while the intensity level in the studies with a negative result was generally lower.
67 citations
TL;DR: Load-splitting resulted in most cases in a reduction (8-32%) of peak L5/S1 compression forces and the magnitude of the reduction was roughly comparable to halving the load mass and depended on lifting technique and load width.
44 citations
TL;DR: No effect was found of the resistance-training program on isokinetic muscle strength of the back and shoulder muscles, nor on musculoskeletal discomfort during the simulated work tasks, and trained workers performed the lifting tasks for a longer time before reporting considerable discomfort.
22 citations
TL;DR: Older participants used toe landing more frequently and more consistently than young participants, and this preference for toe landing is suggested to reflect adaptive behavior to enhance gait stability, rather than an inability to use a heel landing.
21 citations
TL;DR: It is concluded that a movable backrest reduces the transmission of vibration through the trunk and that it reduces low back EMG.
Abstract: The aim of this study was to test the effect of a movable backrest on vibration transmission through the trunk during driving and on the physiological consequences thereof. Eleven healthy male subjects drove for about 1 h on normal roads with a movable and with a fixed backrest while surface electromyography (EMG) was measured at the level of the fifth lumbar vertebra (L5) and vertical accelerations were measured at the seat, backrest and at the spine at the levels of the second sacral vertebra (S2) and seventh cervical vertebra (C7). The movable backrest significantly reduced accelerations at C7 by up to 11.9% at the 5 Hz frequency band. The movable backrest also significantly reduced the coherence and transmission between S2 and C7 accelerations, but not the differential motion between these sensors. EMG at both sides of L5 was on average 28% lower when using the movable backrest. Spinal shrinkage was unaffected by backrest type. It is concluded that a movable backrest reduces the transmission of vibration through the trunk and that it reduces low back EMG. Car driving is associated with the risk of developing low back pain and this may be related to exposure to whole body vibration. This study found an effect of a simple ergonomics measure on the transmission of vibration through the trunk as well as on back muscle activation.
27 Apr 2009
TL;DR: It is concluded that ACL-deficient subjects show a task dependent increase in hamstrings co-activation, but its clinical significance remains to be shown.
Abstract: It has been reported that anterior cruciate ligament (ACL)-deficient subjects increase the level of hamstrings activation and this has been interpreted as a means to cope with increased anterior tibial laxity in the knee. This study aimed to establish to what extent co-activation strategies in ACL-deficient subjects are load level and knee angle dependent. Eleven chronic ACL-deficient and 15 control subjects were positioned in a range of postures and asked to exert a feedback controlled vertical ground reaction force (GRF; 30, 60% and maximum), while horizontal forces were not constrained. Surface electromyography of the leg muscles and GRF were measured. In postures with the knee over and in front of the ankle, ACL-deficient subjects generated, respectively, 2.4 and 5.1% MVC more hamstrings activation than control subjects. Enhanced hamstrings co-activation in ACL-deficient subjects was more apparent in extended than in flexed knee angles. For both ACL-deficient and control subjects, hamstrings co-activation was larger in males than in females. It is concluded that ACL-deficient subjects show a task dependent increase in hamstrings co-activation, but its clinical significance remains to be shown.