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The effect of small changes of seat-back inclination on spine kinematics
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Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
Twelve healthy subjects (HS) and sixteen stroke patients presenting with a stiff knee gait were recruited. Wext was computed from the 3D ground reaction forces (GRFs, 100 c.p.s.) on a force measuring treadmill (Dierick 2004). Numerical integrations of the 3D accelerations gave the 3D speeds and the vertical displacement of the COMb, allowing the computation of the kinetic energy (Ek) and the gravitational potential energy (Ep). Positive (Wk+, Wp+) and negative works (Wk-, Wp-) were respectively obtained by adding the increments and decrements on Ek and Ep curves. By adding Ek and Ep, the total mechanical energy (Eext) was obtained, allowing the computation of Wext+ and Wext-. When the pathological leg supported the body weight, Wext+ and Wext- were normal (respectively 0.03±0.02 and 0.07±0.04Jkg -1). When the healthy leg supported the body weight, Wext+ was greater in patients (0.11±0.08 Jkg -1 , p = 0.013) than in healthy subjects (0.03±0.03 Jkg -1 ). This increase was mainly explained by an increase of Wp+ (0.15±0.09 vs 0.07±0.04 Jkg -1, p=0.009). When the pathological leg was in front during the double support, Wextwas greater in patients (0.11 ±0.06 Jkg -1 , p = 0.013) than in healthy subjects (0.05±0.03 Jkg -1). This increase was mainly explained by a nearly significant increase of Wp- (0.13±0.07 vs 0.09±0.03 Jkg -1 , p =0.065). On one hand, Wext+ of patients was increased and mainly produced by healthy limb muscles, to raise the COM b and make the foot clearance easier. On the other hand, Wext- was increased to absorb energy during the double support. The study of positive and negative works should improve our knowledge of the pathological gait mechanics.
5.13. Spine Kinematics 4039 Tu, 16:00-16:15 (P24) The effect o f small changes o f seat-back inclination on spine kinematics S. Adler, N. Piehler, J. H~nniger, R. Blickhan. Chair ef Motion Science,
Institute of Sports Science, Friedrich-Schiller-University, Jena, Germany Introduction: The influence of seat-back inclination on spinal loading and muscular activity has been widely studied [Harrison, Harrison, et al., 1999). Most of the studies, however, assessed different inclinations separately with the test person having to leave the seat between trials. This study aims to describe the effect of small changes of seat-back inclination on spine kinematics while the subject remains seated. Methods: 19 healthy adults (12 male, 7 female, age: 25.1±3.4 years; height: 177.2±7.4 cm; weight: 69.8±10.1 kg) were investigated during a 30 minute simulated driving test. Upper body movement and contact pressure were recorded. Seat-back inclination was varied every five minutes (18, 21, 24, 21, 18 degrees). [RB1] Results: (1) Posture and contact pressure show a high correlation. A reduction of lumbar lordosis and thoracic kyphosis results in an increased contact pressure at the back-rest and vice versa. Pressure under the ischial tuberosities is inversely related to the sum of back-rest pressure. (2) Posture and pressure readings change with altered seat-back inclination, but changes do not correlate with seat-back inclination. Head posture is unaffected by inclination changes. Discussion: (1) Because of the close relationship between posture and contact pressure, postural adaptations can be evaluated using continuous pressure measurement. Pressure under the ischial tuberosities is posture independent but is inversely related to the sum of back-rest pressure. This information helps to optimize the design of backrests to minimize ischemia of buttock tissue. (2) Posture is different for comparable seat-back inclinations, since posture and pressure readings differ significantly. Presumably, the fixed contact point of the ischial tuberosities and the initial pelvic angle, which are altered in recent studies due to repositioning of the subject between trials, are the main reasons for the observed kinematics. Conclusion: Spinal alignment and kinematics can not only be explained by seat-back angle. Current models must be modified to adequately describe spine kinematics for seated subjects. References Harrison D.D., Harrison S.O., et al. (1999). Sitting biomechanics part I: review of the literature. J Manipulative Physiol Ther, 1999; 22(9): 594~09.
Oral Presentations 4334 Tu, 16:15-16:30 (P24) Differences in lumbar spine motion pattern of weight-lifters and normal subjects performing freestyle lifting trials E MSrl 1, I. Bradl 2,3, R. Blickhan 4. 1Forschungsgesellschaft fEtr
angewandte Systemsicherheit und Arbeitsmedizin mbH, Erfurt, Germany, 2Berufsgenossenschaft Nahrungmittel und Gastst~tten, Prevention, Preventive Biomechanik, Erfurt, Germany, 3Friedrich-Schiller-University Jena, Clinic for accident surgery, motor research group, Jena, Germany, 4Friedrich-Schiller-University Jena, Institute of sport science, motion science, Jena, Germany Data of detailed intersegmental motion of the lumbar spine in daily-life-activities is rare. Most studies are in vitro or took under hardly restricted laboratoryconditions (X-ray or MRI). The aim of our study was to measure intersegmental lumbar spine motion patterns while lifting and compare motion strategies of different groups of subjects. The validity of the used method was analyzed by open MRI and rated as good. 11 subjects and 10 weight-lifters had to lift boxes choosing their favorite lifting technique. Box weight was random up to 15 kg for subjects and up to 60 kg for weight-lifters. Motion of lumbar spine was measured using infrared-light-based motion capturing and a skin-marker-method. Co-ordinates were transformed to 3-D Cardan-angles. In different lifting techniques (squat/stoop) different lumbar motion pattern were found: In squat-lifting (4 subjects) small range-of-motion on all lumbar levels were observed. In stoop-lifting (4 subjects) range-of-motion of motion segments is at average 3.25 times larger. 3 subjects performed a mixturetechnique. 9 out of 10 weight-lifters performed a squat-lifting-technique using also small range-of-motion. Spatial co-ordination of motion segments differs between this groups. Here the squat-lifters perform phases of very small motions of lumbar spine motion segments in the process of lifting. Large intersegmental changes may lead to higher demands of passive structures of the spine. Due to creep of ligaments and discs also in low loading situations frequent or long-time bending of motion-segments may be critically. In preventive context the squat-lifting-technique with reduced intersegmental motions is to prefer while frequent or heavy lifting. 5427 Tu, 16:30-16:45 (P24) A method o f evaluating the kinematics o f a spine deformed by scoliosis using a motion capture system P. Maciejasz 1, W. Chwafa 2. 1Institute of Precision and Biomedical Engineering, Warsaw University of Technology, Warsaw, Poland, 2Department of Anthropomotorics, Academy of Physical Education, Cracow, Poland Motion capture systems are being more commonly used to evaluate the kinematics of particular parts of the human body. Evaluating the kinematics of a spine using a motion capture system is very difficult because of the spine's movement under the skin. This problem becomes even more complicated when the spine is deformed, for example by scoliosis. If a method of evaluating the kinematics of a spine using a motion capture system is established, it would be very helpful when assessing the influence of certain exercises on the kinematics of a spine. An attempt has been made to establish a method which will enable us to evaluate the kinematics of a spine deformed by scoliosis. The method presented in this paper uses a novel model which calculates the positions and orientations of all vertebrae during movement using the B6zier parametric curve function. The input data for the model is the trajectories of markers placed on the head, thorax and pelvis, as well as information about the scoliotic curvature. The trajectories of markers are collected by a motion capture system. The Cobbe angle and other characteristics of the scoliotic curvature are assessed from a standing radiograph of the whole spine, in the PA view. The model was verified by dynamic trials. Gaits of 13 juveniles with idiopathic scoliosis were collected by the Vicon 250 Motion Capture System. The peak magnitude of the scoliotic curvature angle for all examined juveniles occurs at the same per cent of the gait cycle. In addition it has been observed that if there are two scoliotic curves, then the decrease in magnitude of one of them instantaneously increases the magnitude of the second one. The analysis also proves that the range of a lumbar spine's deformation magnitude is wider then that of a thoracic spine's. The method introduced in this paper shows good ability for scoliosis imaging during dynamic trials. When verified it may become a valuable tool for physiotherapists. 7332 Tu, 16:45-17:00 (P24) Assessment of soft tissue artifacts for flexion/extension movements o f the lumbar spine G.L. Ciavarro, G.C. Santambrogio, G. Andreoni. Dipartimente di
Bioingegneria, Politecnico di Milano, Milano, Italy Surface motion systems are widely applied to assess human mobility: despite their easy use derived from the adoption of passive skin markers, the
Journal o f Biomechanics 2006, Vol. 39 (Suppl 1)
Twelve healthy subjects (HS) and sixteen stroke patients presenting with a stiff knee gait were recruited. Wext was computed from the 3D ground reaction forces (GRFs, 100 c.p.s.) on a force measuring treadmill (Dierick 2004). Numerical integrations of the 3D accelerations gave the 3D speeds and the vertical displacement of the COMb, allowing the computation of the kinetic energy (Ek) and the gravitational potential energy (Ep). Positive (Wk+, Wp+) and negative works (Wk-, Wp-) were respectively obtained by adding the increments and decrements on Ek and Ep curves. By adding Ek and Ep, the total mechanical energy (Eext) was obtained, allowing the computation of Wext+ and Wext-. When the pathological leg supported the body weight, Wext+ and Wext- were normal (respectively 0.03±0.02 and 0.07±0.04Jkg -1). When the healthy leg supported the body weight, Wext+ was greater in patients (0.11±0.08 Jkg -1 , p = 0.013) than in healthy subjects (0.03±0.03 Jkg -1 ). This increase was mainly explained by an increase of Wp+ (0.15±0.09 vs 0.07±0.04 Jkg -1, p=0.009). When the pathological leg was in front during the double support, Wextwas greater in patients (0.11 ±0.06 Jkg -1 , p = 0.013) than in healthy subjects (0.05±0.03 Jkg -1). This increase was mainly explained by a nearly significant increase of Wp- (0.13±0.07 vs 0.09±0.03 Jkg -1 , p =0.065). On one hand, Wext+ of patients was increased and mainly produced by healthy limb muscles, to raise the COM b and make the foot clearance easier. On the other hand, Wext- was increased to absorb energy during the double support. The study of positive and negative works should improve our knowledge of the pathological gait mechanics.
5.13. Spine Kinematics 4039 Tu, 16:00-16:15 (P24) The effect o f small changes o f seat-back inclination on spine kinematics S. Adler, N. Piehler, J. H~nniger, R. Blickhan. Chair ef Motion Science,
Institute of Sports Science, Friedrich-Schiller-University, Jena, Germany Introduction: The influence of seat-back inclination on spinal loading and muscular activity has been widely studied [Harrison, Harrison, et al., 1999). Most of the studies, however, assessed different inclinations separately with the test person having to leave the seat between trials. This study aims to describe the effect of small changes of seat-back inclination on spine kinematics while the subject remains seated. Methods: 19 healthy adults (12 male, 7 female, age: 25.1±3.4 years; height: 177.2±7.4 cm; weight: 69.8±10.1 kg) were investigated during a 30 minute simulated driving test. Upper body movement and contact pressure were recorded. Seat-back inclination was varied every five minutes (18, 21, 24, 21, 18 degrees). [RB1] Results: (1) Posture and contact pressure show a high correlation. A reduction of lumbar lordosis and thoracic kyphosis results in an increased contact pressure at the back-rest and vice versa. Pressure under the ischial tuberosities is inversely related to the sum of back-rest pressure. (2) Posture and pressure readings change with altered seat-back inclination, but changes do not correlate with seat-back inclination. Head posture is unaffected by inclination changes. Discussion: (1) Because of the close relationship between posture and contact pressure, postural adaptations can be evaluated using continuous pressure measurement. Pressure under the ischial tuberosities is posture independent but is inversely related to the sum of back-rest pressure. This information helps to optimize the design of backrests to minimize ischemia of buttock tissue. (2) Posture is different for comparable seat-back inclinations, since posture and pressure readings differ significantly. Presumably, the fixed contact point of the ischial tuberosities and the initial pelvic angle, which are altered in recent studies due to repositioning of the subject between trials, are the main reasons for the observed kinematics. Conclusion: Spinal alignment and kinematics can not only be explained by seat-back angle. Current models must be modified to adequately describe spine kinematics for seated subjects. References Harrison D.D., Harrison S.O., et al. (1999). Sitting biomechanics part I: review of the literature. J Manipulative Physiol Ther, 1999; 22(9): 594~09.
Oral Presentations 4334 Tu, 16:15-16:30 (P24) Differences in lumbar spine motion pattern of weight-lifters and normal subjects performing freestyle lifting trials E MSrl 1, I. Bradl 2,3, R. Blickhan 4. 1Forschungsgesellschaft fEtr
angewandte Systemsicherheit und Arbeitsmedizin mbH, Erfurt, Germany, 2Berufsgenossenschaft Nahrungmittel und Gastst~tten, Prevention, Preventive Biomechanik, Erfurt, Germany, 3Friedrich-Schiller-University Jena, Clinic for accident surgery, motor research group, Jena, Germany, 4Friedrich-Schiller-University Jena, Institute of sport science, motion science, Jena, Germany Data of detailed intersegmental motion of the lumbar spine in daily-life-activities is rare. Most studies are in vitro or took under hardly restricted laboratoryconditions (X-ray or MRI). The aim of our study was to measure intersegmental lumbar spine motion patterns while lifting and compare motion strategies of different groups of subjects. The validity of the used method was analyzed by open MRI and rated as good. 11 subjects and 10 weight-lifters had to lift boxes choosing their favorite lifting technique. Box weight was random up to 15 kg for subjects and up to 60 kg for weight-lifters. Motion of lumbar spine was measured using infrared-light-based motion capturing and a skin-marker-method. Co-ordinates were transformed to 3-D Cardan-angles. In different lifting techniques (squat/stoop) different lumbar motion pattern were found: In squat-lifting (4 subjects) small range-of-motion on all lumbar levels were observed. In stoop-lifting (4 subjects) range-of-motion of motion segments is at average 3.25 times larger. 3 subjects performed a mixturetechnique. 9 out of 10 weight-lifters performed a squat-lifting-technique using also small range-of-motion. Spatial co-ordination of motion segments differs between this groups. Here the squat-lifters perform phases of very small motions of lumbar spine motion segments in the process of lifting. Large intersegmental changes may lead to higher demands of passive structures of the spine. Due to creep of ligaments and discs also in low loading situations frequent or long-time bending of motion-segments may be critically. In preventive context the squat-lifting-technique with reduced intersegmental motions is to prefer while frequent or heavy lifting. 5427 Tu, 16:30-16:45 (P24) A method o f evaluating the kinematics o f a spine deformed by scoliosis using a motion capture system P. Maciejasz 1, W. Chwafa 2. 1Institute of Precision and Biomedical Engineering, Warsaw University of Technology, Warsaw, Poland, 2Department of Anthropomotorics, Academy of Physical Education, Cracow, Poland Motion capture systems are being more commonly used to evaluate the kinematics of particular parts of the human body. Evaluating the kinematics of a spine using a motion capture system is very difficult because of the spine's movement under the skin. This problem becomes even more complicated when the spine is deformed, for example by scoliosis. If a method of evaluating the kinematics of a spine using a motion capture system is established, it would be very helpful when assessing the influence of certain exercises on the kinematics of a spine. An attempt has been made to establish a method which will enable us to evaluate the kinematics of a spine deformed by scoliosis. The method presented in this paper uses a novel model which calculates the positions and orientations of all vertebrae during movement using the B6zier parametric curve function. The input data for the model is the trajectories of markers placed on the head, thorax and pelvis, as well as information about the scoliotic curvature. The trajectories of markers are collected by a motion capture system. The Cobbe angle and other characteristics of the scoliotic curvature are assessed from a standing radiograph of the whole spine, in the PA view. The model was verified by dynamic trials. Gaits of 13 juveniles with idiopathic scoliosis were collected by the Vicon 250 Motion Capture System. The peak magnitude of the scoliotic curvature angle for all examined juveniles occurs at the same per cent of the gait cycle. In addition it has been observed that if there are two scoliotic curves, then the decrease in magnitude of one of them instantaneously increases the magnitude of the second one. The analysis also proves that the range of a lumbar spine's deformation magnitude is wider then that of a thoracic spine's. The method introduced in this paper shows good ability for scoliosis imaging during dynamic trials. When verified it may become a valuable tool for physiotherapists. 7332 Tu, 16:45-17:00 (P24) Assessment of soft tissue artifacts for flexion/extension movements o f the lumbar spine G.L. Ciavarro, G.C. Santambrogio, G. Andreoni. Dipartimente di
Bioingegneria, Politecnico di Milano, Milano, Italy Surface motion systems are widely applied to assess human mobility: despite their easy use derived from the adoption of passive skin markers, the