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Abdominal muscles contribute in a minor way to peak spinal compression in lifting
374
Journal of Manipulative and Physiological Therapeutics Volume 23 ° Number 5 • June 2000
Journal Abstracts
Results: Borg scale ratings correlated with endurance time (0.68) and EMG median- and mean power frequency slopes (0.41-0.50). At a Borg rating of 3, median- and mean power frequency and endurance time were reduced by 30%. At a Borg rating of 5, median- and mean power frequency and endurance time were reduced by 50%. At a Borg rating of 7, median- and mean power frequency and endurance time were reduced by 60-70%. Conclusions: Significant correlation between the Borg scale, EMG and endurance time suggests a close relationship between subjective and objective assessment of muscle fatigue. Relevance: The close relationship between EMG, endurance time and the Borg scale, is proposed to be useful in clinical testing. A sub-maximal time performance until a Borg rating of 5 (strong fatigue) is reached could be preferred to limit the factor of motivation in a testing situation. Reprinted from Clinical Biomechanics, Volume 14, Dedering/~, N6meth G, Harms-Ringdahl K, Correlation between electromyographic spectral changes and subjective assessment of lumbar muscle fatigue in subjects without pain from the lower back, 103-11, 1999, with permisson from Elsevier Science Ltd.
de Looze MP, Groen H, Horemans H, Kingma I, van Die~n JH. Abdominal musclescontribute in a minorway to peak spinal compression in lifting. J Biomech 1999;32:655-62.
ABSTRACT: In lifting, the abdominal muscles are thought to be activated to stabilize the spine. As a detrimental effect, they contribute to spinal compression. The existing literature is not conclusive about the biological relevance of this effect. From biological, mechanical and anatomical considerations it was hypothesized that the relative abdominal contribution to compression would be minor in the beginning of the lift, that the relative and absolute abdominal contribution to compression would rise throughout the lift, and that the obliques would contribute to a larger extent than the rectus abdominis. To investigate these hypotheses, 10 subjects lifted 0.5, 10.5 and 22.5 kg. EMG levels obtained from the rectus abdominis and the obliques were converted into force using normalized EMG, muscle potential and area values, and modulating factors for muscle length and contraction velocity. An anatomical model was applied to compute the abdominal effects on spinal compression in three consecutive phases within a lift. If expressed relative to the total spinal compression, the abdominai contribution for the three weight conditions was 7.1% (SD, 1.7), 10.4% (4.7) and 12.5% (4.4) in the beginning and 21,0% (5.8), 19.0% (5.3) and 22.2% (6.6) in the end phase. Thus, the relative abdominal contribution to compression was minor in the beginning and increased towards the end. The absolute abdominal contribution was constant throughout the lift. The contributions could be retraced to the obliques rather than the rectus, while during the lift a shift in activation from the obfiquus externus to internus was observed. Reprinted from the Journal of Biomechanics, Volume
32, de Looze ME Groen H, Horemans H, Kingma I, van DieEn JH, Abdominal muscles contribute in a minor way to peak spinal compression in lifting, 655-62, 1999, with permisson from Elsevier Science Ltd.
EngstromT, Hanse JJ, Kadefors R. Musculoskeletalsymptomsdue to technical preconditions in longcycle time work in an automobileassembly plant: a study of prevalenceand relation to psychologicalfactors and physical exposure.Appl Ergon 1999;30:443-53. ABSTRACT: The aim was to evaluate the prevailing ergonomic conditions in a parallelized flow, long cycle time, assembly system. The evaluation focused on physical exposure, psychosocial factors and work-related musculoskeletal symptoms. A random sample of 67 assembly operators was included in a cross-sectional study mainly based on questionnaires. Hand/ wrist symptoms were common and related to work exposure with hand-held powered tools. In general, the self-reported physical exposure showed only a few significant associations with musculoskeletal symptoms. This may in part be explained by the ergonomic conditions generally being good, with a relatively low duration of 'combined' extreme work postures. Significant associations were found between the psychosocial work environment and musculoskeletal symptoms. Reprinted from Applied Ergonomics, Volume 30, Engstrom T, Hanse J J, Kadefors R, Musculoskeletal symptoms due to technical preconditions in long cycle time work in an automobile assembly plant: a study of prevalence and relation to psychological factors and physical exposure, 44353, 1999, with permission from Elsevier Science Ltd.
Gu M, Leung Lai T. Determinationof power and sample size in the design of clinical trials with failure-timeendpoints and interim analyses. Control Clin Trials 1999;20:423-38.
ABSTRACT: An important but difficult task in the design of a clinical trial to compare time to failure between two treatment groups is determination of the number of patients required to achieve a specified power of the test. Because patients typically enter the trial serially and are followed until they fail or withdraw from the study or until the study is terminated, the power of the test depends on the accrual pattern, the noncompliance rate, and the withdrawal rate in addition to the actual survival distributions of the two groups. Incorporating interim analyses and the possibility of early stopping into the trial increases its complexity, and although normal approximations have been developed for computing the significance level of the test when the log-rank or other rank statistics are used, there are no reliable analytic approximations for evaluating the power of the test. This article presents methods, based on Monte Carlo simulations and recent advances in group sequential testing with time-to-event responses, to choose appropriate test statistics, compute power and sample size at specified alternatives, cheek the adequacy of commonly used"
Journal of Manipulative and Physiological Therapeutics Volume 23 ° Number 5 • June 2000
Journal Abstracts
Results: Borg scale ratings correlated with endurance time (0.68) and EMG median- and mean power frequency slopes (0.41-0.50). At a Borg rating of 3, median- and mean power frequency and endurance time were reduced by 30%. At a Borg rating of 5, median- and mean power frequency and endurance time were reduced by 50%. At a Borg rating of 7, median- and mean power frequency and endurance time were reduced by 60-70%. Conclusions: Significant correlation between the Borg scale, EMG and endurance time suggests a close relationship between subjective and objective assessment of muscle fatigue. Relevance: The close relationship between EMG, endurance time and the Borg scale, is proposed to be useful in clinical testing. A sub-maximal time performance until a Borg rating of 5 (strong fatigue) is reached could be preferred to limit the factor of motivation in a testing situation. Reprinted from Clinical Biomechanics, Volume 14, Dedering/~, N6meth G, Harms-Ringdahl K, Correlation between electromyographic spectral changes and subjective assessment of lumbar muscle fatigue in subjects without pain from the lower back, 103-11, 1999, with permisson from Elsevier Science Ltd.
de Looze MP, Groen H, Horemans H, Kingma I, van Die~n JH. Abdominal musclescontribute in a minorway to peak spinal compression in lifting. J Biomech 1999;32:655-62.
ABSTRACT: In lifting, the abdominal muscles are thought to be activated to stabilize the spine. As a detrimental effect, they contribute to spinal compression. The existing literature is not conclusive about the biological relevance of this effect. From biological, mechanical and anatomical considerations it was hypothesized that the relative abdominal contribution to compression would be minor in the beginning of the lift, that the relative and absolute abdominal contribution to compression would rise throughout the lift, and that the obliques would contribute to a larger extent than the rectus abdominis. To investigate these hypotheses, 10 subjects lifted 0.5, 10.5 and 22.5 kg. EMG levels obtained from the rectus abdominis and the obliques were converted into force using normalized EMG, muscle potential and area values, and modulating factors for muscle length and contraction velocity. An anatomical model was applied to compute the abdominal effects on spinal compression in three consecutive phases within a lift. If expressed relative to the total spinal compression, the abdominai contribution for the three weight conditions was 7.1% (SD, 1.7), 10.4% (4.7) and 12.5% (4.4) in the beginning and 21,0% (5.8), 19.0% (5.3) and 22.2% (6.6) in the end phase. Thus, the relative abdominal contribution to compression was minor in the beginning and increased towards the end. The absolute abdominal contribution was constant throughout the lift. The contributions could be retraced to the obliques rather than the rectus, while during the lift a shift in activation from the obfiquus externus to internus was observed. Reprinted from the Journal of Biomechanics, Volume
32, de Looze ME Groen H, Horemans H, Kingma I, van DieEn JH, Abdominal muscles contribute in a minor way to peak spinal compression in lifting, 655-62, 1999, with permisson from Elsevier Science Ltd.
EngstromT, Hanse JJ, Kadefors R. Musculoskeletalsymptomsdue to technical preconditions in longcycle time work in an automobileassembly plant: a study of prevalenceand relation to psychologicalfactors and physical exposure.Appl Ergon 1999;30:443-53. ABSTRACT: The aim was to evaluate the prevailing ergonomic conditions in a parallelized flow, long cycle time, assembly system. The evaluation focused on physical exposure, psychosocial factors and work-related musculoskeletal symptoms. A random sample of 67 assembly operators was included in a cross-sectional study mainly based on questionnaires. Hand/ wrist symptoms were common and related to work exposure with hand-held powered tools. In general, the self-reported physical exposure showed only a few significant associations with musculoskeletal symptoms. This may in part be explained by the ergonomic conditions generally being good, with a relatively low duration of 'combined' extreme work postures. Significant associations were found between the psychosocial work environment and musculoskeletal symptoms. Reprinted from Applied Ergonomics, Volume 30, Engstrom T, Hanse J J, Kadefors R, Musculoskeletal symptoms due to technical preconditions in long cycle time work in an automobile assembly plant: a study of prevalence and relation to psychological factors and physical exposure, 44353, 1999, with permission from Elsevier Science Ltd.
Gu M, Leung Lai T. Determinationof power and sample size in the design of clinical trials with failure-timeendpoints and interim analyses. Control Clin Trials 1999;20:423-38.
ABSTRACT: An important but difficult task in the design of a clinical trial to compare time to failure between two treatment groups is determination of the number of patients required to achieve a specified power of the test. Because patients typically enter the trial serially and are followed until they fail or withdraw from the study or until the study is terminated, the power of the test depends on the accrual pattern, the noncompliance rate, and the withdrawal rate in addition to the actual survival distributions of the two groups. Incorporating interim analyses and the possibility of early stopping into the trial increases its complexity, and although normal approximations have been developed for computing the significance level of the test when the log-rank or other rank statistics are used, there are no reliable analytic approximations for evaluating the power of the test. This article presents methods, based on Monte Carlo simulations and recent advances in group sequential testing with time-to-event responses, to choose appropriate test statistics, compute power and sample size at specified alternatives, cheek the adequacy of commonly used"