***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Little consensus exists in the literature regarding methods for determination of the onset of electromyographic ( EMG ) activity . The aim of this study was to compare the relative accuracy of a range of computer-based techniques with respect to EMG onset determined visually by an experienced examiner . Twenty-seven methods were compared which varied in terms of EMG processing ( low pass filtering at 10 , 50 and 500 Hz ) , threshold value ( 1 , 2 and 3 SD beyond mean of baseline activity ) and the number of sample s for which the mean must exceed the defined threshold ( 20 , 50 and 100 ms ) . Three hundred r and omly selected trials of a postural task were evaluated using each technique . The visual determination of EMG onset was found to be highly repeatable between days . Linear regression equations were calculated for the values selected by each computer method which indicated that the onset values selected by the majority of the parameter combinations deviated significantly from the visually derived onset values . Several methods accurately selected the time of onset of EMG activity and are recommended for future use This study investigated whether people with low back pain ( LBP ) reduce variability of movement between the pelvis and thorax ( trunk ) in the transverse plane during gait at different speeds compared to healthy controls . Thirteen people with chronic LBP and twelve healthy controls  walked on a treadmill  at speeds from 0.5 to 1.72 m/s , with increments of 0.11 m/s . Step-to-step variability of the trunk , pelvis , and thorax rotations were calculated . Step-to-step deviations of pelvis and thorax rotations from the average pattern ( residual rotations ) were correlated to each other , and the linear regression coefficients between these deviations calculated . Spectral analysis was used to determine the frequencies of the residual rotations , to infer the relation of reduced trunk variability to trunk stiffness and /or damping . Variability of trunk motion ( thorax relative to pelvis ) was lower ( P=0.02 ) , covariance between the residual rotations of pelvis and thorax motions was higher ( P=0.03 ) , and the linear regression coefficients were closer to 1 ( P=0.05 ) in the LBP group . Most power of segmental residual rotations was below stride frequency ( ~1 Hz ) . In this frequency range , trunk residual rotations had less power than pelvis or thorax residual rotations . These data show that people with LBP had lower variability of trunk rotations , as a result of the coupling of deviations of residual rotations in one segment to deviations of a similar shape ( correlation ) and amplitude ( regression coefficient ) in the other segment . These results support the argument that people with LBP adopt a protective movement strategy , possibly by increased trunk stiffness BACKGROUND Static trunk flexion working postures and disturbed trunk muscle reflexes are related to increased risk of low-back pain .  Animal studies conclude that these factors may be related ; passive tissue strain in spinal ligaments causes subsequent short-term changes in reflex . Although studies have documented changes in the myoelectric onset angle of flexion-relaxation following prolonged static flexion and cyclic flexion we could find no published evidence related to the human reflex response of the trunk extensor muscles following a period of static flexion-relaxation loading . METHODS Eighteen subjects  maintained static lumbar flexion for 15 min . Paraspinal muscle reflexes were elicited both before and after the flexion-relaxation protocol using pseudor and om stochastic force disturbances while recording EMG .  Reflex gain was computed from the peak value of the impulse response function relating input force perturbation to EMG response using time-domain deconvolution analyses . FINDINGS Reflexes showed a trend toward increased gain after the period of flexion-relaxation ( P < 0.055 ) and were increased with trunk extension exertion ( P < 0.021 ) . Significant gender differences in reflex gain were observed ( P < 0.01 ) . INTERPRETATIONS Occupational activities requiring extended periods of trunk flexion contribute to changes in reflex behavior of the paraspinal muscles . Results suggest potential mechanisms by which flexed posture work may contribute to low-back pain . Significant gender differences indicate risk analyses should consider personal factors when considering neuromuscular behavior Spinal stability is related to both the intrinsic stiffness of active muscle as well as neuromuscular reflex response . However , existing analyses of spinal stability ignore the role of the reflex response , focusing solely on the intrinsic muscle stiffness associated with voluntary activation patterns in the torso musculature . The goal of this study was to empirically characterize the role of reflex components of spinal stability during voluntary trunk extension exertions . Pseudor and om position perturbations of the torso and associated driving forces were recorded in 11 healthy adults . Nonlinear systems- identification analyses of the measured data provided an estimate of total systems dynamics that explained 81 % of the movement variability . Proportional intrinsic response was less than zero in more than 60 % of the trials , e.g. mean value of P(INT ) during the 20 % maximum voluntary exertion trunk extension exertions -415+/-354N/m . The negative value indicated that the intrinsic muscle stiffness was not sufficient to stabilize the spine without reflex response . Reflexes accounted for 42 % of the total stabilizing trunk stiffness . Both intrinsic and reflex components of stiffness increased significantly with trunk extension effort . Results reveal that reflex dynamics are a necessary component in the stabilizing control of spinal stability Study Design . Transverse pelvis and thorax rotations were studied during walking in 39 patients with nonspecific low back pain and 19 healthy participants . Objectives . To gain insight into the consequences of low back pain for gait and to identify clinical ly useful measures for characterizing the quality of walking in patients with low back pain . Summary of Background Data . Gait studies in patients with low back pain have reported a decrease in walking velocity . In normal gait , in-phase pelvis-thorax coordination ( synchronicity ) evolves toward antiphase coordination ( counterrotation ) as walking velocity increases . This study examined the effect of walking velocity on  pelvis and thorax rotations  in patients with low back pain . Methods .  Amplitudes of pelvis and thorax rotations  were calculated , and spectral analyses were performed . Pelvis-thorax coordination was characterized in terms of relative Fourier phase , and coupling strength was assessed by means of cross-spectral analysis . Results . In comparison with healthy participants , relative Fourier phase was significantly smaller in low back pain patients for walking velocities of 3.8 km/h and higher , whereas coupling strength was significantly higher for velocities from 1.4 to 3.0 km/h . No significant group differences were found in amplitude or spectral content of individual pelvis and thorax rotations . Conclusion . In comparison with healthy participants , the gait of patients with low back pain was characterized by a more rigid , less flexible pelvis-thorax coordination in the absence of significant differences in the kinematics of the component rotations . This result suggests that coordination measures are more adequate in assessing quality of walking in patients with low back pain than are kinematic measures pertaining to the individual segment rotations , and that conservative therapy should use methods aim ed at improving intersegmental coordination A false positive is the mistake of inferring an effect when none exists , and although α controls the false positive ( Type I error ) rate in classical hypothesis testing , a given α value is accurate only if the underlying model of r and omness appropriately reflects experimentally observed variance . Hypotheses pertaining to one-dimensional ( 1D ) ( e.g. time-varying ) biomechanical trajectories are most often tested using a traditional zero-dimensional ( 0D ) Gaussian model of r and omness , but variance in these data sets is clearly 1D . The purpose of this study was to determine the likelihood that analyzing smooth 1D data with a 0D model of variance will produce false positives . We first used r and om field theory ( RFT ) to predict the probability of false positives in 0D analyses . We then vali date d RFT predictions via numerical simulations of smooth Gaussian 1D trajectories . Results showed that , across a range of public kinematic , force/moment and EMG data sets , the median false positive rate was 0.382 and not the assumed α=0.05 , even for a simple two- sample t test involving N=10 trajectories per group . The median false positive rate for experiments involving three-component vector trajectories was p=0.764 . This rate increased to p=0.945 for two three-component vector trajectories , and to p=0.999 for six three-component vectors . This implies that experiments involving vector trajectories have a high probability of yielding 0D statistical significance when there is , in fact , no 1D effect . Either ( a ) explicit a priori identification of 0D variables or ( b ) adoption of 1D methods can more tightly control α Study Design . A follow-up study evaluating postural control , lumbar movement perception , and paraspinal muscle reflexes in disc herniation-related chronic low back pain ( LBP ) before and after discectomy .  Objectives . To assess the effect of discectomy on postural control , lumbar perception , and reflex activation of paraspinal muscles during sudden upper limb loading . Summary of Background Data . Impaired muscle function , postural control , and lumbar proprioception have been observed in LBP . However , they have not been studied in sciatica patients after surgery . Methods . The study included 20 patients selected for an operation for chronic LBP caused by disc herniation and 15 controls without chronic LBP . The paraspinal muscle responses for upper limb loading during unexpected and expected conditions were measured by surface electromyography . The ability to sense lumbar rotation was assessed in a previously vali date d motorized trunk rotation unit in the seated position . The postural control was measured with a vertical force platform . Pain , disability , and depression scores were recorded . Results . Patients had poorer lumbar perception ( P = 0.012 ) and postural control ( P < 0.05 ) than did healthy controls . The postural control remained unchanged , but lumbar perception ( P = 0.054 ) and the lumbar feed-forward control ( P = 0.043 ) improved after the surgery . Conclusions . The results demonstrate impaired lumbar proprioception and postural control in sciatica patients . During short-term follow-up after operative treatment , postural control does not seem to change , but impaired lumbar proprioception and feed-forward control of paraspinal muscles seem to recover Study Design . Prospect i ve observational study with a 2- to 3-year follow-up . Objectives . To determine whether delayed muscle reflex response to sudden trunk loading is a result of or a risk factor for sustaining a low back injury ( LBI ) . Summary of Background Data . Differences in motor control have been identified in individuals with chronic low back pain and in athletes with a history of LBI when compared with controls . However , it is not known whether these changes are a risk for or a result of LBI . Methods .  Muscle reflex latencies  in response to a quick force release in trunk flexion , extension , and lateral bending were measured in 303 college athletes . Information was also obtained regarding their personal data , athletic experience , and history of LBI . The data were entered into a binary logistic regression model to identify the predictors of future LBI . Results . A total of 292 athletes were used for the final analysis ( 148 females and 144 males ) . During the follow-up period , 31 ( 11 % ) athletes sustained an LBI . The regression model , consisting of history of LBI , body weight , and the latency of muscles shutting off during flexion and lateral bending load releases , predicted correctly 74 % of LBI outcomes . The odds of sustaining LBI increased 2.8-fold when a history of LBI was present and increased by 3 % with each millisecond of abdominal muscle shut-off latency . On average , this latency was 14 milliseconds longer for athletes who sustained LBI in comparison to athletes who did not sustain LBI ( 77 [ 36 ] vs. 63 [ 31 ] ) . There were no significant changes in any of the muscle response latencies on retest following the injury . Conclusions . The delayed muscle reflex response significantly increases the odds of sustaining an LBI . These delayed latencies appear to be a preexisting risk factor and not the effect of an LBI OBJECTIVE To analyze muscle activation patterns during various footplate perturbations , used as proprioceptive challenges in patients with low back pain ( LBP ) and in controls . DESIGN A prospect i ve and controlled comparative study . SETTING Outpatient clinic . PARTICIPANTS Twenty subjects with chronic LBP and 20 age- and sex-matched controls . INTERVENTIONS The subjects underwent 5 sets of footplate perturbations in 3 directions with 16 perturbations for each set . MAIN OUTCOME MEASURES Latency , frequency , and asymmetry of muscle activation of the erector spinae , rectus abdominus , anterior tibialis , and gastrocnemius muscles were measured bilaterally with  surface electromyography .  RESULTS In the toes-up movements , subjects with LBP were significantly less likely to activate their rectus abdominus muscles ( P=.02 ) , and they were more likely to exhibit asymmetric muscle activation in the smaller forward movements ( odds ratio=4.1 , P=.03 ) . The latter result appears to be driven by asymmetric contraction of the erector spinae and rectus abdominus . CONCLUSIONS Significantly more subjects with LBP than control subjects exhibited absent firing of trunk muscles during 2 of the 5 footplate perturbations . These results suggest an abnormality of the neuromuscular loop and may represent altered proprioception When investigating the dynamics of three-dimensional multi-body biomechanical systems it is often difficult to derive spatiotemporally directed predictions regarding experimentally induced effects . A paradigm of ' non-directed ' hypothesis testing has emerged in the literature as a result . Non-directed analyses typically consist of ad hoc scalar extraction , an approach which substantially simplifies the original , highly multivariate data sets ( many time points , many vector components ) . This paper describes a commensurately multivariate method as an alternative to scalar extraction . The method 
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We found evidence of a longer response time of muscle activation , which would be in line with splinting behaviour in LBP .
No signs of splinting behaviour were found in any of the other outcome measures .
Conclusions We conclude that there is currently no convincing evidence for the presence of splinting behaviour in LBP patients , because we found no indications for splinting in terms of kinetic and kinematic responses to perturbation and derived mechanical properties of the trunk .
Consistent evidence on delayed onsets of muscle activation in response to perturbations was found , but this may have other causes than splinting behaviour