***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: Study Design . Three factors mixed- design with 1 between-subject and 2 within-subject factors . Objective . To compare the main effects and interactions of postural and cognitive difficulty on quiet stance between subjects with and without nonspecific low back pain ( LBP ) . Summary of Background Data . The interference between postural control and cognitive tasks depends on factors such as sensorimotor/cognitive integrity . Changes in peripheral sensory and muscular systems as well as cognitive processes have been observed in LBP patients . It was hypothesized that the effect of cognitive task on postural performance might be different in subjects with nonspecific LBP as compared with healthy individuals . To the authors ’ knowledge this has not been investigated before . Methods . Postural stability was measured by center of pressure parameters while nonspecific LBP ( n = 22 ) and healthy ( n = 22 ) subjects r and omly performed quiet st and ing task with 3 levels of difficulty ( rigid-surface eyes open , rigid-surface eyes-closed , and foam-surface eyes-closed ) in isolation or concurrently with an easy or difficult digits backward cognitive task . Results . Subjects with nonspecific LBP had less postural sway than healthy subjects , while postural sway decreased with increase in the level of cognitive difficulty . Nonspecific LBP and healthy subjects had larger postural sway at more difficult sensory conditions such as rigid-surface eyes-closed and foam-surface eyes-closed . The response to dual-tasking was not significantly different between the 2 groups . Conclusion . The dual-tasking did not change the postural performance of nonspecific LBP subjects with low level of pain and disability differently compared to healthy subjects This study evaluated the degree to which the disturbance to posture from respiration is compensated for in healthy normals and whether this is different in people with recurrent low back pain ( LBP ) , and to compare the changes when respiratory dem and is increased . Angular displacement of the lumbar spine and hips , and motion of the centre of pressure ( COP ) , were recorded with high resolution and respiratory phase was recorded from ribcage motion . With subjects st and ing in a relaxed posture , recordings were made during quiet breathing , while breathing with increased dead-space to induce hypercapnoea , and while subjects voluntarily increased their respiration to match ribcage expansion that was induced in the hypercapnoea condition . The relationship between respiration and the movement parameters was measured from the coherence between breathing and COP and angular motion at the frequency of respiration , and from averages triggered from the respiratory data . Small angular changes in the lumbopelvic and hip angles were evident at the frequency of respiration in both groups . However , in quiet st and ing , the LBP subjects had a greater displacement of their COP that was associated with respiration than the control subjects . The LBP group had a trend for less hip motion . There were no changes in the movement parameters when respiratory dem and increased involuntarily via hypercapnoea , but when respiration increased voluntarily , the amplitude of motion and the displacement of the COP increased in both groups . The present data suggest that the postural compensation to respiration counteracts at least part of the disturbance to posture caused by respiration and that this compensation may be less effective in people with LBP Tonic muscle nociceptive discharge evoked chemically from the foot extensor digitorum brevis muscle in man produces a depression of Ia excitation and Ib inhibition of the soleus ( Sol ) motoneurones ( Mns ) . The possibility that both these changes partly result from presynaptic inhibition of Ia fibres projecting to Sol Mns and to interneurones mediating group I non-reciprocal inhibition is tested . Convergence of Ia fibres on these interneurones was deduced from evidence that reducing the excitatory effect of the extensor Ia fibres ( by potentiation of their presynaptic inhibition ) result ed in Ib disinhibition . Nociceptive-induced potentiation of Ia presynaptic inhibition was deduced from the following congruent results obtained by two independent methods : ( 1 ) depression of heteronymous Ia monosynaptic facilitation of the quadriceps muscle to Sol Mns ; ( 2 ) potentiation of presynaptic inhibition of Sol Ia fibres evoked by mechanical activation of the tibialis anterior primary spindle afferents . It is concluded that nociceptive volleys arising from dorsal foot muscles facilitate the activity of interneurones intercalated in pathways responsible for presynaptic inhibition of Sol Ia fibres . It is also proposed that the same Ia presynaptic inhibition depresses the excitability of interneurones mediating group I non-reciprocal inhibition , thus result ing in Ib disinhibition of Sol Mns Objectives : To describe postural sway and its associations to background factors , low back pain and functional capacity . To evaluate the changes in postural sway after three months of therapeutic exercise in the gym or at home . Design : A one-year r and omized experimental trial evaluated postural sway in three study groups : intensive training , home exercise and control group . Setting : Subjects were recruited from seven local occupational health care centres in Central Finl and and were examined at Central Finl and Hospital by medical doctors .  Measurements and therapeutic exercise programmes were carried out in the Research Laboratory of Sport and Health Sciences at Jyväskylä University . Subjects : Initially , 49 male and 41 female subjects ( aged 20–55 years ) with nonspecific and subacute low back pain were examined . Main outcome measures : Postural sway using a force platform , the Oswestry Index , as well as a measure of low back pain intensity were measured at the initial stage of the study , directly after interventions , as well as at three and nine months after the interventions . Results : The background variables were not strongly correlated with postural sway . No changes occurred in the amplitude of sway during the study , but the sway velocity of the home exercise group increased . Conclusions : Postural sway measurements with a force platform may be suitable for detecting impairments of balance performance among subjects with pronounced functional or activity limitations and severe low back pain problems . In order to enhance balance performance , specific and customized exercise programmes are required 1 . We studied  quiet stance  investigating strategies for maintaining balance .  Normal subjects stood with natural stance and with feet together  , with eyes open or closed . Kinematic , kinetic and EMG data were evaluated and cross-correlated . 2 . Cross-correlation analysis revealed a high , positive , zero-phased correlation between anteroposterior motions of the centre of gravity ( COG ) and centre of pressure ( COP ) , head and COG , and between linear motions of the shoulder and knee in both sagittal and frontal planes . There was a moderate , negative , zero-phased correlation between the anteroposterior motion of COP and ankle angular motion . 3 . Narrow stance width increased ankle angular motion , hip angular motion , mediolateral sway of the COG , and the correlation between linear motions of the shoulder and knee in the frontal plane . Correlations between COG and COP and linear motions of the shoulder and knee in the sagittal plane were decreased . The correlation between the hip angular sway in the sagittal and frontal planes was dependent on interaction between support and vision . 4 . Low , significant positive correlations with time lags of the maximum of cross-correlation of 250 - 300 ms were found between the EMG activity of the lateral gastrocnemius muscle and anteroposterior motions of the COG and COP during normal stance . Narrow stance width decreased both correlations whereas absence of vision increased the correlation with COP . 5 . Ankle mechanisms dominate during normal stance especially in the sagittal plane . Narrow stance width decreased the role of the ankle and increased the role of hip mechanisms in the sagittal plane , while in the frontal plane both increased . 6 . The modulation pattern of the lateral gastrocnemius muscle suggests a central program of control of the ankle joint stiffness working to predict the loading pattern OBJECTIVE To determine whether body balance is perturbed more in low back pain patients than in healthy subjects , under the concept of posturo-kinetic capacity . DESIGN Comparison of posturographic and respiratory parameters between low back pain and healthy subjects . BACKGROUND It has been demonstrated that respiratory movements constitute a perturbation to posture , compensated by movements of the spine and of the hips , and that low back pain is frequently associated with a loss of back mobility . METHOD Ten low back pain patients and ten healthy subjects performed five posturographic tests under three different respiratory rate conditions : quiet breathing ( spontaneous ) , slow breathing ( 0.1 Hz ) and fast breathing ( 0.5 Hz ) . RESULTS Intergroup comparison showed that the mean displacements of the center of pressure were greater for the low back pain group , especially along the antero-posterior axis , where respiratory perturbation is primarily exerted . Inter-condition comparison showed that in slow and fast breathing relatively to quiet breathing , the mean displacement of the center of pressure along the antero-posterior axis was significantly increased only for the low back pain group . CONCLUSION According to the results , respiration presented a greater disturbing effect on body balance in low back pain subjects . RELEVANCE This study provides information on the causes of the impaired body balance associated with chronic low back pain , which could be used to improve treatment strategy In this study , we describe a device for the direct measurement of intrinsic ankle stiffness in quiet st and ing . It consists of a motorised footplate mounted on a force platform . By generating r and om sequences of step-like disturbances ( 1 degrees amplitude , 150 ms duration ) and measuring the corresponding displacements of the center of pressure in the antero-posterior direction , we obtained torque-rotation patterns after aligning , averaging , and scaling the postural responses . Such patterns were used for estimating the value of the ankle stiffness , which was normalized as a fraction of the critical value . In order to be confident that the measurements addressed the intrinsic ankle stiffness and were not affected in a significant way by the reflex activation of the muscles in response to the test disturbances , we performed the estimates in different ways : least squares estimates with time windows of different widths and an instantaneous estimate at the time in which the angular acceleration vanishes . The statistical analysis showed that there is no significant difference among the different methods of estimate and the inspection of the electromyographic activity in response to the perturbations showed that at least two of the estimates were certainly outside the possible influence of reflex patterns . The intrinsic ankle stiffness was evaluated to be 64+/-8 % of the critical stiffness for test disturbances of the order of 1 degrees . We argue that this figure identifies the lower bound of the range of values which characterise normal sway in quiet st and ing , whereas the upper bound is given by the estimates performed with much smaller test disturbances [ 1 ] which yield a higher value : 91+/-23 % . The two estimation paradigms ( with very small and very large test disturbances , respectively ) are complementary also because they behave in a different way as regards the sensitivity to a bias torque : it is close to zero in the Loram & Lakie 's paradigm , whereas it is significant in our paradigm . Thus , as the bias grows , it appears that the range of stiffness values is narrowed and is pushed towards the upper bound . There is a clear potential for the clinical application of these methods , in the sense that the identification of the range of stiffness values used by a patient is a measurable index of motor organisation/reorganisation Insight into the mechanisms of altered postural control in persons with low back pain ( LBP ) could lead to better interventions for patients with LBP . This study investigated ( 1 ) whether persons with recurrent LBP have an altered body inclination , and ( 2 ) whether anticipation of postural instability further alters body inclination . Thirty-three young healthy individuals and 56 young persons with recurrent LBP participated in this study .  The upright st and ing posture was evaluated by means of two piezo-resistive electrogoniometers and a force platform for the conditions as follows : ( 1 ) quiet stance with and without vision , and ( 2 ) in anticipation of postural instability due to a ballistic arm movement or ankle muscle vibration . No differences in body inclination were observed when visual information was available between the two groups ( P>0.05 ) . However , significant more forward inclination was seen in the persons with recurrent LBP when vision was occluded ( + 7.4 % ) and in anticipation of postural instability ( + 19 % ) ( P<0.05 ) compared to the healthy individuals . The results suggest that young persons with recurrent LBP have an altered body inclination that might be caused by anticipation of postural instability . The adopted forward inclined posture may potentially be a factor in the recurrence of LBP Abstract : To determine whether the presence of back pain and its related disabilities are determinants of balance and functional mobility in a group of women with osteoporosis , we carried out a cross-sectional analysis of 93 community-dwelling women with osteoporosis between the ages of 65 and 75 years old . We assessed health history , anthropometrics , self-report of current physical activity level and self-report of back pain ( intensity and pain-related disabilities ) . Balance  was measured by computerized dynamic posturography and functional mobility was assessed by timed figure-of-eight test .  The prevalence of back pain was high ( 75 % ) in this cohort of older women with osteoporosis . Age was the major determinant of both balance and functional mobility and accounted for 9 % and 14 % of the variance , respectively . After accounting for age , back pain explained an additional 9 % of the variance in balance and 13 % of the variance in functional mobility . The high prevalence of back pain demonstrates the importance of pain management in the treatment of osteoporosis . Furthermore , the finding of self-reported back pain as a determinant of both balance and functional mobility suggests that this measure may deserve attention when screening women with osteoporosis for fracture risk . Prospect i ve studies are needed to determine whether pain management will improve balance and functional mobility Study Design . A follow-up study evaluating postural control , lumbar movement perception , and paraspinal muscle reflexes in disc herni 
    Output:
    
Patients with NSLBP exhibit greater postural instability than healthy controls , signified by greater COP excursions and a higher mean velocity .
While the decreased postural stability in NSLBP sufferers further appears to be associated with the presence of pain , it seems unrelated to the exact location and pain duration .
No correlation between the pain intensity and the magnitude of COP excursions could be identified