***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 . A r and omized clinical trial with 1-year and 3-year telephone question naire follow-ups . Objective . To report a specific exercise intervention ’s long-term effects on recurrence rates in acute , first-episode low back pain patients . Summary of Background Data . The pain and disability associated with an initial episode of acute low back pain ( LBP ) is known to resolve spontaneously in the short-term in the majority of cases . However , the recurrence rate is high , and recurrent disabling episodes remain one of the most costly problems in LBP . A deficit in the multifidus muscle has been identified in acute LBP patients , and does not resolve spontaneously on resolution of painful symptoms and resumption of normal activity . Any relation between this deficit and recurrence rate was investigated in the long-term . Methods . Thirty-nine patients with acute , first-episode LBP were medically managed and r and omly allocated to either a control group or specific exercise group . Medical management included advice and use of medications . Intervention consisted of exercises aim ed at rehabilitating the multifidus in cocontraction with the transversus abdominis muscle . One year and three years after treatment , telephone question naires were conducted with patients . Results . Question naire results revealed that patients from the specific exercise group experienced fewer recurrences of LBP than patients from the control group . One year after treatment , specific exercise group recurrence was 30 % , and control group recurrence was 84 % ( P < 0.001 ) . Two to three years after treatment , specific exercise group recurrence was 35 % , and control group recurrence was 75 % ( P < 0.01 ) . Conclusion . Long-term results suggest that specific exercise therapy in addition to medical management and resumption of normal activity may be more effective in reducing low back pain recurrences than medical management and normal activity alone Study Design . A prospect i ve study of multifidus images . Objective . To compare the change of the cross-sectional area ( CSA ) of multifidus in subjects with and without chronic low back pain ( LBP ) at different postures . Summary of Background Data . Ultrasound imaging was shown to be useful in assessing acute LBP patients at rest only . Methods and Measures . Thirty-five male adults participated , including 19 normal and 16 chronic LBP patients . The CSAs of multifidus were assessed on ultrasound images acquired on both sides of the L4 and L5 levels with the subjects in prone lying , upright st and ing , and 25 ° and 45 ° forward stooping . Results . In the control group , the CSA of multifidus increased from prone lying to upright st and ing and then gradually decreased from 25 ° to 45 ° forward stooping . However , a reverse pattern of the CSA changes was identified in patients with chronic LBP . Conclusion . Multifidus contracts maximally at upright st and ing in the normal group , while maximum contraction of the muscle occurs at 25 ° forward stooping in the patient group . The role of multifidus may be altered in the stabilization of the lumbar spine of chronic LBP patients . Assessment of the change in muscle size reacting to different postures is found to be helpful OBJECTIVE To compare trunk muscle coordination in people with and without low back pain with varying speeds of limb movement . STUDY DESIGN Abdominal and back extensor muscle activity in association with upper limb movement was compared among three speeds of movement and between people with and without low back pain . PARTICIPANTS Fourteen subjects with a history of recurrent low back pain and a group of age- and sex-matched control subjects . MEASURES The onsets of electromyographic activity of the trunk and limb muscles , frequency of trunk muscle responses , and angular velocity of arm movements . RESULTS Early activation of transversus abdominis ( TrA ) and obliquus internus abdominis ( OI ) occurred in the majority of trials , with movement at both the fast and intermediate speeds for the control group . In contrast , subjects with low back pain failed to recruit TrA or OI in advance of limb movement with fast movement , and no activity of the abdominal muscles was recorded in the majority of intermediate speed trials . There was no difference between groups for slow movement . CONCLUSION The results indicate that the mechanism of preparatory spinal control is altered in people with lower back pain for movement at a variety of speeds Ultrasonography has recently been proposed for assessing changes in thickness and motion of the diaphragm during contraction in humans . Data on ultrasound assessment of abdominal muscles in humans are scarce . We therefore investigated the changes in thickness and the relevant mechanical effects of abdominal muscles using this technique during respiratory manoeuvres in normal subjects . We evaluated the thickness of the abdominal muscle layers in six normal male subjects ( aged 26 - 36 yrs ) using a 7.5 MHz B-mode ultrasound transducer .  Gastric ( Pg ) and mouth pressures , muscle thickness of external oblique ( EO ) , internal oblique ( IO ) , transversus abdominis ( TA ) and rectus abdominis ( RA ) were assessed at functional residual capacity ( FRC ) , residual volume ( RV ) , total lung capacity ( TLC ) , during progressive ( PEEs ) and maximal expiratory efforts ( MEEs ) against a closed airway and during homolateral ( HTR ) and contralateral ( CTR ) trunk rotation . Abdominal muscle thickness was found to be reproducible ( coefficient of variation and two-way analysis of variance ) . Compared to FRC , the thickness of IO , TA and RA significantly increased at RV and during MEEs , whereas EO remained unchanged ; at TLC , the thickness of IO and TA significantly decreased . During PEEs , a significant relationship between increase in Pg and TA thickness was observed in all subjects , the thickness of the other abdominal muscles being inconsistently related to Pg . Finally , a significant increase in the thickness of IO and EO was found during HTR and CTR , respectively . We conclude that during maximal expiratory manoeuvres , transversus abdominis , internal oblique and rectus abdominis thickened similarly . Transversus abdominis seems to be the major contributor in generating abdominal expiratory pressure during progressive expiratory efforts . External oblique seems to be preferentially involved during trunk rotation . These results suggest the possible value of study ing the abdominal muscles by ultrasonography in various respiratory disorders BACKGROUND AND PURPOSE Low abdominal hollowing in four-point kneeling is used clinical ly to test and rehabilitate transversus abdominis ( TrA ) but many people find this exercise difficult to perform . Contracting pelvic floor muscles ( PF ) during low abdominal hollowing may facilitate contraction of TrA. Thickness increase in the abdominal muscles during low abdominal hollowing has been measured with real-time ultrasound scanning and may indicate muscle contraction . The present study investigated the effect of instructing PF contraction on TrA thickness increase during low abdominal hollowing . METHOD Twelve females and eight males with no reported pelvic floor dysfunction or low back pain in the last two years were taught low abdominal hollowing in four-point kneeling . Subjects performed low abdominal hollowing with and without instruction to contract PF in r and om order . Transversus abdominis , obliquus internus ( OI ) and obliquus externus ( OE ) thickness were measured with ultrasound scanning at rest and during both tests . RESULTS Mean increase in TrA thickness during low abdominal hollowing was 49.71 % ( SD 26.76 % ) , during low abdominal hollowing with PF it was 65.81 % ( SD 23.53 % ) . Paired Student 's t-tests indicated a significant difference between tests ( p = 0.015 ) . There were no significant differences between tests for OE or OI thickness increase . CONCLUSIONS Instructing healthy subjects to co-contract PF results in greater increase in TrA thickness during low abdominal hollowing in four-point kneeling . This may indicate greater contraction of TrA and thus be useful for clinicians training TrA. Further research could investigate the validity of change of thickness as a measure of abdominal muscle contraction , investigate the effect of instructing PF co-contraction on TrA in patients with low back pain and measure PF and TrA activity simultaneously This cross-sectional , prospect i ve study aim ed to produce normal reference data for measurements of the lumbar multifidus muscle . A total of 120 subjects , 68 females ( aged 20 - 64 years ) and 52 males ( 20 - 69 years ) were studied . Bilateral transverse ultrasound images were made of multifidus at the fourth and fifth lumbar vertebrae ( L4 & L5 ) . Cross-sectional area ( CSA , cm(2 ) ) and linear dimensions ( AP , anteroposterior ; Lat , lateral ) were measured and the latter expressed as a ratio ( AP/Lat ) to reflect shape . Relationships between CSA and anthropometric measures were examined . Multifidus CSA was larger in males ( P<0.001 ) and age had no effect . The CSA was larger at L5 than L4 ( P<0.001 ) and highly correlated between the two levels ( males r=0.82 , females 0.80 ) . Differences in muscle shape were observed for gender , age and vertebral level . Between-side symmetry was high for size but not shape ( CSA < 10 % difference ) . Linear measurements multiplied ( APxLat ) correlated highly with CSA ( all groups r0.94 , P<0.0001 ) . The AP dimension was also acceptably predictive of CSA at L4 ( r0.79 ) . There were no clinical ly useful correlations between CSA and anthropometric measures . These findings provide normal references ranges for objective assessment of lumbar multifidus . This paper also addresses specific practical issues when scanning multifidus 1 . Human gastrocnemius medialis architecture was analysed in vivo , by ultrasonography , as a function of joint angle at rest and during voluntary isometric contractions up to the maximum force ( MCV ) . maximum force ( MVC ) . 2 . At rest , as ankle joint angle increased from 90 to 150 deg , pennation increased from 15.8 to 27.7 deg , fibre length decreased from 57.0 to 34.0 mm and the physiological cross-sectional area ( PCSA ) increased from 42.1 to 63.5 cm2 . 3 . From rest to MVC , at a fixed ankle joint angle of 110 deg , pennation angle increased from 15.5 to 33.6 deg and fibre length decreased from 50.8 to 32.9 mm , with no significant change in the distance between the aponeuroses . As a result of these changes the PCSA increased by 34.8 % . 4 . Measurements of pennation angle , fibre length and distance between the aponeuroses of the gastrocnemius medialis were also performed by ultrasound on a cadaver leg and found to be in good agreement with direct anatomical measurements . 5 . It is concluded that human gastrocnemius medialis architecture is significantly affected both by changes of joint angle at rest and by isometric contraction intensity . The remarkable shortening observed during isometric contraction suggests that , at rest , the gastrocnemius muscle and tendon are considerably slack . The extrapolation of muscle architectural data obtained from cadavers to in vivo conditions should be made only for matching muscle lengths Study Design . Intrasubject controls with r and omized intervention order . Objective . To quantify the immediate change in posteroanterior ( PA ) spinal stiffness produced by different combinations of trunk muscle contraction . Summary of Background Data . The abdominal hollow and the abdominal brace are 2 different combinations of trunk muscle contractions that are commonly prescribed to increase spinal stability . Unfortunately , the immediate effect of these different contractions on spinal stiffness ( one indicator of spinal stability ) has not yet been quantified directly . Methods . Twenty-eight asymptomatic subjects were taught abdominal hollow and brace contractions then performed them in a r and omized order framed by periods of rest . Surface electromyography and B-mode ultrasound confirmed that all contractions were performed appropriately . During each test condition ( hollow , brace , and rest ) , a noninvasive indentation technique was used to quantify PA spinal stiffness . A repeated measures analysis of variance was used to assess the significance of changes in the PA spinal stiffness between test conditions . Results . Both the abdominal hollow and abdominal brace contractions increased PA spinal stiffness significantly when compared with the rest condition ( P < 0.001 ) . When the abdominal hollow and brace contractions were compared with each other , the abdominal brace contraction produced significantly greater PA spinal stiffness ( P < 0.05 ) . Conclusion . In asymptomatic subjects , the abdominal brace contraction provided an immediate PA stiffening effect that was significantly greater in magnitude when compared with conditions of rest and abdominal hollowing . These findings may allow clinicians to better match commonly prescribed contraction-based interventions with specific patient needs . Future work is required to assess the long-term effect of repeated abdominal brace and hollow contractions on PA spinal stiffness and low back pain Rehabilitative ultrasound imaging ( RUSI ) is considered a valid method to measure muscle activation in key spinal muscles in asymptomatic subjects . Research measuring muscle activation with RUSI in painful subjects is limited . The aim of this study was to determine if changes in muscle activation from experimentally induced pain can be measured by RUSI . Six male subjects performed tasks known to activate the transverse abdominis ( TrA ) and lumbar multifidus ( LM ) while RUSI measurements of muscle thickness were obtained during control and hypertonic saline conditions . The abdominal draw-in maneuver was used to volitionally activate the TrA and a series of upper extremity lifting tasks were used to automatically activate the LM . Pain was induced by injecting 5 % hypertonic saline into the longissimus muscle 
    Output:
    
10 studies investigated criterion-related validity and provided evidence that while ultrasound may be a valid measure of trunk muscle size , the validity of ultrasound to quantify muscle activation is context -dependent , depending on the muscle involved , the contraction strategy utilised , and the intensity of muscle contraction .
It is valid to use rehabilitative ultrasound imaging to measure trunk muscle size and activation during most isometric sub-maximal contractions .
Ultrasound measures appear sensitive to both positive and negative change