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PURPOSE: Roman chair exercises are popular for improving back muscle endurance but do not specifically target back muscles. This study aimed to determine whether an adaptation of the Roman chair exercise would induce more fatigue in back muscles than in hip extensors. METHODS: For this study, 16 healthy subjects and 18 patients with nonspecific chronic low back pain performed trunk flexion-extension cycles until exhaustion in a Roman chair with hips flexed at 40°. Surface EMG signals were recorded bilaterally on four back muscles and two hip extensors (gluteus maximus and biceps femoris). Motion analysis of the trunk segments (pelvis, lumbar, and thoracic spines) was also carried out. RESULTS: In both groups, EMG revealed clear evidence of muscle fatigue for the gluteus maximus, less clear evidence of fatigue for the lower back muscles, and motor unit recruitment (without fatigue) for the upper back muscles and biceps femoris. A change of muscle activation pattern was emphasized throughout the exercise bout, with some lower back muscles showing an increase followed by a decrease or leveling off of activation and with upper back muscles showing an increased activation at the end. Kinematic analyses revealed a progressive decrease (11°) in the lumbar range of motion (ROM) and a progressive increase in hip (2°) and thoracic (7°) ROM during the exercise bout. CONCLUSIONS: Roman chairs allow more freedom to change the kinematics of the spine during the exercise (less lumbar and more thoracic motion) to delay lower back muscle fatigue by sharing the load between the lower and upper back muscles. Even with adaptations to reduce hip extensors fatigue, this may make this exercise not as specific as wanted for fatiguing lower back muscles.

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PURPOSE: To determine whether dynamic back muscle endurance exercises in a semisitting position induce more fatigue in back muscles than that in hip extensors in healthy controls as well as in patients with nonspecific chronic low back pain. METHODS: Sixteen healthy volunteers and 18 volunteers with nonspecific chronic low back pain performed trunk flexion-extension cycles until exhaustion at 60% of their strength in a machine designed for back exercise in a semisitting position with knees' angle at 135 degrees . The number of cycles and perceived muscle fatigue (Borg CR-10 scale) at five areas (upper and lower back, gluteus, hamstrings, and quadriceps) were used as fatigue criteria. EMG signals were recorded bilaterally on four back muscles, two hip extensors (gluteus maximus and biceps femoris), and the vastus medialis. The slope values of the instantaneous median frequency values computed over time were retained as EMG indices of fatigue. RESULTS: The number of cycles was equivalent in healthy controls (n = 23 +/- 13) and patients with back pain (n = 27 +/- 16). EMG indices of fatigue disclosed evidence of muscle fatigue in all the back muscles and the vastus medialis, contrary to hip extensors. EMG revealed significantly more muscle fatigue of lower back muscles, which was further corroborated by the Borg scale assessment. No between-group difference was obtained in any EMG comparison. CONCLUSION: These results showed that this type of exercise machine can specifically train the back muscles, and this as much in subjects with nonspecific chronic low back pain as in healthy controls. This has implications for the training of back muscle endurance, especially in patients with back pain for whom poor back muscle endurance is sometimes of concern.

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OBJECTIVE: To assess the effect of pelvic stabilization and hip position on the electromyographic activity of trunk extensors during Roman chair exercise. A secondary objective was to compare genders. DESIGN: Repeated measures. SUBJECTS: Eleven men and 11 women volunteers. METHODS: Five trunk flexion-extension cycles for 3 Roman chair conditions: (i) pelvis unrestrained; (ii) pelvis restrained; and (iii) hip at 40 degrees flexion. Electromyographic signals were recorded on the back muscles, as well as on the gluteus maximus and biceps femoris. The percentage of electromyographic amplitude relative to the maximal activity was used to assess the level of muscular activation of each muscle group across the exercises. RESULTS: For both genders, the Roman chair conditions did not influence the activity of the back and gluteus muscles. The hip-at-40 degrees-flexion condition significantly reduced the activity of the biceps femoris (average of 4-18%) relative to the other 2 conditions. Gender differences were observed on the activity of the biceps femoris in all Roman chair conditions. CONCLUSION: The hip-at-40 degrees-flexion condition would allow the Roman chair exercise to train the targeted back muscles more specifically by overloading them over a longer duration in order to induce physiological changes.

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PURPOSE: To examine the effect of pelvic stabilization and two lower-limb configurations on the EMG activity of back and hip extensor muscles during a dynamic back extension exercise on a machine and to compare them between sexes. METHODS: Twenty-two healthy volunteers (11 men and 11 women) performed five trunk flexion-extension cycles at 40% of their maximal voluntary contraction (MVC) in a machine designed for back exercise. Two different positions were used: 1) seated position (seat horizontal, knees at 90 degrees ) and 2) semisitting position (seat slightly tilted forward at 15 degrees , knees at 45 degrees of flexion). In each position, three pelvic stabilization conditions were tested: 1) unrestrained (control condition), 2) partially restrained (posteriorly), and 3) totally restrained (posteriorly and anteriorly). EMG signals were recorded bilaterally with 12 pairs of electrodes placed on back muscles as well as on the gluteus maximus and biceps femoris. The muscular activation level, that is, the percentage of EMG amplitude relative to the maximal EMG obtained from MVC, was used to asses the relative contribution of each muscle group across exercises. RESULTS: In both sexes, two main results were found: 1) pelvic stabilization (partially and totally restrained) significantly (P < 0.05) increased the activity of all back muscles (average of 12%) and 2) semisitting position significantly decreased (range = 8-27%) the activity of two hip extensors compared with the seated position. Sex differences were also observed relative to the activity of some back muscles as well as the biceps femoris. CONCLUSIONS: Combining pelvic stabilization and semisitting position in back exercise machines might be a useful way to localize the effects of endurance training at the back muscles and this in both the sexes.

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BACKGROUND CONTEXT: Back muscles capacity is impaired in chronic low back pain patients but no motivation-free test exists to measure it. A functional endurance test (FET) was used to assess capacity of back muscles using surface electromyographic (EMG) indices as outcome measures. PURPOSE: The main objective of the present study was to explore the possibility of combining different types of EMG indices to predict absolute endurance and strength. STUDY DESIGN/SETTING: A cross-sectional study using a repeated measures design in laboratory setting. METHODS: Healthy subjects (44 men and 29 women) performed maximal voluntary contractions (Strength criterion: extension moment at L5/S1) and a fatigue test involving intermittent static extension contractions to exhaustion (Tend endurance criterion: time to reach exhaustion). Surface EMG signals were collected from four pairs of back muscles. From the first 5 minutes (women) or 10 minutes (men) of EMG data, frequency- and temporal-domain analyses were applied to compute various EMG indices. RESULTS: Strength values ranged from 153 to 508Nm, whereas Tend values ranged from 3 to 57 minutes across the subjects. Gender-specific multiple regression equations were developed, using the retained EMG indices from the four electrode sites, to predict Tend (men: R(2)=0.76, error=9%; women: R(2)=0.70, error=17%) and Strength (men: R(2)=0.72, error=9%; women: R(2)=0.25, error=13%). CONCLUSIONS: It appears to be possible to predict the capacity of back muscles using an intermittent and time-limited (submaximal) fatigue task. Frequency- and temporal-domain EMG indices were shown to provide complementary information in this respect. This FET has potential to better infer back muscle capacity for realistic occupational tasks because more specific muscle fatigue mechanisms are involved.

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BACKGROUND: Electromyographic (EMG) amplitude ratios (EMG-ratios) have been proposed to assess back muscle coordination in chronic low back pain patients to avoid the normalization of EMG using maximal contractions. The aim of this study was to test the relevance of this type of EMG analysis. METHODS: Healthy subjects (44 men and 13 women) and patients with chronic low back pain (57 men) performed three 7s static ramp extension contractions ranging from 0% to 100% of the maximal voluntary contraction while standing in a static dynamometer. A subgroup of 20 healthy men also performed 5s step contractions at 10%, 20%, 40%, 60% and 80% of the maximal voluntary contraction. Finally, to assess reliability, another subgroup (n=20 healthy and 20 men with chronic low back pain) performed the protocol three times, on different days. Surface EMG signals were collected from four pairs of back muscles and subcutaneous tissue thickness was measured at the corresponding electrode sites. EMG amplitude values were computed at each 5% force level from 10% to 80% of the maximal voluntary contraction. Then, EMG-ratios were computed between different electrode sites and averaged bilaterally. FINDINGS: All EMG-ratios were affected by the force level and the contraction type (ramp vs step contractions). Statistically significant Pearson's correlations (r=-0.38 to -0.57) were obtained between some EMG-ratios and their corresponding subcutaneous tissue thickness ratios. The reliability of the EMG-ratio variables ranged from moderate to excellent (intra-class correlation coefficients between 0.50 and 0.91). Comparisons between 12 men and 13 women and between 24 healthy men and 57 men with chronic low back pain showed that EMG-ratios were sensitive to sex but not to pain status. Multivariate analyses applied on the EMG-ratios identified clusters of subjects but none of the main clinical variables were able to clearly characterize these clusters. INTERPRETATION: Overall, even though additional research is warranted to further substantiate some important psychometric characteristics of the EMG-ratios as well as their biomechanical and clinical significance, these results support their use for assessing the coordination patterns of back muscles, provided that confounding variables such as the force level, the contraction type, and subcutaneous tissue thickness are accounted for.

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INTRODUCTION: In a previous paper, standard surface electromyographic (EMG) indices of muscle fatigue, which are based on the lowering of the median or mean frequencies of the EMG power spectrum in time, were applied during an intermittent absolute endurance test and were evaluated relative to criterion validity and test-retest reliability. The aims of this study were to assess mechanical and alternative EMG correlates of muscle fatigue. METHODS: Healthy subjects (44 males and 29 females; age: 20-55 yrs) performed three maximal voluntary contractions (MVC) and an endurance test while standing in a static dynamometer. Surface EMG signals were collected from four pairs of back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). The test, assessing absolute endurance (90 Nm torque), consisted of performing an intermittent extension task to exhaustion. Strength was defined as the peak MVC whereas our endurance criterion was defined as the time to reach exhaustion (Tend) during the endurance test. Mechanical indices quantifying physiological tremor and steadiness were computed from the dynamometer signals (L5/S1 extension moments) along with EMG indices presumably sensitive to variable load sharing between back muscle synergists during the endurance test. RESULTS: Mechanical indices were significantly correlated to Tend (r range: -0.47 to -0.53) but showed deceiving reliability results. Conversely, the EMG indices were correlated to Tend (r range: -0.43 to -0.63) with some of them particularly correlated to Strength (r=-0.72 to -0.81). In addition, their reliability results were acceptable (intra-class correlation coefficient >0.75; standard error of measurement <10% of the mean) in many cases. Finally, several analyses substantiated their physiological relevance. These findings imply that these new EMG indices could be used to predict absolute endurance as well as strength with the use of a single intermittent and time-limited (5-10min) absolute endurance test, a practical way to assess the back capacity of chronic low back pain subjects.

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Electromyographic (EMG) contralateral imbalances of back muscles are often interpreted as an aberrant back muscle pattern related to back pain. This study assessed different measurement properties (influence of the control of asymmetric efforts and of the force level, reliability, and sensitivity to low back status) of EMG imbalance parameters. Healthy controls (n = 34) and chronic low back pain subjects (n = 55) stood in a dynamometer measuring the principal (extension) and coupled (lateral bending, axial rotation) L5/S1 moments during isometric trunk extension efforts. The results showed that back pain subjects did not produce higher coupled moments than controls. Providing feedback of the axial rotation moment to correct asymmetric efforts during the task did not reduce EMG contralateral imbalances, except for some extreme cases. Normalized EMG imbalance parameters remain relatively constant between 40% and 80% of the maximal voluntary contraction. The reliability of EMG imbalance parameters was moderate, at best. Finally, neither low back status nor pain location had an effect on EMG contralateral imbalances. We conclude that the clinical relevance of EMG contralateral imbalances of back muscles remains to be established.

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OBJECTIVE: To compare the sensitivity of 3 different back test protocols in measuring differences in strength and fatigue between subjects with and without chronic low back pain (CLBP). DESIGN: Descriptive study using a repeated-measures design. SETTING: A research laboratory within a rehabilitation center. PARTICIPANTS: Eighteen healthy subjects and 13 subjects with CLBP were assessed in a single session to compare the 3 protocols. The protocols were an upright position test (UPP), a semicrouched lifting test (LIF), and the Sorensen fatigue test. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Moments of force and surface electromyography were recorded bilaterally from 4 homologous back muscles while the subjects performed static trunk extension efforts for each protocol. Fatigue was quantified by the slopes of the linear regression of electromyography time-series. RESULTS: The back muscle fatigue and strength scores did not differ significantly for the 2 subject groups for any of the 3 protocols. The electromyography fatigue indices revealed that the Sorensen fatigue test and UPP produced more fatigue in the back muscles than the LIF. CONCLUSIONS: It was impossible to specify which protocol is more sensitive to low back status because no between-group difference was observed for any of the 3 tests.

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BACKGROUND: It is known that the back muscles of scoliotic subjects present abnormalities in their fiber type composition. Some researchers have hypothesized that abnormal fiber composition can lead to paraspinal muscle dysfunction such as poor neuromuscular efficiency and muscle fatigue. EMG parameters were used to evaluate these impairments. The purpose of the present study was to examine the clinical potential of different EMG parameters such as amplitude (RMS) and median frequency (MF) of the power spectrum in order to assess the back muscles of patients presenting idiopathic scoliosis in terms of their neuromuscular efficiency and their muscular fatigue. METHODS: L5/S1 moments during isometric efforts in extension were measured in six subjects with idiopathic scoliosis and ten healthy controls. The subjects performed three 7 s ramp contractions ranging from 0 to 100% maximum voluntary contraction (MVC) and one 30 s sustained contraction at 75% MVC. Surface EMG activity was recorded bilaterally from the paraspinal muscles at L5, L3, L1 and T10. The slope of the EMG RMS/force (neuromuscular efficiency) and MF/force (muscle composition) relationships were computed during the ramp contractions while the slope of the EMG RMS/time and MF/time relationships (muscle fatigue) were computed during the sustained contraction. Comparisons were performed between the two groups and between the left and right sides for the EMG parameters. RESULTS: No significant group or side differences between the slopes of the different measures used were found at the level of the apex (around T10) of the major curve of the spine. However, a significant side difference was seen at a lower level (L3, p = 0.01) for the MF/time parameter. CONCLUSION: The EMG parameters used in this study could not discriminate between the back muscles of scoliotic subjects and those of control subject regarding fiber type composition, neuromuscular efficiency and muscle fatigue at the level of the apex. The results of this pilot study indicate that compensatory strategies are potentially seen at lower level of the spine with these EMG parameters.

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The purpose of this study was to assess (1) the reliability and (2) the sensitivity to low back pain status and gender of different EMG indices developed for the assessment of back muscle weakness, muscle fiber composition and fatigability. Healthy subjects (men and women) and chronic low back pain patients (men only) performed, in a static dynamometer, maximal and submaximal static trunk extension tasks (short and long duration) to assess weakness, fiber composition and fatigue. Surface EMG signals were recorded from four (bilateral) pairs of back muscles and three pairs of abdominal muscles. To assess reliability of the different EMG parameters, 40 male volunteers (20 controls and 20 chronic low back pain patients) were assessed on three occasions. Reliable EMG indices were achieved for both healthy and chronic low back pain subjects when specific measurement strategies were applied. The EMG parameters used to quantify weakness and fiber composition were insensitive to low back status and gender. The EMG fatigue parameters did not detect differences between genders but unexpectedly, healthy men showed higher fatigability than back pain patients. This result was attributed to the smaller absolute load that was attributed to the patients, a load that was defined relative to their maximal strength, a problematic measure with this population. An attempt was made to predict maximal back strength from anthropometric measurements but this prediction was prone to errors. The main difficulties and some potential solutions related to the assessment of back muscle intrinsic properties were discussed.

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OBJECTIVES: (1) To develop a multiple regression equation using anthropometric measurements to predict back strength and (2) to estimate the effect of practice on the back strength results and back strength predictions. DESIGN: Comparative study with repeated measures performed on three days. BACKGROUND: The assessment of back muscle relative endurance (% maximal strength) requires the measurement of maximal back strength which is problematic with low back pain patients. METHODS: The back strength (L5/S1 static extension moment), age and 26 anthropometric parameters were obtained from 83 male volunteers [42 healthy subjects and 41 chronic low back pain patients] aged between 20 and 60 years. A subsample of 20 healthy subjects and 20 patients were assessed through three days of testing to evaluate the variations of back strength with practice. RESULTS: The final regression model (n=42 healthy subjects) explained 39% of the variance in back strength. Back strength increased with practice (Day1

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The purpose of the present study was to evaluate if rest intervals of 10 or 15 min allow the back muscles to recover completely, from an electromyographic (EMG) point of view, after performing a fatiguing contraction. Twelve healthy males stood in a dynamometer with the trunk in a vertical position and performed three trunk extension fatiguing trials (30 s contractions sustained at 75% of the maximal voluntary contraction) separated successively by a 15 min (between trial 1 and 2) and a 10 min (between trial 2 and 3) rest period. The EMG signals from four pairs of back muscles were collected at 2,048 Hz with active surface electrodes. Different EMG indices computed from the temporal and frequency domains of the EMG signal were considered to evaluate muscular fatigue and recovery from trial 1 to trial 2 and from trial 2 to trial 3. No significant differences (one-way ANOVAs between the three trials, alpha=0.05) were obtained for the different EMG indices computed. The percentage of variance explained by the inter-trial effect was none in most cases, corroborating that no systematic error was present between the trials and suggesting that complete muscle recovery was allowed with 10 or 15 min rest periods. These results support the use of rest periods of 10 to 15 min between multiple fatigue tests, at least for back muscles and for high intensity short duration fatigue tasks as the one used in the present study.

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OBJECTIVE: To assess the reliability and construct validity of various electromyographic indices developed to assess back muscle weakness and muscle fiber composition. DESIGN: A prospective study with repeated measures performed on 3 days along with comparisons of groups presenting different back strength and/or back muscle fiber composition. SETTING: A biomechanics laboratory within a rehabilitation center. PARTICIPANTS: Forty male volunteers (20 healthy, 20 with chronic low back pain) were assessed on 3 different days to assess reliability and to make group comparisons. Thirteen healthy women were also assessed once to obtain a third group with known lower strength and different back muscle fiber composition. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Surface electromyography was recorded for 4 pairs of homologous back muscles while the subjects performed, on a dynamometer, static trunk extension efforts. Electromyographic parameters were computed to assess muscle weakness and muscle fiber composition. The reliability of the data collected across the 3 sessions and comparisons between groups were determined. RESULTS: Electromyographic parameters generally showed good to excellent reliability, but were insensitive to differences in back muscle strength and did not appear to be related to muscle composition. Some trends were observed in the electromyographic parameters across the force levels, but the large interindividual variability impeded statistical comparisons. CONCLUSIONS: The assessment of muscle weakness and muscle fiber composition through electromyographic analysis does not appear feasible, at least on an individual basis, for the muscles of the back.

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