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At least 685 records · Page 38Linked to original sources
PubMed2006

Altered patterns of superficial trunk muscle activation during sitting in nonspecific chronic low back pain patients: importance of subclassification.

STUDY DESIGN: A cross-sectional comparative study between healthy controls and two subgroups of nonspecific chronic low back pain (LBP) patients. OBJECTIVES: To determine differences in trunk muscle activation during usual unsupported sitting. SUMMARY OF BACKGROUND DATA: Patients with LBP commonly report exacerbation of pain on sitting. Little evidence exists to confirm that subgroups of patients with nonspecific chronic LBP patients use different motor patterns in sitting than pain-free controls. METHODS: A total of 34 pain-free and 33 nonspecific chronic LBP subjects were recruited. Two blinded clinicians classified nonspecific chronic LBP patients into two subgroups (active extension pattern and flexion pattern). Surface electromyography (sEMG) was recorded from five trunk muscles during subjects' unsupported "usual" and "slumped" sitting. RESULTS: No differences in trunk muscle activity were observed between healthy controls and nonspecific chronic LBP groups for usual sitting. When the classification system was applied, differences were identified. Compared with no-LBP controls, the active extension pattern group presented with higher levels of cocontraction of superficial fibers of lumbar multifidus (12%), iliocostalis lumborum pars thoracis (36%) and transverse fibers of internal oblique (43%). while the flexion pattern group showed a trend toward lower activation patterns (lumbar multifidus, -7%; iliocostalis lumborum pars thoracis, -6%, and transverse fibers of internal oblique, -5%). The flexion relaxation ratio of the back muscles was lower for nonspecific chronic LBP (superficial lumbar multifidus: t = 4.5; P < 0.001 and iliocostalis lumborum pars thoracis:t = 2.7; P < 0.001), suggesting a lack of flexion relaxation for the nonspecific chronic LBP. CONCLUSION: Subclassifying nonspecific chronic LBP patients revealed clear differences in sEMG activity during sitting between pain-free subjects and subgroups of nonspecific chronic LBP patients.

Abdominal Muscles↗
PubMed2003

Vestibular actions on back and lower limb muscles during postural tasks in man.

The vestibular system was activated by galvanic electrical stimulation in 19 normal subjects. With the head turned to one side so that the stimulating anode was on the posterior mastoid process, stimulation caused standing subjects to sway backwards in the sagittal plane. Electromyography showed bilateral activation of erector spinae, gluteus maximus, biceps femoris, soleus and intrinsic foot (toe flexor) muscles. When head direction or electrode polarity was reversed so that the anode was anterior, all those muscles became less active and the subjects swayed forwards. With the head facing forward, stimulation caused sideways sway in the coronal plane, towards the anode, with excitation of the erector spinae on the anode side and reduced activity on the cathode side. The limb muscles were activated on the side opposite the anode and showed complex responses on the anode side. Responses were detectable in the erectores spinae muscles in sitting subjects. No responses in limb muscles were detected in the sitting posture. Subject responses in erector spinae recorded at L3/L4 had latencies from 59 to 110 ms, using a 2 mA stimulus. Latencies in lower limb muscles were longer. The results suggest a role for the vestibular system and descending brain stem motor pathways to the erectores spinae muscles in the control of postural orientation of the back when sitting and standing. The conduction velocity in the motor pathway was estimated to be 13 +/- 10 m s(-1) (mean +/- S.D., n = 12 subjects).

Adult↗
PubMed2003

Lumbar muscle fatigue and recovery in patients with long-term low-back trouble--electromyography and health-related factors.

OBJECTIVE: The aim was to explore the validity and reliability of EMG for assessing lumbar muscle fatigue. DESIGN: Patients with long-term low-back trouble (n=57) were compared to a healthy reference group (n=55). Back muscle fatigue and recovery were studied in relation to health-related factors. BACKGROUND: EMG spectral variables are important tools in the assessment of patients with low-back trouble. The influence of disability on these variables needs further investigation. METHODS: EMG from the lower back muscles was recorded during a 45 s trunk extension at 80% of maximal voluntary contraction torque and during recovery. Disability was studied using questionnaires. RESULTS: The reliability was high for maximal voluntary contraction torque and EMG initial median frequency, lower for the median frequency slope, and insufficient for median frequency recovery half-time. The patients had lower maximal voluntary contraction torque, higher initial median frequency at L5 level, flatter slope, and longer recovery half-time than the healthy subjects did. However, for subjects with significantly negative slope, indicating fatigue, there was no significant difference in slope between patients and healthy subjects, while, for subjects without such fatigue, patients showed significantly flatter slopes at L5. The sensitivity/specificity of the test was 86%/78%. The most significant variables selected with logistic regression were maximal voluntary contraction torque and initial median frequency at L5. Patients without significantly negative slopes during contraction and/or not exponential-like EMG recovery scored worse on several items concerning disability and self-efficacy. CONCLUSIONS: EMG spectral variables in combination with torque might be used for classification. For patients with long-term low-back trouble, the ability to fatigue the lumbar muscles sufficiently to obtain a significantly negative slope during an 80% maximal voluntary contraction may be a sign of better functioning. RELEVANCE: The ability to fatigue the back muscles during a test requiring a high force output might be achieved with back muscle training focused on increasing strength and self-efficacy.

Adaptation, Physiological↗
PubMed2005

Trunk muscle co-ordination during gait: relationship between muscle function and acute low back pain.

Low back pain costs billions of Euros annually in all industrialized countries. Often radiological diagnosis fails to give evidence of the pathogenesis of low back pain. Although psychophysiological characteristics have an influence, it seems that insufficient muscular spinal stabilization may play the major role in the development of low back pain. Assessment of trunk muscle stabilization activity during everyday activities is rare. Therefore, in this study healthy persons were investigated during walking on a treadmill at a speed of 4 km/h. Women (n = 16) with no history of back pain were investigated before and after a static loading situation of the spine, i.e. while wearing a waistcoat. After this loading situation four women developed pain (pain subjects). Surface EMG (SEMG) was taken from five trunk muscles of both sides. Grand averaged amplitude curves over stride, amplitude normalized curves and variation between all included strides were calculated for all muscles and subjects, respectively. The normal range of all calculated parameters was defined within the span between the 5th and the 95th percentiles of all pain free subjects. Data were evaluated according to deviations from the normal range. Already before the load situation, pain subjects showed considerable deviations from the normal range, mainly of their abdominal muscles. There was no relationship between magnitude of deviation and pain intensity, but perceived exertion was highest in those subjects who showed the most symptoms in terms of number of muscles being identified as considerably deviating from the normal range. No specific "dysfunction pattern" could be identified, which argues for highly individual mechanisms instead of a single target muscle. The results suggest cumulative effects of different disturbance levels resulting in acute back pain. Since deviations could be identified already before the pain occurred, disturbed muscle function seems to be a risk factor for developing back pain. Further investigations aimed at clear identification of and, as a second step, correction of muscle function are necessary.

Journal Article↗
PubMed1995

Muscle activity and low back loads under external shear and compressive loading.

STUDY DESIGN: This study analyzed anatomic and neural control characteristics of the trunk musculature. Subjects were exposed to external shear and compressive loads with equivalent moments to evaluate activation patterns and loading on the low back. OBJECTIVES: The migration of activity between the thoracic and lumbar erector spinae muscle groups was examined to determine whether the motor control system chooses to minimize joint loading by recognizing differences in moment, compression, and shear support requirements and assigning muscle activation in the most appropriate way. SUMMARY OF BACKGROUND DATA: Loads were applied either parallel or perpendicular to the low back to create compressive or shear forces. No previous study has attempted to isolate the response of the trunk musculature with the type of external load. METHODS: Eleven male subjects isometrically held an external load that was altered to create either a compressive or an anterior shear load on the low back but with equal extensor (reaction) moments (experiment 1). In a second experiment four men repeated the task with an increased range of applied loads (5-25 kg) together with measurements of intra-abdominal pressure. RESULTS: The tasks with a compressive external load resulted in significantly higher levels of activation for all seven electromyographic channels recorded. Intraabdominal pressure, compressive and shear joint forces were all higher in the compression loading method when equal loads and low back moments were compared. CONCLUSIONS: It was concluded that the motor control system does not arrange muscle activation levels in a way to minimize lumbar spinal loading at least for the relatively low levels of this study. Biomechanical models that use the objective criterion of minimum joint load may not be representative of the motor control system, at least in the low back.

Abdominal Muscles↗
PubMed1988

The effect of voluntary diaphragmatic activation on back lifting.

The effect of increased intraabdominal pressure upon the activation of the erector spinae muscles during back lifting was studied in 10 healthy volunteers. The intraabdominal pressure was increased by voluntary prelifting coactivation of the diaphragm and the abdominal muscles. EMG was recorded with surface electrodes over the diaphragm and the erector spinae, abdominal and intercostal muscles. The EMG signals were rectified and averaged from 20 lifts of 10 kg with and without pressurization to give mean level of activity during 2 s before lifting and during successive angular positions of the trunk during lifting. In 7 of the 10 subjects the pre-lifting coactivation of diaphragm and abdominal muscles reduced erector spinae activity at lift-off and/or during the trunc erecting movement. An increased intraabdominal pressure thus often has an unloading effect on the erector spinae muscle during back lifting.

Abdomen↗
PubMed1999

Back and hip extensor muscle function during therapeutic exercises.

BACKGROUND: Therapeutic exercises are widely used in the treatment of low back problems. Clinical knowledge about targeting the load in these exercises, however, is insufficient. This study assessed the L2 and L5 level paraspinal and gluteus maximus muscle activities in different therapeutic exercises. Intramuscular and surface electromyography (EMG) measurements were obtained to study whether surface EMG measurements can be used in the assessment of multifidus muscle function. METHODS: Eleven healthy subjects (5 men, 6 women) 21 to 38 years of age volunteered for the study. The subjects performed 18 different therapeutic exercises. During the exercises paraspinal EMG was recorded using fine wire and surface electrodes. The normalized peak and average muscle EMG activities (percentage of amplitude in maximal voluntary contraction [MVC]) during each task were determined. RESULTS: The correlations between the average intramuscular and surface activities of the normalized EMG (% of MVC) at the L2 and L5 levels were .928 and .950, respectively. The peak and average EMG amplitudes of the exercises were below 50% and 25% of MVC, respectively. At the L5 level, the multifidus peak and average EMG amplitudes (% MVC) were higher in women than in men, whereas no significant difference was found at the L2 level. In women, the normalized multifidus EMG amplitude was higher at the L5 level than at the L2 level, whereas no significant difference was found in men. In both sexes, the normalized EMG amplitude was higher in the multifidus than in the longissimus muscle. CONCLUSION: Surface EMG measurements may be used in the assessment of multifidus muscle function. Simple therapeutic exercises are effective in activating the lumbar paraspinal muscles.

Adult↗
PubMed1987

A technique for measuring the mechanical actions of heterogenic (intermuscular) reflexes in the decerebrate cat.

Two muscle pullers were used to study the natural mechanical actions of autogenic reflexes, which arise from muscle receptors and feed back to the muscle of origin, and heterogenic reflexes, which feed back to muscles other than the muscle of origin. In the study reported here, the reflexes associated with muscles which act about the ankle joint of the decerebrate cat were investigated. Actions of autogenic pathways were measured by imposing length changes on the muscle and recording the resulting changes in force and EMG (electromyogram). Actions of heterogenic reflexes for pairs of muscles were measured by imposing appropriate combinations of length changes on the muscle of origin and on the muscle receiving the heterogenic reflex. In some cases, length changes were applied in such a way as to mimic normal mechanical coupling to evaluate the physiological importance of the reflexes, while in other cases the tests departed from normal coupling to address questions about mechanisms of reflex action. It was found that several pairs of muscles could be studied in a single experiment so that supraspinal influences on the pattern of spinal reflex connectivity can be conveniently evaluated.

Animals↗
PubMed2000

The relationship between lower extremity injury, low back pain, and hip muscle strength in male and female collegiate athletes.

OBJECTIVE: To determine the relationship of previous lower extremity (LE) injury and/or low back pain (LBP) on hip abduction and extension strength. DESIGN: Cohort study of college athletes at time of preparticipation screening physical. SETTING: An NCAA Division I college. PARTICIPANTS: Two hundred ten college athletes (140 males and 70 females) from an NCAA Division I school. MAIN OUTCOME MEASURES: Mean and maximal hip abduction and extension strengths were recorded using a specially designed dynamometer anchoring station. Previous injury to the LE or LBP in the past year was recorded via personal interview at the time of screening and verified by review of previous injury records. RESULTS: A significant difference in side-to-side symmetry of maximum hip extension strength was observed in female subjects who reported LE injury or LBP as compared to those who did not. Side-to-side difference in hip strength, however, did not differ between male athletes, regardless of reported LE injury or LBP status. CONCLUSION: Female athletes appear to have a differing response of the proximal hip musculature to LE injury or LBP, as compared with their male counterparts. Research is under way to further validate these findings. CLINICAL RELEVANCE: This study provides some reasoning to support the screening of hip strength during the preparticipation physical, as it may be important in the prevention of LE injury and LBP in collegiate athletes.

Adult↗