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At least 181 records · Page 10Linked to original sources
PubMed2000

Wavelet and short-time Fourier transform analysis of electromyography for detection of back muscle fatigue.

Measurement of the time-varying characteristics of the frequency content of trunk muscle electromyography is a method to quantify the amount of fatigue endured by workers during industrial tasks, as well as a tool that may guide the training and rehabilitation of healthy and injured workers. Quantification of the change of signal power within specific frequency ranges may shed greater insight into the fatigue process. Sixteen healthy male subjects performed isometric trunk extension at 70% of their maximum voluntary contraction. Surface electromyography from medial and lateral erector spinae, and latissimus dorsi locations were processed using the short-time Fourier transform (STFT) and wavelet transform. Linear regression quantified the time rate of change of median frequency as well as frequency specific STFT filter and wavelet scale measures. The median frequency from the short-time Fourier transform declined by 22 Hz/min from an initial value of 77 Hz on average. The wavelet and STFT filter measures demonstrated this decline to be caused by a reduction in 209-349 Hz signal power in addition to an increase in 7-88 Hz signal power. A significant reduction in median frequency and significant elevation in 13-22 Hz wavelet signal component was detected in about 90% of the cases, indicating their use for detecting and quantifying fatigue.

Adult↗
PubMed1998

EMG recordings of abdominal and back muscles in various standing postures: validation of a biomechanical model on sacroiliac joint stability.

In a biomechanical model we described that for stability of the flat sacroiliac joints (SIJ) muscle forces are required which press the sacrum between the two hip bones (self-bracing). Shear loading of these joints is caused by gravity and longitudinally oriented muscles. Protection against shearing can come from transversely oriented muscles like the internal oblique (OI) abdominal muscles. For validation we used standing postures with significantly more or less OI activity compared to activity in a standardized erect standing reference posture. OI activity decreased significantly when (a) resting on one leg (the contralateral), as can be observed at bus stops, (b) tilting the pelvic backward and (c) applying a pelvic belt. We explain this decrease of OI activity by, respectively, decrease of gravity load, decrease of load from the psoas major muscles, and a substitute of self-bracing. The outcome of this study is in line with the biomechanical model on SIJ stability. Clinical relevance of this study regards aspecific low back pain and is found in the effect of the use of a pelvic belt, of a trunk position as adopted when wearing a small rucksack and of the benefit of exercising trunk muscles in extension and torsion.

Abdominal Muscles↗
PubMed1998

EMG assessment of back muscle function during cyclical lifting.

A new approach to estimating the frequency compression of the surface EMG signal during cyclical dynamic exercise is described. The basic properties of the method are first developed using simulated EMG signals. Spectral compression is measured by defining the instantaneous median frequency from time-frequency representations of the signal derived from a transformation of the Cohen class. The technique is then used to process real EMG signals from paraspinal muscles during repetitive lifting. Our purpose was to use this new procedure to identify (a) whether changes in the instantaneous median frequency among concurrently active paraspinal muscles during repetitive trunk extension produces a 'fatigue pattern' that is indicative of normal functioning, and (b) whether this pattern is different when the subject produces a sustained isometric trunk extension. Four healthy subjects (26 +/- 4 years; 3 males, 1 female) were tested in both a Back Analysis System, for the production of a sustained static isometric contraction, and a LIDO-Lift Controller (Loredan), for repetitive lifting and lowering of a weighted box. EMG signals were recorded concurrently from six bilateral lumbar paraspinal regions during these tasks. The results demonstrate that static and dynamic tasks result in very different patterns of EMG spectral changes, suggestive of differences in load-sharing and underlying metabolic fatigue processes. Unlike the linear decrease in median frequency observed for static contractions, during dynamic contractions instantaneous median frequency behavior is non-linear and more complex. Examples are provided in which distinct periods of instantaneous median frequency decay are followed by periods of recovery during a single trial of repetitive lifting. It is hypothesized that this difference reflects a complex strategy of utilizing muscle load-sharing during strenuous dynamic exercise to provide periods of metabolic recovery that limit localized fatigue. New analysis procedures to characterize this complex behavior are needed to enhance the technique for assessment of impairment in patients with lower back pain.

Adult↗
PubMed2004

The role of back muscle endurance, maximum force, balance and trunk rotation control regarding lifting capacity.

Evaluation of lifting capacity is widely used as a reliable instrument in order to evaluate maximal and safe lifting capacity. This is of importance in regard to planning rehabilitation programs and determining working ability. The aim of this study was to investigate the influence of basic functions on the lifting capacity measured by the progressive isoinertial lifting evaluation (PILE) and the functional capacity evaluation (FCE) tests in a lower (floor to waist) and an upper (waist to shoulder) setting and compare the two test constructs. Seventy-four female subjects without acute low back pain underwent an examination of their lifting capacities and the following basic functions: (1) strength and endurance of trunk muscles, (2) cardiovascular endurance, (3) trunk mobility and (4) coordination ability. A linear regression model was used to predict lifting capacity by means of the above-mentioned basic functions, where the F statistics of the variables had to be significant at the 0.05 level to remain in the model. Maximal force in flexion showed significant influence on the lifting capacity in both the PILE and the FCE in the lower, as well as in the upper, lifting task. Furthermore, there was a significant influence of cardiovascular endurance on the lower PILE and also of endurance in trunk flexion on the lower FCE. Additional inclusion of individual factors (age, height, weight, body mass index) into the regression model showed a highly significant association between body height and all lifting tasks. The r (2) of the original model used was 0.19/0.18 in the lower/upper FCE and 0.35/0.26 in the lower/upper PILE. The model r (2) increased after inclusion of these individual factors to between 0.3 and 0.4. The fact that only a limited part of the variance in the lifting capacities can be explained by the basic functions analyzed in this study confirms the assumption that factors not related to the basic functions studied, such as lifting technique and motor control, may have a strong influence on lifting capacity. These results give evidence to suggest the inclusion of an evaluation of lifting capacity in clinical practice. Furthermore, they raise questions about the predictive value of strength and endurance tests in regard to lifting capacity and work ability.

Back↗
PubMed1986

Investigations of the time series structure of the EMG during sustained isometric contractions of back muscles.

The experiment aimed at elucidating electromyographic signs of fatigue of lumbar muscles. On two days, 4 subjects had to hold 4 different target forces to fatigue. Bipolar surface EMG's were derived at the L3 level. The time series structure of the EMG's was characterized by means of autoregressive models. The r.m.s.- value did not reveal uniform time-dependent changes, except for an increase during the highest force level. The variance explained by a linear stochastic process systematically increased during the sustained contractions. The mean power frequencies exhibited similar changes.

Adult↗
PubMed1987

Brainstem reticular stimulation facilitates back muscle motoneuronal responses to pudendal nerve input.

In urethane or pentobarbital anesthetized female rats, stimulation with bipolar electrodes in the medullary reticular formation evoked activity in lateral longissimus muscle nerves, when trains of pulses were applied. Combined stimulation of the medullary reticular formation and the pudendal nerve revealed a marked mutual facilitation of their two separate effects on the excitability of the lateral longissimus muscle nerves. These results match previous conclusions based on the effects of spinal column transection on the pudendal nerve-evoked response, and are consistent with a role for this mutual facilitation in the control of lordosis behavior.

Animals↗
PubMed1978

Observations on stretch reflexes in lumbar back muscles of the cat.

Reflex responses to brief muscle stretch and to electrical stimulation of dorsal roots were studied in cat longissimus and iliocostalis muscles by myographic and electromyographic recordings in spinal and anesthetized preparations. Brief stretch applied simultaneously to both muscles, by pulling at an isolated segment of the iliac bone, elicited contractions only in the central region of longissimus, composed of slowly contracting fibers, the time to peak tension varying between 70 and 100 ms. No reflex responses were observed in the faster contracting parts of this muscle or in the iliocostalis under the stimulation conditions used. The total reflex time usually varied from 4.5 to 7 ms which is shown to correspond to intra-spinal conduction times, approximately between 2 and 5 ms. Only exceptionally was a central reflex delay corresponding to a monosynaptic transmission observed. Reflexes evoked by dorsal root simulation (L4, L5) have a central conduction time similar to those elicited by adequate stimulation. The possibility that the central pathway for stretch reflexes in longissimus may involve more than two neurons is considered. In decerebrate preparations the central region of longissimus displays a prominent tonic stretch reflex. With the longissimus in situ the magnitude of the reflex is highly dependent on the position of the lumbar spine relative to the pelvic girdle.

Anesthesia↗
PubMed2002

Fatigue-induced change in corticospinal drive to back muscles in elite rowers.

This study examined post-exercise changes in corticospinal excitability in five 'elite' rowers and six nonrowers. Transcranial magnetic stimulation (TMS) was delivered to the motor cortex and bilateral electromyographic (EMG) recordings were made from erector spinae (ES) muscles at L3/L4 spinal level and from the first dorsal interosseous (FDI) muscle of the dominant hand. Each subject completed two exercise protocols on a rowing ergometer: a light exercise protocol at a sub-maximal output for 10 min and an intense exercise protocol at maximum output for 1 min. A trial of ten magnetic stimuli was delivered before each of the protocols and, on finishing exercise, further trials of ten stimuli were delivered every 2 min for a 16 min period. Amplitudes of motor-evoked potentials (MEPs) in each of the three test muscles were measured before exercise and during the recovery period after exercise. The non-rowers showed a brief facilitation of MEPs in ES 2 min after light and intense exercise that was only present in the elite rowers after intense exercise. In the period 4-16 min after light exercise, the mean (+/- S.E.M.) MEP amplitude (relative to pre-exercise levels) was less depressed in the elite rowers (79.4 +/- 2.1%) than in the non-rowers (60.9 +/- 2.5%) in the left ES but not significantly so in the right ES. MEP amplitudes in FDI were significantly larger in the elite rowers, averaging 119.0 +/- 3.1% pre-exercise levels, compared with 101.2 +/- 5.8% in the non-rowers. Pre-exercise MEP latencies were no different in the two groups. After light exercise MEP latencies became longer in the elite rowers (left ES, 16.1 +/- 0.5 ms; right ES, 16.1 +/- 0.4 ms; dominant FDI, 23.4 +/- 0.2 ms) than in the non-rowers (left ES, 15.0 +/- 0.3 ms; right ES, 15.2 +/- 0.3 ms; dominant FDI, 21.5 +/- 0.2 ms). There were no differences in MEP depression or latency between elite rowers and non-rowers after intense exercise. We conclude that the smaller degree of MEP depression in the elite rowers after light exercise reflects less central fatigue within corticospinal control pathways than that seen in the non-rowers. The longer latency of MEPs seen in the elite rowers may reflect recruitment of more slower-conducting fatigue-resistant motor units compared with the non-rowers. These differences may be because the energy requirements for the non-rowers during light exercise are closer to their maximum capacity, leading to more fatigue. This notion is supported by the lack of any difference between groups following intense exercise when both groups were working at their own maximum.

Adult↗
PubMed1994

Passive tissues help the back muscles to generate extensor moments during lifting.

We examined the possibility that passive tissues can help the erector spinae to generate large extensor moments during lifting. One hundred and forty-nine healthy men and women participated in the study. Subjects pulled upwards with steadily increasing force on a floor-mounted load cell, while EMG activity was recorded from electrodes overlying the erector spinae at L3 and T10. Extensor moment was calculated from the load cell data, and was plotted against the full-wave rectified and averaged EMG signal. The relationship was linear with an intercept on the extensor moment axis (I) which indicated the flexion moment resisted by 'passive' (electrically silent) tissues. The dependence of I on lumbar flexion angle was studied by repeating the isometric pulls between 6 and 12 times, with the subject positioned in varying amounts of flexion, as measured by the '3-Space Isotrak'. Subjects then lifted weights of up to 20 kg from the floor, using 'stoop', 'squat' and 'freestyle' techniques, while lumbar flexion and EMG activity were recorded at 28 Hz. The isometric pulls showed that, on average, I increased from 25 Nm in lordotic postures to 120 Nm (for men) and 77 Nm (for women), in full flexion. During the lifts, peak extensor moment was generated with the lumbar spine flexed by 78-97% of the range between erect standing and full flexion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

Vestibulospinal and reticulospinal interactions in the activation of back muscle EMG in the rat.

The effects of electrical stimulation of the lateral vestibular nucleus (LVN) and medullary reticular formation (RF) on electromyographic activity in axial muscles medial longissimus (ML) and lateral longissimus (LL) in the rat were studied. Long trains (150-500 ms) at 200-330 Hz and 20-100 microA were sufficient to activate ML and LL at latencies of 20-100 ms from the beginning of the train. Results of stimulation at 200-330 Hz to RF or LVN showed that muscle units were activated at a fixed latency from any effective pulse in the stimulus train. Using high frequency (1 kHz) trains of 3-6 pulses to LVN, EMG activity was detected at minimum latencies of 3.5-6 ms. When conduction times from the medulla to the spinal cord, and the spinal cord to the muscle are subtracted, this latency range is consistent with monosynaptic activation. In many cases, muscle units were recruited in order of size, with both RF and LVN stimulation. Combined stimulation of LVN and RF sites in n. gigantocellularis led to EMG activity in ML and LL at currents which were insufficient to evoke activity when presented singly. When stimulation of one site (300-400 ms train) was just sufficient to evoke a response, a shorter, overlapping train (100-150 ms) to the other site led to a higher rate of muscle activity that continued through the end of the long train, even after the short train had ended. In all cases, the effect of RF facilitating LVN was similar to the effect of LVN facilitating RF. The evidence for convergence between these two systems in the medulla and the spinal cord is discussed.

Action Potentials↗
PubMed2002

Activation of back muscles during voluntary abduction of the contralateral arm in humans.

STUDY DESIGN: Motor-evoked responses to transcranial magnetic stimulation of the motor cortex were recorded from erector spinae and deltoid muscles while the arm was abducted voluntarily in 10 normal subjects. OBJECTIVE: To understand the neuronal substrate for the activation of the contralateral erector spinae muscle when the opposite arm is abducted. BACKGROUND DATA: When a standing individual abducts an arm, the center of gravity is altered; to avoid falling, trunk muscles become activated on the contralateral side. METHODS: Surface EMG activity was recorded from the right deltoid and left and right erector spinae muscles. Subjects maintained abduction of their right arm to 90 degrees at five different levels of isometric force in standing and lying postures. Transcranial magnetic stimulation was delivered to the motor cortex, producing motor-evoked responses in the three muscles during arm abduction and while relaxed. RESULTS: EMG activity in the left erector spinae increased with the force of right arm abduction in both postures. EMG levels in right erector spinae showed no consistent change with right arm abduction force. As arm abduction force was increased, motor-evoked responses were facilitated in deltoid and the left erector spinae but not the right erector spinae in both postures. The pattern of motor-evoked potential facilitation with arm abduction force tended to plateau between 50% and 70% maximum voluntary contraction in the deltoid, whereas it continued to climb more linearly in the left erector spinae. CONCLUSIONS: Facilitation of erector spinae with arm abduction remains evident in the lying posture when spinal postural stabilization mechanisms are presumably reduced. Similar facilitation profiles have been seen previously with changing voluntary activation of erector spinae in a trunk extension task, supporting the notion that during arm abduction the drive to the contralateral erector spinae has a corticospinal origin.

Adult↗
PubMed1995

New concept of spinal orthosis for weakened back muscles.

An anterior bending posture of the trunk during walking is often seen among the elderly commonly due to weakened thoraco-lumbar and gluteal muscles. For the management of this debilitating condition, the authors have developed a modified design of thoraco-lumbosacral orthosis (TLSO). Incorporated in this device are pockets for the accommodation of lead weights, which are located posteriorly at the level of the lumbar region and an elasticated anterior abdominal band. The results and level of patient acceptance achieved with the use of this brace have both been excellent.

Equipment Design↗