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At least 163 records · Page 9Linked to original sources
PubMed2004

Training can modify back muscle response to sudden trunk loading.

Sudden, unexpected loading to the trunk has been reported in the literature as a potential cause of low-back disorders. This study's aim was to investigate the effect of "readiness training" on the response to sudden back loading among untrained healthy individuals. The study included 19 participants and 19 matched controls. All were employees at the National Institute of Occupational Health. The participants received ten 45-min training sessions during a 4-week period. The training focused on reactions to a variety of expected and unexpected sudden trunk loadings, including balance and coordination exercises. Before and after the training, all subjects were tested for reaction to sudden trunk loading (SL). This entailed applying a horizontal force of 58 N to the subject's upper back. Elapsed time--measured between SL and stopping--decreased significantly in the training group (from 337 to 311 ms) compared with the control group. The improved stopping time was associated with a changed EMG signal, characterized by an increase in the early parts of the response (up to 225 ms) and a subsequent decrease. EMG onset latency was unaffected by training. This study is apparently one of the first to demonstrate that the response to sudden trunk loading can be improved in healthy subjects without an increase in pre-activation and associated trunk stiffness. In perspective, the results indicate a possibility for a training-induced reduction of the risk of low-back injuries, e.g., in nurses exposed to sudden trunk perturbations during patient handling.

Adult↗
PubMed1990

Ipsilateral and contralateral effects on cutaneous reflexes in a back muscle of the female rat: modulation by steroids relevant for reproductive behavior.

1. Multiunit EMG recordings of cutaneous reflexes--evoked in the back extensor, lateral longissimus (LL), by bilateral stimulation of nerves to dorsal flank skin--were studied in ovariectomized female rats with and without estrogen pretreatment. 2. Poststimulus time (PST) histograms of data from rats with and without estrogen pretreatment show that the axial EMG response (10-30 ms) to ipsilateral (ipsi) flank skin nerve stimulation is significantly shorter in latency (1.4 ms) and 67% larger than the response to contralateral (contra) flank skin nerve stimulation recorded at the same site (n = 29 pairs). 3. When late EMG responses were also evoked at 50-120 ms in 37% of ipsi and 29% of contra cutaneous reflexes, the incidence of multiunit activity in the late peak was significantly greater in rats pretreated with silastics containing 100% estradiol (E) compared with 10% E or cholesterol controls. 4. When an ipsi cutaneous reflex in LL was conditioned by a stimulus to the contra flank skin nerve at a condition-test interval of 30 ms (C-T 30 ms), the average number of discharges in the early peak of the histogram was double that in the histogram obtained from the unconditioned ipsi reflex, independent of estrogen pretreatment. 5. In 12 out of 19 cases in which a contra cutaneous reflex was conditioned by a stimulus to the ipsi flank skin nerve (C-T 30 ms), the number of discharges in the early peak of the histogram was less than that in the early peak of the histogram derived from the unconditioned contra response, independent of estrogen pretreatment. 6. Intravenous injections of progesterone (P) or its metabolite 5 alpha-pregnane-3 alpha-ol-20-one (tetrahydraprogesterone, THP) decreased the magnitude of the early peak of the ipsi cutaneous reflex and the contra cutaneous reflex in LL, independent of estrogen pretreatment. At the same time, it did not reduce the magnitude of the early peak evoked by either ipsi or contra nerves after conditioning from the other side at C-T 30 ms. 7. As a consequence, the percentage facilitation of ipsi cutaneous reflexes by contra cutaneous conditioning was significantly increased after P or THP. This suggests that these steroids can selectively enhance behaviors involving bilateral inputs. 8. An unchanged axial motoneuron pool output to bilateral cutaneous inputs after P and THP, in spite of reduced motoneuron responses to cutaneous inputs from each side of the body, implies an increased gain in the reflex circuit.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Significance of mat and shoe softness during prolonged work in upright position: based on measurements of low back muscle EMG, foot volume changes, discomfort and ground force reactions.

The aim of the investigation was to study the significance of mat and shoe softness during prolonged work in an upright position based on some physiological, biomechanical and comfort measurements related to the lower extremities and the low back. Eight healthy female volunteers performed 2 h of simulated standing and 2 h of standing/walking work tasks in the laboratory using four combinations of soft shoes, clogs, soft mat and concrete. Thus, each subject performed a total of eight 2 h work tests. The following parameters were measured pre-experimentally and one or more times during 2 h: total foot volume, vascular volume and interstitial volume of the left foot, EMG from the lumbar paraspinals, movement of centre of gravity (only during standing), biomechanical heel impact (only during standing/walking), perceived discomfort in lumbar back, legs and feet, whole body oxygen uptake, arterial blood pressure and heart rate. Using soft shoes rather than clogs during standing/walking work implies approximately a halving of the foot oedema formation and the heel impact. The effects due to the introduction of the soft mat are negligible. The local circulatory responses in the feet and the EMG-signs of paravertebral muscle fatigue are larger during standing compared to standing/walking work. The two investigated work types in this study differ regarding exposures as well as responses. Thus, it is recommended to shift between these postures and seated work during the working hours to improve job exposures.

Adult↗
PubMed1989

1989 Volvo Award in biomechanics. Mechanical recruitment of low-back muscles. Theoretical predictions and experimental validation.

A biomechanical model for studying lumbar muscle load sharing for a class of physical tasks that involve gravitational loading (holding weights) of the upper body in an erect posture is presented. The model assumes that the lumbar muscles balance the externally applied flexion and lateral bending moments. The concept of a 'loading plane' whose axes are the two bending moments is introduced. Any point in the plane can be viewed as a 'loading-point' describing a combination of bending moments that are applied to the body. The study of lumbar-muscle load sharing revealed loading conditions that required activation or deactivation of a particular muscle. The loading plane thus could be divided into regions of activity and inactivity for each muscle, separated by a 'switching curve.' The concept of 'switching curves' proved very useful for examining previously described physiologic assumptions on the loading conditions of particular muscle groups, and for grouping the 22 muscles described in the model into ten functional units. Electromyographic validation studies were conducted and showed a high degree of correlation between the model predictions and actual measurements for the contralateral (with respect to the load) muscles and to a lesser degree of correlation for the ipsilateral muscles.

Adult↗
PubMed2000

Evaluation of low back muscle surface EMG signals using wavelets.

OBJECTIVE: To compare the ability of observers to correctly detect the reaction time of erector spinae response to unexpected load by inspecting nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals and versus automatic detection on the same wavelet transformed signals. BACKGROUND: Traditionally, electromyographic signal analysis is performed using Fourier transform based methods. However, muscle response to transients such as unexpected load, have limitations when using these methods of electromyographic processing. DESIGN: A comparison was made of the three methods using the same signals attained during sudden loading of the trunk. METHODS: 11 chronic low back pain patients and eleven normal subjects were investigated in sudden loading. Surface electromyographic signals were obtained from the erector spine muscle at L3. The ability of observers to detect reaction time of erector spinae muscle responses of nonprocessed electromyographic signals versus inspection of wavelet transformed electromyographic signals versus an automatic peak detection program was determined. RESULTS: The results have shown that the spine muscle reaction time was easier and more accurately determined in the wavelet domain rather than in its original signal representation. CONCLUSION: Wavelet transform methods improved the analysis of electromyographic signals in the time domain by facilitating the determination of the time of muscle activity. RELEVANCE: Wavelet transform could be a valuable tool for electromyographic analysis in resolving the psychophysical problem of perception involved in the analysis of nonprocessed signals. In clinical environments, where the speed and the accuracy of the analysis of electromyographic signal is critical, the wavelet based signal processing could be very important.

Adult↗
PubMed1994

Lumbar paraspinal compartment pressure in back muscle exercise.

A paraspinal compartment pressure measurement was taken in 20 volunteers (a) to establish the normal compartment pressure in a series of body postures at rest and (b) to determine the difference in paraspinal compartment pressure during weight-lifting (40 pounds) exercise between straight back lifting and straight knee lifting. The measurement at rest showed a significant elevation of pressure in the sitting position compared with lying, standing, and bending positions. No significant difference in pressure was found between the two kinds of lifting exercises.

Adult↗
PubMed2004

Effects of experimentally induced pain and fear of pain on trunk coordination and back muscle activity during walking.

OBJECTIVE: To examine the effects of experimentally induced pain and fear of pain on trunk coordination and erector spinae EMG activity during gait. DESIGN: In 12 healthy subjects, hypertonic saline (acute pain) and isotonic saline (fear of pain) were injected into erector spinae muscle, and unpredictable electric shocks (fear of impending pain) were presented during treadmill walking at different velocities, while trunk kinematics and EMG were recorded. BACKGROUND: Chronic low back pain patients often have disturbed trunk coordination and enhanced erector spinae EMG while walking, which may either be due to the pain itself or to fear of pain, as is suggested by studies on both low back pain patients and healthy subjects. METHODS: The effects of the aforementioned pain-related manipulations on trunk coordination and EMG were examined. Results. Trunk kinematics was not affected by the manipulations. Induced pain led to an increase in EMG variability and induced fear of pain to a decrease in mean EMG amplitude during double stance. CONCLUSIONS: Induced pain and fear of pain have subtle effects on erector spinae EMG activity during walking while leaving the global pattern of EMG activity and trunk kinematics unaffected. This suggests that the altered gait observed in low back pain patients is probably a complex evolved consequence of a lasting pain, rather than a simple immediate effect. RELEVANCE: Variability of EMG data and kinematics may explain pain-dependent alterations of motor control, which in turn might contribute to a further understanding of the development of movement impairments in low back pain.

Adaptation, Physiological↗
PubMed1999

The activation of back muscles during locomotion in the developing rat.

The development of posture during locomotion was studied in rats from the 11th day until adulthood. The EMGs were recorded and analyzed of the left and right longissimus muscles at caudal, intermediate and rostral levels as well as of the gastrocnemius, the tibialis and the vastus medialis muscles and movements were simultaneously recorded on videotape. Results indicate that from the 12th day of life, burst activity occurs in the longissimus muscles which is phase-related to the stepcycle. Until the 21st day these muscles are most strongly activated during burst activity in the gastrocnemius muscle in the contralateral hindleg but thereafter this activation coincides with bursts in the ipsilateral gastrocnemius muscle. At adult age such activation in the LL is restricted to fast walking or to accelerations. Latencies between bursts in the longissimus muscles and the gastrocnemius muscles vary around 100 ms until the 25th day, but thereafter they decrease to adult values of less than 10 ms. The large variations in these phase-relations at all ages suggest that supraspinal influences and afferent input are important factors in this coupling. The shift from a contra- to an ipsilateral coupling between bursts in the longissimus and in the gastrocnemius muscles might indicate that an ontogenetically older pattern of locomotion with the trunk muscles playing a major role in propulsion, is replaced by a newer pattern, mainly effected by extremity movements.

Aging↗
PubMed2005

Differences in thoracic kyphosis and in back muscle strength in women with bone loss due to osteoporosis.

STUDY DESIGN: Cross-sectional. OBJECTIVES: To determine if thoracic kyphosis was different in older women grouped based on their bone mineral density (BMD) and back extensor strength (BES), and to determine if an association between and these variables exist. SUMMARY OF BACKGROUND DATA: Changes in kyphosis might be related to back extensor weakness in patients with osteoporosis. Disproportionate weakness in back extensor musculature considerably increases the possibility of deformities in the fragile osteoporotic spine. METHODS: A total of 189 female subjects 50 to 80 years of age were grouped by their BMD and additionally by their BES. All were evaluated for thoracic kyphosis, maximal isometric strength of the back extensors, and BMD of the lumbar spine and the hip. RESULTS: There was no significant difference in thoracic kyphosis among all groups. Multivariate analyses of BES and BMD showed that only BES might influence thoracic kyphosis (P = 0.02). There was no correlation between BES and BMD. Statistically significant deficit in BES was observed only between the osteoporotic and osteopenic group (P < 0.05). The importance of BES in maintaining posture was observed when the study population was divided according to their BES level. With respect to thoracic kyphosis and BMD values, there were no statistical differences between strong women (BES more than 60 N) and those with medium BES (BES between 60 and 35 N). But the weakest group (BES less then 35 N) had significantly higher (P < 0.05) mean values of thoracic kyphosis in comparison to strong women (BES more than 60 N) and those with medium BES (BES between 60 and 35 N). CONCLUSION: The severity of thoracic kyphosis may be influenced especially by changes in BES. Therefore, provision of strong, natural extrinsic support for the spine seems to be important to decrease the incidence of spinal deformity.

Aged↗
PubMed2005

Improved evaluation of back muscle SEMG characteristics by modelling.

Surface EMG (SEMG) as non-invasive method is a valuable tool in functional studies of movement co-ordination. The interpolation of the SEMG power (EMG mapping) gives information about intra- and inter-muscular co-ordination. It has been shown that SEMG maps of low back pain patients and healthy subjects differ. The only major drawback to SEMG is that volume conduction of muscle tissue, fat, and skin decreases the spatial and temporal resolution of signals. To improve the interpretation of SEMG signals, we have applied high pass filtering of cross covariance functions, which has proved to be useful in increasing the spatial resolution, to SEMG data of the back region. Experimental data demonstrate that SEMG signals from the back extensors show only rarely signs of action potential propagation. This behaviour, also described in the literature, can be explained by a model assuming short, deep muscle fibres, having bipolar end effects, with overlapping positions parallel to the fibre direction. This condition is fulfilled by the mm. multifidii et rotatores which are part of the m. erector spinae. Although the model is simplistic, the agreement between simulations and experiments is good.

Journal Article↗
PubMed1984

Detection of stimulated back muscle contractions by moiré topography.

The ability to treat scoliosis via surface stimulated trunk muscle contractions is now being evaluated at several treatment centers. In order to make biomechanical analysis of the procedure, so that the technique can be used optimally, data are needed to quantify the muscle contractions and structural changes by different electrode locations. This paper presents the use of a modified shadow moiré technique to quantify geometric changes resulting from electrical stimulation applied to the surface of the back in a healthy subject.

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