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At least 1,783 records · Page 99Linked to original sources
PubMed2006

Lumbosacral orthoses reduce trunk muscle activity in a postural control task.

Biomechanical modeling estimated that trunk muscle activity during various tasks could be reduced by 1-14% without the loss of spine stability when a lumbosacral orthosis (LSO) is worn [Cholewicki, J., 2004. The effects of lumbosacral orthoses on spine stability: what changes in EMG can be expected? Journal of Orthopedic Research 22, 1150-1155]. The present study experimentally tested these theoretical predictions in an unstable sitting task. This task required subjects to balance on a seat supported by a plastic hemisphere (slashed circle=30cm) and placed on a force plate that tracked the center of pressure (CoP). The average CoP velocity quantified subjects' performance. Healthy subjects (12 males, 11 females) balanced for 20s in 3 trials performed with and without the LSO in random order. EMG was recorded bilaterally from rectus abdominis (RA), external oblique (EO), thoracic (TES) and lumbar erector spinae (LES), and expressed as the % of maximum voluntary activation (%MVA). There was no difference in the balance performance with and without the LSO (p=0.13). However, EMG averaged across the trials was significantly lower in the LSO, as compared to the No LSO condition, for TES (5.8+/-3.2 vs. 6.4+/-3.7%MVA, p=0.02) and LES (3.7+/-1.5 vs. 5.9+/-3.9%MVA, p=0.01). No significant differences were present in the abdominal muscle activity. These results agree with earlier spine modeling simulations, which predicted the greatest reduction in muscle activity due to LSO to occur in TES and LES. It was hypothesized that such a reduction in muscle co-contraction could benefit patients with low back pain, who exhibit elevated muscular activity during postural tasks such as walking, standing and sitting.

Abdominal Muscles↗
PubMed1992

Decrease in back strength in asymmetric trunk postures.

The extension force against resistance was recorded in 23 postures for 12 subjects to find explanations for the decrease in back strength in asymmetric postures. A reduction in muscle force in asymmetric postures was found up to 40%, but was strongly dependent on the plane in which asymmetry occurred, and on the posture to which it referred. A quantitative relationship between the forces exerted in different asymmetric postures is discussed, as a basis for formulating universal ergonomic guidelines for optimal working postures. The reduction in force in different asymmetric postures can be explained by length of the muscle, the activation of the muscle, and the moment angle of the muscle.

Adult↗
PubMed2002

Latency, duration and dose response relationships of amino acid effects on human muscle protein synthesis.

The components of the stimulatory effect of food on net deposition of protein are beginning to be identified and separated. One of the most important of these appears to be the effect of amino acids per se in stimulating muscle anabolism. Amino acids appear to have a linear stimulatory effect within the range of normal diurnal plasma concentrations from postabsorptive to postprandial. Within this range, muscle protein synthesis (measured by incorporation of stable isotope tracers of amino acids into biopsied muscle protein) appears to be stimulated approximately twofold; however, little further increase occurs when very high concentrations of amino acids (>2.5 times the normal postabsorptive plasma concentration) are made available. Amino acids provided in surfeit of the ability of the system to synthesize protein are disposed of by oxidation, ureagenesis and gluconeogenesis. The stimulatory effect of amino acids appears to be time dependent; a square wave increase in the availability of amino acids causes muscle protein synthesis to be stimulated and to fall back to basal values, despite continued amino acid availability. The relationship between muscle protein synthesis and insulin availability suggests that most of the stimulatory effects occur at low insulin concentrations, with large increases having no effect. These findings may have implications for our understanding of the body's requirements for protein. The maximal capacity for storage of amino acids as muscle protein probably sets an upper value on the extent to which amino acids can be stored after a single meal.

Amino Acids↗
PubMed1990

[Evaluation of thiocolchicoside as monotherapy in low back pain. Results of a randomized study versus placebo].

Thiocolchicoside is a muscle relaxant which, due to its mainly spinal GABA-agonist activity, is used by the oral and intramuscular routes in the ambulatory treatment of painful contracture of the skeletal muscles. The effectiveness and acceptability of this drug in the treatment of acute low-back pain were evaluated in a multicentre, randomized, double-blind, drug versus placebo trial involving 98 patients. The effectiveness of thiocolchicoside was assessed on the following criteria: patients' overall opinion, pain intensity, number of analgesic tablets taken, vertebral rigidity and ability to resume ordinary daily tasks. The results obtained showed that thiocolchicoside significantly improves the principal criterion by the second day of treatment and the other criteria within 5 days.

Adult↗
PubMed1994

Anthropometric variables, self-efficacy beliefs, and pain and disability ratings on the isokinetic performance of low back pain patients.

OBJECTIVES: This study investigated how age, sex, height, body weight, self-efficacy beliefs, pain, and subjective disability predict the performance of low back pain patients on an isokinetic trunk muscle test. METHODS: One hundred and five patients participated in the study. Dependent variables were isokinetic flexion and extension strength measured as total work done at speeds 50, 100, and 150 degrees/second. RESULTS: The anthropometric measures were poor predictors, height being the only significant one. Body weight and age were of no relevance for the performance. Subjective pain and disability had negative effects on the performance of men, but not of women. Self-efficacy beliefs, i.e., the patient's belief in his or her capability to endure physical activities, was the most powerful predictor. CONCLUSION: For the purpose of validation, standardization, and interpretation of isokinetic performance in low back pain patients, these factors should be taken into account.

Adult↗
PubMedDate not supplied

Muscular function in chronic low-back dysfunction.

The purpose of this study was to use electromyography to determine the level and pattern of muscle activity of the rectus abdominus and T10, L1, and L3 erector spinae muscle in healthy subjects and patients with chronic low-back dysfunction during various postures and activities. Statistically significant differences in erector spinae activities were found between groups for the Valsalva maneuver and for portions of the sit-up exercise. Comparisons between the 4.5-kg and 16-kg lifts completed with bent and straight knees showed few differences during actual lifts, but the patients with chronic dysfunction maintained an increased level of activity when lifts had been completed.

Adult↗
PubMed2001

Spinal manipulation causes variable spine kinematic and trunk muscle electromyographic responses.

STUDY DESIGN: Analytic cohort with a convenience sample in a research clinic. OBJECTIVES: To determine the influence of a spinal manipulation on trunk kinematics and associated trunk myoelectric activity. SUMMARY OF BACKGROUND: While the mechanism of spinal manipulation is unknown, it has been theorized to influence spinal range of motion and trunk muscle activity. METHODS: Trunk kinematics were measured in low back pain patients (n = 14) during simple range of motion tasks in three planes, while trunk muscle electromyogram signals were recorded bilaterally from paraspinal and abdominal musculature. Kinematics and electromyogram signals were assessed pre-post manipulation. Electromyogram activity was also assessed pre-post manipulation during quiet stance. RESULTS: While no consistent kinematic or electromyographic changes occurred following manipulation across the population, individual changes were observed. The largest changes (> 6 degrees ) in range of motion occurred in the sagittal plane of three patients experiencing the greatest amount of pain. During quiet stance 17 muscles across all subjects exhibited changes in muscle activity following manipulation. Sixteen of those changes were decreases in muscle amplitude. CONCLUSIONS: This study offers some preliminary data on the short-term effects of manipulation on lumbar range of motion and dynamic electromyogram. The findings suggest that the response to manipulation is variable and dependent on the individual, with no change in some to the largest changes seen in the more pained patients. Relevance. Basic science investigations into the mechanisms and biomechanical influences of spinal manipulation are few. This study attempts to address issues of measureable functional change with manipulative therapy.

Adult↗
PubMed1989

Proteolytic enzyme activities in skeletal muscle of high jumping rats.

Physical activity can be studied by various kind of exercises. Many works have been published in field of proteolytic enzyme activities in skeletal muscle during endurance training. In this work we used high jumping as a dynamic force velocity training to study the changes in proteolytic enzyme activities during this type of exercise. The activity of cathepsin D, cathepsin L and ATN-ase (Acetyl-Tyrosine-paranitroanilide-splitting enzyme) in vastus lateralis muscle was measured after one, 3, 7 or 11 weeks of high jumping exercise. The results demonstrated that proteinase activity began to increase when the load, i.e. number of jumping and the weight put on the rat's back was too much for their muscles. They could carry out the task consuming the energy originating from muscle tissue in the first period of the experiment, but in the second period (after 7 weeks) the type of training with this load became equal with an endurance training.

Animals↗
PubMed1979

An analysis of the inhibitory post-synaptic current in the voltage-clamped crayfish muscle.

1. Inhibitory post-synaptic currents (i.p.c.s) were recorded from the feed-back current through a wire electrode inserted longitudinally into the opener muscle fibre of the claw in the crayfish (Cambarus clarkii). 2. I.p.s.c. rose to its peak in about 3-4 msec and decayed approximately exponentially. The decay time constant at -100 mV was 9.4 msec. 3. The decay time constant decreased as the membrane was hyperpolarized and increased during depolarization. The time constant (tau) depends on voltage (V) according to the relation tau = a exp (AV), with a = 18.6 msec and A = 0.0065 mV-1. Voltage dependence was opposite in direction to that seen at frog end-plates, but in the same direction as that of e.p.s.c. in crayfish muscle. 4. At lower temperatures, the rise and fall times of i.p.s.c.s were prolonged. Q10 for the decay time constant was 2.4 between 22.6 and 12.5 degrees C. 5. When pH was decreased from 7.2 to 5.5, the decay time constant increased by about 50%, with little change in the voltage dependence of the time course. 6. When chloride in the solution was changed to iodide, the decay time constant was increased by a factor of 3, while voltage dependence of the time course was not changed. In bromide solution the decay time constant increased by about 50%. 7. Peak amplitudes of i.p.s.c.s were approximately linear as the membrane was depolarized, but they levelled off as the membrane was hyperpolarized beyond reversal potential. The non-linear I-V relation did not result from inadequate voltage clamping, nor from a change in the inside concentration of chloride. After equilibration with iodide solution the I-V relation was approximately linear. 8. The decay time constant was increased after repetitive nerve stimulation. This prolongation became more pronounced at lower temperatures. 9. The kinetic process of the transmitter action is discussed. It is suggested that the rate limiting process for i.p.s.c. is binding and unbinding of the transmitter to the receptor.

Animals↗
PubMed1997

Ear projection and the posterior auricular muscle insertion.

Prominent ears is a common congenital anomaly affecting approximately 5 percent of the general population. The etiology has been attributed to three basic deformities in the ear structure: valgus of the concha with a cranioauricular angle greater than 40 degrees, underfolding of the anthelix, and rarely, hypertrophy of the concha. It is believed that by virtue of its insertion onto the ponticulus, the cranial surface of the concha, the posterior auricular muscle may function to pull the auricle back toward the head. A proximally (anteromedially) displaced insertion site would decrease the length of the effective momentum of the muscle, leading to protrusion of the auricle. This study was conducted to determine if indeed a relationship between the posterior muscle insertion site and ear projection could be established clinically by measuring these parameters intraoperatively in patients presenting for otoplasty and in patients without prominent ears who required conchal cartilage grafts for other procedures.

Adolescent↗
PubMed2002

The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles.

The purpose of this study was to measure the relative contributions of 4 hip and thigh muscles while performing squats at 3 depths. Ten experienced lifters performed randomized trials of squats at partial, parallel, and full depths, using 100-125% of body weight as resistance. Electromyographic (EMG) surface electrodes were placed on the vastus medialis (VMO), the vastus lateralis, (VL), the biceps femoris (BF), and the gluteus maximus (GM). EMG data were quantified by integration and expressed as a percentage of the total electrical activity of the 4 muscles. Analysis of variance (ANOVA) and Tukey post hoc tests indicated a significant difference (p < 0.001*, p = 0.056**) in the relative contribution of the GM during the concentric phases among the partial- (16.9%*), parallel- (28.0%**), and full-depth (35.4%*) squats. There were no significant differences between the relative contributions of the BF, the VMO, and the VL at different squatting depths during this phase. The results suggest that the GM, rather than the BF, the VMO, or the VL, becomes more active in concentric contraction as squat depth increases.

Electromyography↗
PubMed1997

Characterization of troponin-C interactions in skinned barnacle muscle: comparison with troponin-C from rabbit striated muscle.

Previously it was shown that when troponin-C (TnC) is extracted from barnacle myofibrillar bundles they lose their Ca2+ sensitivity, which can be restored by adding back barnacle TnC (either isoform, BTnC1 or BTnC2). Thus barnacle muscle shows thin filament regulation, as does rabbit psoas skeletal muscle. In this paper we compare the interactions of barnacle and rabbit fast muscle TnC in their respective muscles. We demonstrate that muscle fibres from the giant barnacle, Balanus nubilus, contain about 186 microM kg-1 muscle tissue of BTnC1 plus BTnC2 compared to about 91 microM kg-1 of TnC in rabbit psoas muscle fibres. Extraction of BTnC is achieved using similar low ionic strength, low divalent ion Ca(2+)-low Mg2+ conditions which are required for TnC extraction in rabbit psoas skinned muscle fibres; extraction was prevented by 1 mM Mg2+. Full reconstitution of Ca(2+)-sensitivity was achieved by adding back BTnC (1 + 2, or 2). Reconstitution of barnacle muscle with rabbit fast skeletal TnC (RTnC) was more complex, with partial recovery of Ca(2+)-sensitivity with reconstitution in the presence of 3 mM Mg2+ and more fully with reconstitution in the presence of activating Ca2+ (pCa 4.0). This suggests that the barnacle TnC-TnI (troponin I) recognition sites may be more complex than in rabbit because the barnacle sites appear to have at least two different conformations or types, in which one recognizes RTnC in the presence of Mg2+ and the other only in the presence of Ca2+ and Mg2+. This is consistent with the presence of several TnI isoforms in barnacle striated myofibrils. RTnC has two C-terminal Ca(2+)-Mg2+ binding sites that are thought to be involved in the Mg(2+)-sensitive binding of RTnC in rabbit muscle, yet it has been suggested that this site in barnacle muscle does not bind Mg2+, even though Mg2+ stabilizes BTnC binding in barnacle muscle. Consistent with this stabilizing action of Mg2+, using fluorescent probes IAANS or IAE on isolated BTnC2 we demonstrate that BTnC2 binds both Ca2+ and Mg2+, but the data do not suggest direct competition. Consistent with the C-terminal sites on BTnC being Ca(2+)-specific, BTnC1 + 2 could only reconstitute low levels of force (about 1/3) in TnC-extracted rabbit skinned muscle fibers in the presence of pCa 4.0 (not just Mg2+) and only at low ionic strengths (0.09 M). Ca(2+)-activation of contraction was further examined using fluorescently labelled BTnC2 (labelled with IANBD) incorporated into skinned barnacle myofibrillar bundles. Maximal Ca2+ binding produced structural changes in BTnC which resulted in a 45% decrease in the fluorescence compared to the value at pCa 9.2. The magnitude of the fluorescence decrease paralleled the increase in force with increasing Ca2+. The Hill fits to the data gave pCa1/2 and n of 5.61 +/- 0.02 and 2.06 +/- 0.12 for force, and 5.52 +/- 0.02 and 1.88 +/- 0.10 for fluorescence. Removing MgATP to induce rigor in the fibre decreased BTnC2-NBD fluorescence only about 11%, but the addition of Ca2+ in rigor further decreased the fluorescence to a slightly larger extent than under maximal Ca2+ activating conditions. These fluorescence changes are qualitatively similar to the fluorescence enhancement seen with Ca(2+)-activation and rigor with RTnCDanz exchanged into rabbit psoas skinned muscle fibres. The data support a similar model for Ca(2+)-activation of force in barnacle muscle and in rabbit psoas skeletal muscle fibres.

Animals↗
PubMed1997

Dynamic testing of the motor stereotype in prone hip extension from neutral position.

OBJECTIVE: The purpose of the study was to identify a sequential activation of lumbar and hip muscles in active prone hip extension from neutral position in subjects without a history of low back pain. DESIGN: Using surface electromyography, the myoelectric activity onsets of agonistic and antagonistic hip muscles were recorded. BACKGROUND: The development of low back pain is ascribed to changes of the muscle firing order in prone hip extension. There appeared to be no normative data on muscle firing order of the lumbar and hip musculature to provide a basis for recognizing variations. METHODS: Fifteen healthy subjects performed standardized right hip extensions. Time-normalized onset of EMG activity in each muscle was measured for each trial. RESULTS: A MANOVA revealed significant (P < 0.01) differences between the activity onsets of synergistic muscles in hip extension. CONCLUSIONS: On the results it was concluded that the consistent muscle firing order of ipsilateral lumbar erector spinae, semitendinosus, contralateral lumbar erector spinae, tensor fasciae latae, and gluteus maximus demonstrate the characteristic pattern in prone hip extension. In future studies it is essential to evaluate also the hip extension pattern in functional upright conditions during gait and their relationship to spinal mechanics.

Journal Article↗
PubMed1990

The relief of low back pain with the WARP abdominoplasty: a preliminary report.

The alleviation of back pain in 24 of 25 patients who previously had chronic, persistent pain is reported following wide abdominal rectus plication (WARP) abdominoplasty. Radiographic evidence of increases in intervertebral space as well as MRI evidence of possible disk reconstitution are presented. Muscle strength evaluation demonstrates a significant increase in transverse abdominis-internal oblique complex strength with only surgery and no rehabilitative therapy. Intraperitoneal and lower extremity venous pressure changes are discussed, as are complications. A classification of abdomen groups 0 to 4 is presented. The abdominal pressure test and suggested appropriate patient selection are critical to successful treatment.

Abdominal Muscles↗
PubMed1977

Re-innervation of fast and slow twitch muscle following nerve crush at birth.

1. The frequency of miniature end-plate potentials (m.e.p.p.s) was significantly greater in the fast twitch extensor digitorum longus muscle (extensor) than in the slow twitch soleus, even though end-plate surface area was greater for fibres in the latter muscle. 2. Crush of the sciatic nerve at birth did not prevent the appearance of this difference in m.e.p.p. frequency. However, the frequency of the potentials in the re-innervated muscles was less than normal, even though the regenerated neuromuscular junction was qualitatively normal in morphology. 3. Though the re-innevated muscles were differentiated with respect to twitch time course, the extensor muscle was more responsive than normal to the contracture-inducing action of caffeine. 4. The Z line of the re-innervated extensor muscle was similar to that of the normal soleus in thickness. 5. Resting potential, passive electrical properties and action potential generating mechanism of the sarcolemma were normal. 6. Since the re-innervated muscles lacked muscle spindles, a role of sensory feed-back in the function of the neuromuscular junction as well as the neutrotrophic regulation of muscle is discussed.

Action Potentials↗
PubMed1981

Histochemical changes of rat skeletal muscles induced by cold acclimation.

After cold acclimation of rats the augmentation of succinic dehydrogenase activity in the fast-twitch oxidative glycolytic (FOG) and the slow-twitch oxidative (SO) fibers was observed in entire regions of the soleus, the extensor digitorum longus, the plantaris, the longissimus and the gastrocnemius muscles. Furthermore, a tendency to increased proportion of the FOG and the SO fibers was observed more prominently in superficial regions than in deep regions of a large muscle such as the gastrocnemius muscle.

Adaptation, Physiological↗