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PubMed1999

Physiological response to submaximal isometric contractions of the paravertebral muscles.

STUDY DESIGN: Brief (30-second) isometric trunk extensions at 5%, 20%, 40%, 60%, and 80% of maximal voluntary contraction (MVC) and 3 minutes of prolonged trunk extension (20% MVC) in erect position were studied in nine healthy male subjects. OBJECTIVES: To investigate the intercorrelation between intramuscular pressure and tissue oxygenation of the paravertebral muscles during submaximal isometric contractions and further, to evaluate paravertebral electromyogram and intramuscular pressure as indicators of force development. SUMMARY OF BACKGROUND DATA: Local physiologic responses to muscle contraction are incompletely understood. METHODS: Relative oxygenation was monitored with noninvasive near-infrared spectroscopy, intramuscular pressure was measured with a transducer-tipped catheter, and surface electromyogram was monitored at three recording sites. RESULTS: The root mean square amplitudes of the paravertebral electromyogram (L4, left and right; T12, right) and intramuscular pressure measured in the lumbar multifidus muscle at L4 increased with greater force development in a curvilinear manner. A significant decrease in the oxygenation of the lumbar paravertebral muscle in response to muscle contraction was found at an initial contraction level of 20% MVC. This corresponded to a paravertebral intramuscular pressure of 30-40 mm Hg. However, during prolonged trunk extension, no further decrease in tissue oxygenation was found compared with the tissue oxygenation level at the end of the brief contractions, indicating that homeostatic adjustments (mean blood pressure and heart rate) over time were sufficient to maintain paravertebral muscle oxygen levels. CONCLUSION: At a threshold intramuscular pressure of 30-40 mm Hg during muscle contraction, oxygenation in the paravertebral muscles is significantly reduced. The effect of further increase in intramuscular pressure on tissue oxygenation over time may be compensated for by an increase in blood pressure and heart rate. Surface electromyogram amplitudes and intramuscular pressure can be used as indicators of paravertebral muscle force.

Adult↗
PubMed2000

The role of paraspinal muscle spindles in lumbosacral position sense in individuals with and without low back pain.

STUDY DESIGN: A two-group experimental design with repeated measures on one factor was used. OBJECTIVES: To investigate the role of paraspinal muscle spindles in lumbosacral position sense in individuals with and without low back pain. SUMMARY OF BACKGROUND DATA: Proprioceptive deficits have been identified in patients with low back pain. The underlying mechanisms, however, are not well documented. METHODS: Lumbosacral position sense was determined before, during, and after lumbar paraspinal muscle vibration in 23 young patients with low back pain and in 21 control subjects. Position sense was estimated by calculating the mean absolute error, constant error, and variable error between six criterion and reproduction sacral tilt angles. RESULTS: Repositioning accuracy was significantly lower in the patient group than in healthy individuals (absolute error difference between groups = 2.7 degrees, P < 0.0001). Multifidus muscle vibration induced a significant muscle-lengthening illusion that resulted in an undershooting of the target position in healthy individuals (constant error = -3.1 degrees, P < 0.0001). Conversely, the position sense scores of the patient group did not display an increase in negative directional error but a significant improvement in position sense during muscle vibration (P < 0.05). No significant differences in absolute error were found between the first and last trial in the healthy individuals (P >/= 0.05) and in the patient group (P > 0.05). CONCLUSIONS: Patients with low back pain have a less refined position sense than healthy individuals, possibly because of an altered paraspinal muscle spindle afference and central processing of this sensory input. Furthermore, muscle vibration can be an interesting expedient for improving proprioception and enhancing local muscle control.

Adolescent↗
PubMed2000

Decrease in trunk muscular response to perturbation with preactivation of lumbar spinal musculature.

STUDY DESIGN: An experimental study of healthy subjects' trunk muscle responses to force perturbations at differing angles and steady state efforts. OBJECTIVES: To determine whether increased preactivation of muscles was associated with decreased likelihood of muscular activation in response to a transient force perturbation. SUMMARY OF BACKGROUND DATA: Trunk stability (ability to return to equilibrium position after a perturbation) requires the stiffness of appropriately activated muscles to prevent buckling and consequent "self-injury." Therefore, greater trunk muscle preactivation might decrease the likelihood of reflex muscle responses to small perturbations. METHODS: Each of 13 subjects stood in an apparatus with the pelvis immobilized. A harness around the thorax provided a preload and a force perturbation by a horizontal cable and a movable pulley attached to one of five anchorage points on a wall track surrounding the subject at angles of 0 degrees, 45 degrees, 90 degrees, 135 degrees, and 180 degrees to the forward direction. Subjects first equilibrated with a preload effort of nominally 20% or 40% of their maximum extension effort. Then a single full sine-wave force perturbation pulse of nominal amplitude, 7.5% or 15% of maximum effort, duration 80 milliseconds or 300 milliseconds, was applied at a random time, with three repeated trials of each test condition. The applied force (via a load cell) and the electromyographic activity of six right and left pairs of trunk muscles were recorded. Muscle responses were detected by two methods. 1) Shewhart method: electromyographic signal greater than "baseline" values by more than three standard deviations, and 2) Mean Electromyographic Difference method: mean electromyographic signal in a time window 25 to 150 milliseconds after the force perturbation greater than that in a 25- to 150-millisecond window before the perturbation. RESULTS: Lower preload efforts were associated with more muscle responses (overall mean response detection rate = 33% at low preload and 25% at high preload). Using the Shewhart method, there were significant differences by effort (P<0.05) for all abdominal muscles and for all left dorsal muscles except multifidus. Using the Mean Electromyographic Difference method, there were significant differences by effort (P<0.05) for the same dorsal muscles, but only for one of the abdominal muscles. CONCLUSIONS: Findings are consistent with the hypothesis that the spine can be stabilized by the stiffness of activated muscles, obviating the need for active muscle responses to perturbations.

Adult↗
PubMed2000

Fos expression in the rat brain and spinal cord evoked by noxious stimulation to low back muscle and skin.

STUDY DESIGN: Acute noxious stimulation delivered to lumbar muscles and skin of rats was used to study Fos expression patterns in the brain and spinal cord. OBJECTIVES: The present study was conducted to determine the differences in Fos expression in the brain and spinal cord as evoked by stimuli delivered to lumbar muscles and skin in rats. SUMMARY OF BACKGROUND DATA: Patients with low back pain sometimes show psychological symptoms, such as quiescence, loss of interest, decreased activities, appetite loss, and restlessness. The pathway of deep somatic pain to the brain has been reported to be different from that of cutaneous pain. However, Fos expression has not been studied in the central nervous systems after stimulation of low back muscles. METHODS: Rats were injected with 100 L of 5% formalin into the multifidus muscle (deep pain group; n = 10) and into the back skin of the L5 dermatome (cutaneous pain group; n = 10). Two hours after injection, the distribution of Fos-immunoreactive neurons was studied in the brain and spinal cord. RESULTS: Fos-immunoreactive neurons were observed in laminae I-V in the spinal cord in the cutaneous pain group, but they were not seen in lamina II in the deep pain group. In the brain, Fos-immunoreactive neurons were significantly more numerous in the deep pain group than in the cutaneous pain group in the piriform cortex, the accumbens nucleus core, the basolateral nucleus of amygdala, the paraventricular hypothalamic nucleus, the ventral tegmental area, and the ventrolateral periaqueductal gray. CONCLUSION: The finding that Fos-immunoreactive neurons were absent from lamina II of the spinal cord in the deep pain group is similar to that of the projection pattern of the visceral pain pathway. Fos expression in the ventrolateral periaqueductal gray in the deep pain group may represent a reaction of quiescence and a loss of interest, activities, or appetite. Furthermore, the detection of large numbers of Fos-immunoreactive neurons in the core of accumbens nucleus, basolateral nucleus of amygdala, paraventricular hypothalamic nucleus, and ventral tegmental area in the deep pain group may suggest a dominant reaction of dopaminergic neurons to stress, and a different information processing pathway than from that of cutaneous pain.

Animals↗
PubMed2001

A functional subdivision of hip, abdominal, and back muscles during asymmetric lifting.

STUDY DESIGN: An experimental study of muscle recruitment patterns during asymmetric lifting in healthy individuals. OBJECTIVE: To investigate muscle recruitment patterns during asymmetric lifting, representing a common daily living activity, to determine whether systematic differences exist between functioning of the local and global muscle systems. SUMMARY OF BACKGROUND DATA: The normal function of the local muscle system is to provide sufficient segmental stability to the spine. The global muscle system provides general trunk stabilization and enables the static and dynamic work necessary for daily living and sports activities. Current knowledge about these two muscle groups appears to be specifically derived from anatomic findings and experiments conducted under artificial circumstances. To the authors' knowledge, the recruitment patterns of both muscle groups have not been investigated in daily living activities. METHODS: Twenty-nine healthy individuals performed different variants of asymmetric lifting activities. Electromyographic data were collected from seven hip, abdominal, and back muscle pairs. In addition, trunk kinematics were measured by means of an ultrasonic movement analysis system. RESULTS: The left and right obliquus internus, rectus femoris, and multifidus showed symmetric co-contraction in all variants of activities. In contrast, significant left/right differences were observed in the external oblique, gluteus maximus, iliocostalis lumborum pars thoracis, and latissimus dorsi. CONCLUSIONS: The results of this study show a symmetric activation of the local muscles during the performance of low-load, asymmetric lifting tasks, which suggests that these muscles play a stabilizing role during these manoeuvres. The global muscles, however, hand show asymmetric patterns of activation during the same tasks, supporting their role as global stabilizers and prime movers.

Abdominal Muscles↗
PubMed2002

The relation between the transversus abdominis muscles, sacroiliac joint mechanics, and low back pain.

STUDY DESIGN: Two abdominal muscle patterns were tested in the same group of individuals, and their effects were compared in relation to sacroiliac joint laxity. One pattern was contraction of the transversus abdominis, independently of the other abdominals; the other was a bracing action that used all the lateral abdominal muscles. OBJECTIVES: To demonstrate the biomechanical effect of the exercise for the transversus abdominis known to be effective in low back pain. SUMMARY OF BACKGROUND DATA: Drawing in the abdominal wall is a specific exercise for the transversus abdominis muscle (in cocontraction with the multifidus), which is used in the treatment of back pain. Clinical effectiveness has been demonstrated to be a reduction of 3-year recurrence from 75% to 35%. To the authors' best knowledge, there is not yet in vivo proof of the biomechanical effect of this specific exercise. This study of a biomechanical model on the mechanics of the sacroiliac joint, however, predicted a significant effect of transversus abdominis muscle force. METHODS: Thirteen healthy individuals who could perform the test patterns were included. Sacroiliac joint laxity values were recorded with study participants in the prone position during the two abdominal muscle patterns. The values were recorded by means of Doppler imaging of vibrations. Simultaneous electromyographic recordings and ultrasound imaging were used to verify the two muscle patterns. RESULTS: The range of sacroiliac joint laxity values observed in this study was comparable with levels found in earlier studies of healthy individuals. These values decreased significantly in all individuals during both muscle patterns (P < 0.001). The independent transversus abdominis contraction decreased sacroiliac joint laxity (or rather increased sacroiliac joint stiffness) to a significantly greater degree than the general abdominal exercise pattern (P < 0.0260). CONCLUSIONS: Contraction of the transversus abdominis significantly decreases the laxity of the sacroiliac joint. This decrease in laxity is larger than that caused by a bracing action using all the lateral abdominal muscles. These findings are in line with the authors' biomechanical model predictions and support the use of independent transversus abdominis contractions for the treatment of low back pain.

Abdomen↗
PubMed2002

Diverging intramuscular activity patterns in back and abdominal muscles during trunk rotation.

STUDY DESIGN: An intramuscular electromyographic study was performed on trunk rotations during sitting and standing. OBJECTIVE: The aim was to provide new information on activation levels for deep trunk muscles in various unresisted and resisted trunk rotations. SUMMARY AND BACKGROUND DATA: Frequent daily trunk twisting and decreased maximal strength during trunk rotation have been associated with low back pain or sciatic pain. However, the involvement of deep trunk muscles during different trunk rotations is relatively unknown. METHODS: Ten healthy subjects participated. Fine-wire electrodes were inserted, under ultrasound guidance, into psoas, quadratus lumborum, the superficial medial lumbar erector spinae (ES-s, multifidus) and its deep lateral portion (ES-d, iliocostalis), iliacus, rectus abdominis, obliquus externus, and obliquus internus. RESULTS: The highest involvement for all muscles was observed on the ipsilateral side, in maximal trunk twists with shoulder resistance, except obliquus externus, which showed a dominant contralateral side, and rectus abdominis, which was little activated in all rotations. In contrast, maximal trunk twist without shoulder resistance, i.e., freely performed, resulted generally in lower levels for all muscles involved and in a shift of side dominance for the lumbar muscles quadratus lumborum, psoas, and ES-s. CONCLUSIONS: During trunk rotations the activity patterns for various trunk muscles could drastically change, and even be the opposite, between the two body sides, within the same type of task, depending on several factors such as initial position, effort level, sitting or standing, and external shoulder resistance.

Abdomen↗
PubMed2002

The impact of self-retaining retractors on the paraspinal muscles during posterior spinal surgery.

STUDY DESIGN: This was a prospective pilot study examining pre-, intra- and postoperative measures. OBJECTIVES: The aim of the study was to investigate the effect of muscle retractors on the posterior spinal muscles during posterior spinal surgery. SUMMARY OF BACKGROUND DATA: Previous studies have identified changes in the structure and function of the back extensor mechanism as a result of low back pain. However, the effect of surgery on the functioning of these muscles, particularly surgical retraction, has received less attention. METHODS: Twenty patients undergoing posterior spinal surgery were recruited into this study, and recordings of intramuscular pressure during surgery were performed using a pressure-monitoring system before insertion of retractors, 5, 30, and 60 minutes into surgery, and on removal of retractors. Before and following use of the retractors, muscle biopsies were taken from the multifidus muscle for analysis using birefringence techniques. RESULTS: A significant increase in intramuscular pressure (P < 0.001) was observed during surgery. On removal of retractors, this pressure returned to or near to the original value. Analysis of muscle biopsies using calcium activated adenosine triphosphatase birefringence revealed a reduction in muscle function following prolonged use of self-retaining retractors. CONCLUSIONS: A substantial rise in pressure in the erector spinae muscle during posterior spinal surgery was observed, and this appeared to be associated with marked changes in the function of the muscles. This could be an important factor in the generation of operative scar tissue and postoperative dysfunction of the spinal muscles.

Adult↗
PubMed2003

Biomechanics and electromyography of a common idiopathic low back disorder.

STUDY DESIGN: In vivo feline preparation groups loaded into lumbar flexion at different magnitudes and an unloaded control group. OBJECTIVE: To demonstrate that a static, constant load flexion of the lumbar spine results in a complex neuromuscular disorder. SUMMARY OF BACKGROUND DATA: Epidemiology suggests that static lumbar flexion is a cause of low back disorders. There is little direct experimental evidence describing the physiologic and biomechanical processes that elicit the disorder. Recent evidence shows that static flexion of the spine under constant displacement results in muscular spasms and a prolonged recovery period. The response of the spine to flexion under constant load of various magnitudes (as opposed to constant displacement) is not known. It was hypothesized that static lumbar flexion under constant load may elicit creep in spinal ligaments, discs, etc., causing microdamage and development of a neuromuscular disorder. METHODS: The lumbar spine of the feline was subjected to 20 minutes of constant load static flexion at physiologic load intensities from light to heavy while creep of lumbar viscoelastic tissues and EMG from the multifidus muscles of L3-L4 to L5-L6 were recorded. Recordings were continued over a 7-hour rest period after the static flexion was terminated. RESULTS: Spasms and decreasing reflexive EMG were evident during the loading period, and a transient surge of EMG activity occurred at the beginning of the rest period. A second surge of EMG activity was seen 3-4 hours later. The four components of the neuromuscular disorder were present regardless of the load magnitude. A model was developed to quantify the disorder. CONCLUSION: A four-component neuromuscular disorder was elicited by a 20-minute constant load static flexion even when very light loads were applied. The disorder was elicited by creep of the viscoelastic tissues, which resulted in spasms and muscular hyperexcitability lasting for >24 hours. Although the disorder was transient, the physiologic and biomechanical principles associated with its development could also explain cumulative trauma disorders.

Animals↗
PubMed2004

Static load repetition is a risk factor in the development of lumbar cumulative musculoskeletal disorder.

STUDY DESIGN: In vivo feline model subjected to variable number of repetitions of a short static lumbar flexion followed by an equally long rest period. OBJECTIVES: The purpose of this study was to determine the influence of the number of repetitions as a risk factor in promoting a cumulative low back disorder in the feline model. SUMMARY OF BACKGROUND DATA: Epidemiologic data point out that the increased number of repetitions of static lumbar loading is a major risk factor in the development of cumulative low back disorder. Biomechanical and physiologic confirmation of the epidemiology is lacking. Recent work demonstrated that repetitive static loading results in accumulation of creep in the lumbar viscoelastic tissues, resulting in a neuromuscular disorder consisting of spasms during loading and hyperexcitability of lumbar muscles during following rest. It was also shown that the load magnitude is a major risk factor. It is hypothesized that increased number of repetitions of static load periods result in increased severity of the resulting neuromuscular disorder. METHODS: Static lumbar flexion of 10 minutes duration followed by 10 minutes rest was repeated three times in one experimental group, six times in the second, and nine times in the third group. In all groups, the creep developing in the lumbar viscoelastic tissues as well as the reflexive EMG from the multifidus were monitored during the flexion/rest periods and throughout a 7-hour recovery period after the repetitions. RESULTS: Creep developed and accumulated during each of the flexion/rest periods in the three experimental protocols, with larger residual creep at the end of the nine repetitions. A residual creep was still present at the end of the 7 hours of recovery allowed in each of the three groups. During the flexion/rest sessions, EMG spasms were present, and the presence of an initial hyperexcitability was detected during the 7 hours of recovery in all the preparations. The presence of a delayed hyperexcitability was revealed only in the group subjected to nine flexion/rest periods, while it was not observed in the groups subjected to three and six flexion/rest repetitions. The statistical analysis (post hoc Fisher test) performed on the normalized integrated EMG and displacement data during the recovery phase showed a significant difference between the nine repetitions group and the other two groups (P < 0.0001). The two-way ANOVA analysis revealed a significant effect of time (P < 0.005) and number of repetitions (P < 0.0001) on all considered parameters. CONCLUSIONS: It was concluded that a cumulative neuromuscular disorder develops because of repetition of static lumbar flexion, and the severity of the disorder provoked is magnified by the number of repetitions. Despite the highly favorable 1:1 work-to-rest ratio and the 7-hour post loading rest period, a full recovery of creep was not obtained in this study.

Animals↗
PubMed2006

Evaluation of the flexion relaxation phenomenon of the trunk muscles in sitting.

STUDY DESIGN: A normative, single-group study was conducted. OBJECTIVE: To investigate the flexion relaxation phenomenon in the thoraco-lumbopelvic muscles among a pain-free population when moving from an upright to a slump sitting posture. SUMMARY OF BACKGROUND DATA: The presence of the flexion relaxation phenomenon (FRP) of the back muscles is well documented at end-range spinal flexion when standing. This phenomenon is commonly found disrupted in low back subjects. However, whether FRP occurs in sitting remains controversial. METHODS: The sample consisted of 24 healthy pain-free adults. Surface electromyography was used to measure activity in the superficial lumbar multifidus (SLM), the thoracic erector spinae (TES), and the transverse fibers of the internal oblique (IO) muscles while subjects moved from an erect to a slump sitting posture. An electromagnetic motion-tracking device simultaneously measured thoracolumbar kinematics during this task. RESULTS: There was a significant decrease in both the SLM and the IO activity when moving from an erect to a slump sitting posture (P = 0.001 and P = 0.004, respectively), indicating the presence of FRP. TES activity was highly variable. While 13 subjects exhibited an increase in activity (P = 0.001), 11 demonstrated a decrease in activity (P = 0.001), indicating the presence of FRP. FRP occurred in the mid-range of spinal flexion for the SLM, IO and TES when present. CONCLUSION: The findings show that the SLM and the IO are facilitated in neutral lordotic sitting postures and exhibit FRP at mid range flexion while moving from upright sitting to slump sitting. These findings show that FRP in sitting differs from that in standing. Variable motor patterns (activation or FRP) of the TES were observed. These findings suggest that sustaining mid to end-range flexed sitting spinal postures result in relaxation of the spinal stabilizing muscles.

Adult↗
PubMed2006

Fatty infiltration in the cervical extensor muscles in persistent whiplash-associated disorders: a magnetic resonance imaging analysis.

STUDY DESIGN: Cross-sectional investigation of muscle changes in patients suffering from persistent whiplash-associated disorders (WAD). OBJECTIVES: To quantitatively compare the presence of fatty infiltrate in the cervical extensor musculature in a cohort of chronic whiplash patients (WAD II) and healthy control subjects across muscle and cervical segmental level. SUMMARY OF BACKGROUND DATA: Magnetic resonance imaging (MRI) can be regarded as the gold standard for muscle imaging; however, there is little knowledge about in vivo features of neck extensor muscles in patients suffering from persistent WAD and how fat content alters across the factors of muscle, vertebral segments, age, self-reported pain and disability, compensation status, body mass index, and duration of symptoms. METHODS: A reliable MRI measure for fatty infiltrate was performed of the cervical extensor muscles bilaterally in 113 female subjects (79 WAD, 34 healthy control; 18-45 years, 3 months to 3 years post injury). The measure was performed on all subjects for the rectus capitis posterior minor and major, multifidus, semispinalis cervicis and capitis, splenius capitis, and upper trapezius. RESULTS: The WAD subjects had significantly larger amounts of fatty infiltrate for all of the cervical extensor muscles compared with healthy control subjects (all P < 0.0001). In addition, the amount of fatty infiltrate varied by both cervical level and muscle, with the rectus capitis minor/major and multifidi at C3 having the largest amount of fatty infiltrate (P < 0.0001). Intramuscular fat was independent of age, self-reported pain/disability, compensation status, body mass index, and duration of symptoms. CONCLUSION: There is significantly greater fatty infiltration in the neck extensor muscles, especially in the deeper muscles in the upper cervical spine, in subjects with persistent WAD when compared with healthy controls. Future studies are required to investigate the relationships between muscular alterations and symptoms in patients suffering from persistent WAD.

Adipose Tissue↗
PubMed2006

Comparison of minimally invasive and conventional open posterolateral lumbar fusion using magnetic resonance imaging and retraction pressure studies.

OBJECTIVE: To determine whether minimally invasive lumbar spinal fusion results in less paraspinal muscle damage than conventional open posterior fusion. METHODS: The maximum intramuscular pressure (IMP) generated by a minimally invasive and standard open retractor was compared in cadavers using an ultra-miniature pressure transducer. In a second clinical study, eight patients with either minimally invasive or open posterolateral lumbar spinal fusion underwent magnetic resonance imaging (MRI) scanning approximately 6 months post surgery. MRI was used to estimate edema and atrophy within multifidus, with T2 mapping and diffusion-weighted imaging allowing quantification of differences between the two surgical techniques. RESULTS: IMP measured with the minimally invasive retractor was 1.4 versus 4.7 kPa with the open retractor (P < 0.001). The minimally invasive retractor produced a transient maximal IMP only on initial expansion. Maximum IMP was constant throughout open retractor deployment. Striking visual differences in muscle edema were seen between open and minimally invasive groups on MRI. The mean T2 relaxation time at the level of fusion was 47 milliseconds in the minimally invasive and 90 milliseconds in the open group (P = 0.013). The mean apparent diffusion coefficient was 1357 x 10(-6) mm/s and 1626 x 10(-6) mm(2)/s (P = 0.0184), respectively. CONCLUSIONS: The peak IMP generated by the minimally invasive retractor was significantly less than with the open retractor. Postoperatively, less muscle edema was demonstrated after the minimally invasive lumbar spinal fusion, with lower mean T2 and apparent diffusion coefficient measurements supporting the hypothesis that less damage occurs using a minimally invasive approach.

Adult↗
PubMed1999

On the polymorphism of a sapogenin monohydrate induced by different rotations of water molecules.

The structure of 1beta,3beta,11alpha-trihydroxyspirosta-5,25(27)-diene (C(27)H(40)O(5); a steroidal sapogenin) isolated from Helleborus serbicus Adam 1906 (Ranunculaceae) and crystallized from absolute ethanol as a monohydrate (melting point 519-522 K) had been characterized by two symmetry-independent binary (steroid-water) layers, cross-linked by hydrogen bonds [Kálmán et al. (1985). Acta Cryst. C41, 1645-1647]. Recently, a novel monohydrate was crystallized again from absolute ethanol (source: Helleborus multifidus subspecies serbicus) with a somewhat higher melting point of 525-526 K. X-ray analysis of these crystals [Argay et al. (1998). Acta Chim. Hung. 135, 449-456] revealed a novel polymorph (hereinafter denoted polymorph B), which is also built up by two binary layers of C(27)H(40)O(5) and H(2)O, but in which the relative position of these layers differs from that found in the first modification (polymorph A). Comparing the two polymorphs, layers of one type are found to be similar, displaying identical hydrogen bonding, whereas layers of the second type differ with respect to the orientations adopted by the water molecules; these orientations also differ from those in the layers of the first type. Consequently, by these water rotations, hydrogen bonds, at least partly, are reversed. This leads to two different close packings: in form A four consecutive layers are cross-linked by two homomolecular (hydroxyl.hydroxyl and water.water) hydrogen-bond pairs, while in B there are only heteromolecular hydroxyl.water bonds. These hydrogen-bond dissimilarities together with the differences in the weak CH.X etc. interactions explain the greater stability of the higher melting-point form B.

Journal Article↗
PubMed1993

The axial torque of the lumbar back muscles: torsion strength of the back muscles.

The maximal, axial torque generated by the lumbar back muscles was determined by modelling the action of the 49 fascicles of longissimus thoracis, iliocostalis lumborum and the lumbar multifidus on radiographs of the lumbar spine of nine young male subjects in upright standing and in full lumbar flexion. No single fascicle exerted more than 2 Nm of axial torque in the upright posture, and the collective torque of all muscles acting a segment did not exceed 5 Nm. All torques were considerably less in full flexion. The lumbar back muscles exert very little torque on the lumbar spine, and contribute only about 5% of the total torque involved in trunk rotation. None of the lumbar back muscles can be considered a rotator. The oblique abdominal muscles are the principal rotators of the trunk. Preventative and rehabilitation programmes concerned with torsion injuries should focus on the abdominal muscles rather than the back muscles for stability in axial rotation.

Back↗
PubMed1982

Lumbar back muscle activity in relation to trunk movements during locomotion in man.

The function of lumbar back muscles was studied by relating their activity patterns to trunk movements in 7 healthy adult males during normal walking (1.0-2.5 m/s) and running (2.0-7.0 m/s) on a treadmill. The movements of the trunk in the sagittal and frontal planes were recorded with a Selspot optoelectronic system using infrared light emitting diodes as markers. The electromyographic (EMG) activity from the two main portions of the lumbar erector spinae muscles (Multifidus and Longissimus) was recorded bilaterally with intramuscular wire electrodes. The angular displacements of the trunk showed regular oscillations, but their shape, magnitude and relation to the step cycle were different in the two planes (sagittal and frontal) and varied with speed and mode of progression. The EMG pattern in both muscles showed a bilateral cocontraction with two main bursts of activity per step cycle starting just before each foot was placed on the ground. Relating the EMG to the movements of the trunk indicated that the main function of the lumbar erector spinae muscles is to restrict excessive trunk movements. During walking this restricting action is most evident for movements in the frontal plane, whereas in running the lumbar back muscles mainly control the movements in the sagittal plane.

Adaptation, Physiological↗
PubMed2007

Electromyography of superficial and deep neck muscles during isometric, voluntary, and reflex contractions.

Increasingly complex models of the neck neuromusculature need detailed muscle and kinematic data for proper validation. The goal of this study was to measure the electromyographic activity of superficial and deep neck muscles during tasks involving isometric, voluntary, and reflexively evoked contractions of the neck muscles. Three male subjects (28-41 years) had electromyographic (EMG) fine wires inserted into the left sternocleidomastoid, levator scapulae, trapezius, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles. Surface electrodes were placed over the left sternohyoid muscle. Subjects then performed: (i) maximal voluntary contractions (MVCs) in the eight directions (45 deg intervals) from the neutral posture; (ii) 50 N isometric contractions with a slow sweep of the force direction through 720 deg; (iii) voluntary oscillatory head movements in flexion and extension; and (iv) initially relaxed reflex muscle activations to a forward acceleration while seated on a sled. Isometric contractions were performed against an overhead load cell and movement dynamics were measured using six-axis accelerometry on the head and torso. In all three subjects, the two anterior neck muscles had similar preferred activation directions and acted synergistically in both dynamic tasks. With the exception of splenius capitis, the posterior and posterolateral neck muscles also showed consistent activation directions and acted synergistically during the voluntary motions, but not during the sled perturbations. These findings suggest that the common numerical-modeling assumption that all anterior muscles act synergistically as flexors is reasonable, but that the related assumption that all posterior muscles act synergistically as extensors is not. Despite the small number of subjects, the data presented here can be used to inform and validate a neck model at three levels of increasing neuromuscular-kinematic complexity: muscles generating forces with no movement, muscles generating forces and causing movement, and muscles generating forces in response to induced movement. These increasingly complex data sets will allow researchers to incrementally tune their neck models' muscle geometry, physiology, and feedforward/feedback neuromechanics.

Adult↗
PubMed1997

Resistance training and human cervical muscle recruitment plasticity.

This study examined cervical neuromuscular adaptations to resistance training. The ResX group performed conventional resistance training plus head-extension exercise. Another group performed only conventional resistance training, and the control group performed no resistance exercise. Muscle use during head extension was determined by quantifying shifts in T2 in serial-transaxial magnetic resonance images of the neck. ResX was the only group that showed a training effect. Training decreased (P < 0.05) the cross-sectional area (CSA) of cervical muscle used to perform submaximal head extension by 31%. This reflected a decrease (P < 0.05) in relative use of the splenius capitis, semispinalis capitis, and semispinalis cervicis and multifidus muscles by about one-third; their percentage of CSA showing contrast shift was reduced from 60 to 40% on average. This same exercise evoked no contrast shift in the levator scapulae, longissimus capitis and cervicis, and scalenus medius and anterior muscles posttraining, yet 20% or more of their CSA was engaged pretraining. The relative CSA of cervical musculature that was used to perform maximal head extension was increased (P < 0.05) 16% by training. The findings suggest functional redundancy of neck musculature that can be modified by training; submaximal tasks can be performed despite cessation of recruitment of individual muscles, yet recruitment can be increased for maximal efforts. These results also suggest that neuromuscular adaptations to training require a specific cervical exercise.

Adaptation, Physiological↗