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PubMed1995

The influence of trunk muscle coactivity on dynamic spinal loads.

STUDY DESIGN: Measured trunk muscle activity was employed in a biomechanical model to determine the influence of including or neglecting muscle coactivity on predicted spinal loads. OBJECTIVES: The purpose of this investigation was to examine the influence of muscle coactivity on spinal load. SUMMARY OF BACKGROUND DATA: Electromyographic patterns in the trunk musculature have demonstrated significant levels of cocontraction during lifting exertions. Biomechanical analyses of musculoskeletal loading are often mathematically constrained from including muscle coactivity. Models that attempt to include coactive behavior are complex and difficult to implement. METHODS: Electromyographic data were collected from five trunk muscle pairs while subjects performed dynamic lifting exertions. A validated, electromyographically assisted biomechanical model was used to compute relative muscle force, lifting moment, and spinal load. Results were generated and compared from analyses that included from one to five simultaneously active muscle pairs. RESULTS: Trunk extensor muscles generate lifting moments as much as 47% greater than the applied lifting moment to offset flexor antagonism. Analyses that neglect muscle coactivity during dynamic lifting exertions may underestimate spinal compression by as much as 45% and shear forces by as much as 70%. CONCLUSIONS: The level of coactive spinal loading is significantly influenced by the weight of the lifted load as well as trunk extension velocity. Muscle coactivity significantly influences the modeled load in the lumbar spine during lifting exertions and should be considered if an accurate measure of spinal loading of desired.

Biomechanical Phenomena↗

PubMed1995

Isometric and dynamic performances of the trunk and associated factors.

STUDY DESIGN: Static and dynamic performances of the trunk were measured on an isoinertial device and data were collected regarding the working conditions and the anthropometric and psychosocial characteristics of the workers. OBJECTIVES: To describe the difference in static and dynamic performances of the trunk between workers with and without low back pain and to investigate the anthropometric, personal, and occupational factors associated with these performances. SUMMARY OF BACKGROUND DATA: The isometric torque and the parameters of displacement, velocity, and torque during dynamic tests were chosen to describe the isoinertial performances of the trunk. Dynamic characteristics in particular were investigated because it has been suggested in the literature that these discriminate best between workers with and without low back pain. METHODS: The protocol included a 52-item questionnaire, a clinical examination with a series of anthropometric measurements, and the isometric and dynamic tests (against 25% and 50% of the isometric values) on the isostation. RESULTS: The variables significantly associated with the trunk performances were weight, height, muscularity, sports, and leisure activities as positive factors, and linearity, health problems, and vehicle driving as negative factors. When these covariates were taken into consideration, the significant differences between subjects with and without low back pain were related only to the velocities during dynamic tests, which were reduced by 5.9%. CONCLUSIONS: The performances of the trunk are associated mainly with the anthropometric characteristics of the subjects but also with factors such as lumbar status, health, working conditions, and leisure activities.

Adult↗

PubMed1997

Stabilizing function of trunk flexor-extensor muscles around a neutral spine posture.

STUDY DESIGN: This study examined the coactivation of trunk flexor and extensor muscles in healthy individuals. The experimental electromyographic data and the theoretical calculations were analyzed in the context of mechanical stability of the lumbar spine. OBJECTIVES: To test a set of hypotheses pertaining to healthy individuals: 1) that the trunk flexor-extensor muscle coactivation is present around a neutral spine posture, 2) that the coactivation is increased when the subject carries a load; and 3) that the coactivation provides the needed mechanical stability to the lumbar spine. SUMMARY OF BACKGROUND DATA: Theoretically, antagonistic trunk muscle coactivation is necessary to provide mechanical stability to the human lumbar spine around its neutral posture. No experimental evidence exists, however, to support this hypothesis. METHODS: Ten individuals executed slow trunk flexion-extension tasks, while six muscles on the right side were monitored with surface electromyography: external oblique, internal oblique, rectus abdominis, multifidus, lumbar erector spinae, and thoracic erector spinae. Simple, but realistic, calculations of spine stability also were performed and compared with experimental results. RESULTS: Average antagonistic flexor-extensor muscle coactivation levels around the neutral spine posture as detected with electromyography were 1.7 +/- 0.8% of maximum voluntary contraction for no external load trials and 2.9 +/- 1.4% of maximum voluntary contraction for the trials with added 32-kg mass to the torso. The inverted pendulum model based on static moment equilibrium criteria predicted no antagonistic coactivation. The same model based on the mechanical stability criteria predicted 1.0% of maximum voluntary contraction coactivation of flexors and extensors with zero load and 3.1% of maximum voluntary contraction with a 32-kg mass. The stability model also was run with zero passive spine stiffness to simulate an injury. Under such conditions, the model predicted 3.4% and 5.5% of maximum voluntary contraction of antagonistic muscle coactivation for no extra load and the added 32 kg, respectively. CONCLUSIONS: This study demonstrated that antagonistic trunk flexor-extensor muscle coactivation was present around the neutral spine posture in healthy individuals. This coactivation increased with added mass to the torso. Using a biomechanical model, the coactivation was explained entirely on the basis of the need for the neuromuscular system to provide the mechanical stability to the lumbar spine.

Adult↗

PubMed2003

Comparison of motion restriction and trunk stiffness provided by three thoracolumbosacral orthoses (TLSOs).

The amounts of thoracic and lumbar spine motion restriction and passive trunk stiffness provided by three thoracolumbosacral orthoses (TLSOs) (Aspen TLSO, Boston Body Jacket, and CAMP TLSO) were compared. Ten subjects executed maximum trunk flexion, extension, and lateral bending motions. The spine motion was measured noninvasively with a thin strain gauge device (Flexducer), and passive trunk stiffness around the neutral posture was estimated from an electromyography-assisted biomechanical model. No significant differences in either the restriction of motion or the amount of added passive trunk stiffness were found between the three orthoses. The subjects also did not perceive any difference in the restriction of motion but rated the Aspen TLSO significantly more comfortable than the other two orthoses. The rigid custom orthosis design may not be important for restricting the spine motion and providing passive trunk stiffness, or there may be other measures that reflect better the function of orthoses.

Adult↗

PubMed2003

Effects of unexpected lateral mass placement on trunk loading in lifting.

STUDY DESIGN: A repeated measurements experiment of spinal loading in healthy subjects. OBJECTIVES: To test whether unexpected lateral mass placement increases low back loading and trunk movement when subjects are lifting a mass in upright posture. SUMMARY OF BACKGROUND DATA: Epidemiologic studies suggest that sudden, unexpected loading will lead to low back pain. Also, asymmetric loading is considered to be harmful to the spine. It can be anticipated that unexpected asymmetric loading will increase the risk of injury even more. METHODS: Ten subjects lifted in an upright posture a crate, in which a mass of 10 kg was placed laterally at the left side either expectedly or unexpectedly. The crate reaction forces, body movements, and trunk muscle activity were measured. From these, the L5-S1 net moments and muscle forces were estimated. RESULTS: Unexpected lateral placement of the mass caused no clear increase in peak low back loading. The stiffness of the trunk was lower in the unexpected condition, which, in combination with inadequate net moments produced, resulted in movement of the trunk to the side of the displaced mass. CONCLUSIONS: Unexpected lateral mass placement does not increase the compression force. Perturbed trunk movement and lower muscle forces indicated a decreased stability of the spine, which may imply an injury risk.

Adult↗

PubMed2003

Comparison between tests of fatigue and force for trunk flexion.

STUDY DESIGN: A quasi-experimental study was conducted. OBJECTIVE: To compare intraindividual differences between trunk flexion isometric force, fatigue during isometric contraction (isometric fatigue), and fatigue during sit-ups (dynamic fatigue). SUMMARY OF BACKGROUND DATA: Trunk flexion force and trunk flexion fatigue commonly are used to assess trunk flexion fitness. The use of one test is appropriate only if the tests are highly correlated. METHODS: This study measured force and either isometric fatigue (time to task failure, n = 79) or dynamic fatigue (number of sit-ups in 2 minutes, n = 73) in self-selected, healthy secondary school (I-III) subjects. In 15 subjects, both isometric and dynamic fatigue were measured. RESULTS: After control was used for upper body mass, the R2(adj) was 0.34 between isometric force and isometric fatigue, 0.31 between isometric force and dynamic fatigue was, and 0.27 between dynamic fatigue and isometric fatigue. Including gender in the model did not affect the results. CONCLUSIONS: The lack of a high correlation between trunk flexion isometric fatigue, dynamic fatigue, and isometric force suggests that health care professionals should be careful to select the test that answers their particular needs or question.

Abdomen↗

PubMed2006

Mechanical load of the lumbar spine during forward bending motion of the trunk-a biomechanical study.

STUDY DESIGN: We investigated the mechanical load of the lumbar spine caused by changes of posture and carried load. OBJECTIVE: To clarify the relationship between the actual and theoretical load of the lumbar spine with and without application of external weights. SUMMARY OF BACKGROUND DATA: There is sparse knowledge regarding the relationship between the intradiscal pressure and trunk muscle activities during forward bending motion. METHODS: The measurements of intradiscal pressure, electromyogram activities of the trunk muscles, and motion analysis of the trunk in 3 young healthy men were performed simultaneously with and without lifting a weight of 10 kg. The recorded values were compared with theoretical values based on the principle of levers. RESULTS: The load of the lumbar spine and electromyogram activities of the back muscles increased in proportion to the tilting angle with and without external weights. However, the external weights induced no significant activity in the abdominal muscles. The actual measurement values were larger than the theoretical values at all tilting angles of the trunk. CONCLUSIONS: We found that the increase of the actual spinal load during trunk flexion in healthy individuals consisted of the theoretical spinal load and load generated by the back muscle activities.

Adult↗

PubMed2006

Effects of abdominal muscle coactivation on the externally preloaded trunk: variations in motor control and its effect on spine stability.

STUDY DESIGN: A repeated measures biomechanical analysis of the effects of abdominal bracing in preparation for a quick release of the loaded trunk. OBJECTIVES: To quantify the ability of individuals to abdominally brace the externally loaded trunk, and assess their success in achieving and enhancing appropriate spine stability. SUMMARY OF BACKGROUND DATA: Spine stability requires trunk muscle coactivation, which demands motor control skill that differs across people and situations. The quick release protocol may offer insight into the motor control scheme and subsequent effect on spine stability. METHODS: There were 10 individuals who sat, torso upright, in an apparatus designed to foster a neutral spine position. They were instructed to support a posteriorly directed load to the trunk in either their naturally chosen manner, or by activating the abdominal muscles to 10%, 20%, or 30% of maximum ability. The externally applied load was then quickly released, thereby unloading the participant. Muscle pre-activation patterns, spine stability, and kinematic measures of trunk stiffness were quantified. RESULTS: Participants were able to stabilize their spine effectively by supporting the load in a naturally selected manner. Conscious, voluntary overdriving of this natural pattern often resulted in unbalanced muscular activation schemes and corresponding decreases in stability levels. CONCLUSIONS: Individuals in an externally loaded state appear to select a natural muscular activation pattern appropriate to maintain spine stability sufficiently. Conscious adjustments in individual muscles around this natural level may actually decrease the stability margin of safety.

Abdominal Muscles↗

PubMed2005

The relation of joint laxity and trunk rotation.

A study was designed to evaluate the joint laxity during scoliosis screening, and to show if there is a relation of joint laxity values to the trunk rotation. One thousand, two hundred and seventy-three children (598 females, 675 males) with an average age of 10.4 years were screened with a scoliometer and forward bending for trunk rotations. Scapular and shoulder elevations, flexible pes planus were recorded and joint laxity was evaluated with the Beighton score. There was high inter-observer and intra-observer reliability for both scoliometer and Beighton scores. In 41 children (3.2%) with Beighton score 7 or higher, trunk rotation measurements were higher than for the rest of the children. Trunk rotation measurements of 7 degrees or higher were found in 30 children, who were more lax than the rest of the group and were invited for radiography, with a detection of curves between 11 and 18 degrees in 10 of them. The Beighton score is a practical and reliable method for defining joint laxity. Although the number of patients with scoliosis was limited, there are findings supporting the relation between joint laxity and scoliosis. Moreover, there was increased laxity in children with increased trunk rotations. Ligamentous laxity may be one of the causes changing the contour of the back.

Adolescent↗

PubMed1990

A nerve cuff technique for selective excitation of peripheral nerve trunk regions.

Numerical modeling and experimental testing of a nerve cuff technique for selective stimulation of superficial peripheral nerve trunk regions is presented. Two basic electrode configurations ("snug" cuff monopolar and tripolar longitudinally aligned dots) have been considered. In addition, the feasibility of "steering" excitation into superficial nerve trunk regions using subthreshold levels of current flow from an electrode dot located on the opposite side of the nerve has been tested. Modeling objectives were to solve for the electric field that would be generated within a representative nerve trunk by each electrode configuration; and to use a simple nerve cable model to predict the effectiveness of each configuration in producing localized excitation. In three acute experiments on cat sciatic nerve the objective was to characterize the effectiveness of each electrode configuration in selectively activating only the medial gastrocnemius muscle. Modeling and experimentation both suggest that longitudinally aligned tripolar dot electrodes on the surface of a nerve trunk, and bounded by a layer of insulation (such as a nerve cuff), will restrict excitation to superficial nerve trunk regions more successfully than will monopolar dot electrodes. Excitation "steering" will improve the spatial selectivity of both monopolar and tripolar electrode configurations.

Animals↗

PubMed1995

Healthy young and old women differ in their trunk elevation and hip pivot motions when rising from supine to sitting.

OBJECTIVE: To describe the differences between healthy young and older women in regards to trunk elevation and hip pivot motions when rising from a supine to a seated position. DESIGN: Cross-sectional comparison. SETTING: University laboratory. PARTICIPANTS: Two groups of healthy female volunteers: young adult female controls (n = 22, mean age 23.5 years) and community-dwelling older female adults (n = 17, mean age 73.8 years). MEASUREMENTS: Subjects were videotaped as they performed three controlled bed mobility tasks, starting from a supine position: (1) rising to a seated position at the edge of a firm plinth surface (SS); and rising to a seated position without moving to the edge of the bed while either (2) using hands (SUH) or (3) not using hands (SUNH). A series of movements involving the trunk were identified as subjects performed the SS task. RESULTS: The older women were more likely to rotate and laterally flex their trunks, particularly in the later phases of the SS task. In addition, during the SS task, the older group was more likely to bear weight on their hip/gluteal area, particularly in the later phases, and more likely to use a broad pivot base, consisting of the hip and the elbow. While all young and old performed the SUH task, less than half of the older group could complete the SUNH task. Moreover, the subgroup of older adults who could not complete the SUNH task may have accounted for much of the differences between the young and the old on the SS task. CONCLUSION: Healthy young and older women differ in their ability to rise from a supine to sitting position, primarily in the strategies used to elevate the trunk and facilitate a pivot. Trunk flexion ability likely contributes to the age group differences noted in rising. These data provide the basis for a biomechanical analysis of the critical body segment motions and the strengths required to perform bed mobility tasks.

Adult↗

PubMed2004

Group treatment improves trunk strength and psychological status in older women with vertebral fractures: results of a randomized, clinical trial.

OBJECTIVES: To assess whether group exercise and coping classes reduce physical and psychological impairments and functional disability in older women with prevalent vertebral fractures (VFs). DESIGN: Randomized, controlled trial (modified cross-over) with site as unit of assignment; testing at baseline and 3, 6, 9, and 12 months. SETTING: Nine North Carolina retirement communities. PARTICIPANTS: One hundred eighty-five postmenopausal Caucasian women (mean age 81), each with at least one VFs. INTERVENTION: The intervention group had 6 months of exercise (3 meetings weekly, 45 minutes each) and coping classes (2 meetings weekly, 45 minutes each) in Phase 1, followed by 6 months of self-maintenance. The control group had 6 months of health education control intervention (1 meeting weekly, 45 minutes) in Phase 1, followed by the intervention described above. MEASUREMENTS: Change in trunk extension strength, change in pain with activities, and change in psychological symptoms. RESULTS: Between-group differences in the change in trunk extension strength (10.68 foot pounds, P<.001) and psychological symptoms (-0.08, P=.011) were significant for Phase 1. Changes in pain with activities did not differ between groups (-0.03, P=.64); there was no change in the pain endpoint. In Phase 2, controls showed significant changes in trunk strength (15.02 foot pounds, P<.001) and psychological symptoms (-0.11, P=.006) from baseline. Change in pain with activities was not significant (-0.03, P=.70). During self-maintenance, the intervention group did not worsen in psychological symptoms, but improved trunk extension strength was not maintained. CONCLUSION: Weak trunk extension strength and psychological symptoms associated with VFs can be improved in older women using group treatment, and psychological improvements are retained for at least 6 months.

Activities of Daily Living↗

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↗

PubMed1985

Motor control of voluntary trunk movements in standing.

The pattern of activity in different trunk muscles during voluntary trunk movements was studied in the standing position in man. The electromyographic activity from ventral and dorsal trunk muscles on the left and right sides were recorded together with the movements in the sagittal and frontal planes (Selspot optoelectronic system). Movement direction, amplitude, velocity and initial posture were varied. In all movements there was a basic pattern of alternation between antagonist muscle groups. Fast movements were initiated by a sharp burst of activity, whereas slow flexions and side bendings resulted from a decrease in antigravity muscle activity. Movement amplitude was related to the magnitude of the initiating burst, and also to the time of onset of antagonist muscle activity with a braking effect. The contribution of passive internal forces in the braking of a movement was indicated by the myoelectrical pattern of activity, particularly in slow large side bendings, where ipsilateral activity was present at the end of the movement. Sagittal movements starting at different initial trunk inclinations resulted in shifts in onset time and duration between antagonist muscles. The observed modifications are specific adaptations of the motor program to balance changes in mechanical conditions, such as angular acceleration, moment arm for the gravitational force, and intrinsic forces of active and passive structures surrounding the spine and pelvis. In conclusion, the present results demonstrate that trunk movements are generated and controlled by specific patterns of muscle coordination.

Adult↗

PubMed1987

Chronic block of the cervical trunk increases synaptic efficacy in the superior and stellate ganglia of the guinea-pig.

1. The effects of chronic conduction block with tetrodotoxin (TTX) of the cervical sympathetic trunk on synapses in the superior and stellate ganglia were examined in vitro with intracellular recording techniques. 2. The mean maximum amplitude of excitatory post-synaptic potentials (e.p.s.p.s) evoked in superior cervical ganglion neurones by stimulation of the cervical sympathetic trunk was increased significantly after 2 or 4 days of block. The electrical properties of the ganglion cells were not appreciably changed by the period of inactivity. 3. Chronic conduction block for 4 days also resulted in a significant increase in the amplitude of the e.p.s.p.s. evoked in stellate ganglion cells by active collaterals of the blocked fibres. 4. The number of steps in the synaptic response elicited in individual stellate ganglion neurones by graded stimulation of the ansa subclavia and the subclavian trunk (which join to form the cervical sympathetic trunk) was increased after 4 days of conduction block. 5. These results show that elimination of impulse activity in the cervical sympathetic trunk increased synaptic efficacy at the disused synapses in the superior cervical ganglion and at the active synapses in the stellate ganglion. In the latter case, collaterals of the blocked fibres apparently formed new synaptic connexions on stellate ganglion cells.

Animals↗

PubMed1991

A continuum model of elephant trunks.

A continuum model is presented that relates the trunk parameters of loading, geometry, and muscle structure to the necessary conditions of static equilibrium. Linear theory for stress-strain behavior is used to describe an elephant trunk for an incremental displacement as the animal slowly lifts a weight at the trunk tip. With this analysis and experimental values for the trunk parameters, the apparent trunk stiffness Ea is estimated for the living animal. For an Asian elephant with a maximum compression strain of 33 percent, Ea is of the order of 10(6) N/m2. The continuum model is quite general and may be applied to similar nonskeletal appendages and bodies of other animals.

Animals↗

PubMed2006

Influence of shoulder abduction and lateral trunk tilt on peak elbow varus torque for college baseball pitchers during simulated pitching.

Elbow varus torque is a primary factor in the risk of elbow injury during pitching. To examine the effects of shoulder abduction and lateral trunk tilt angles on elbow varus torque, we conducted simulation and regression analyses on 33 college baseball pitchers. Motion data were used for computer simulations in which two angles-shoulder abduction and lateral trunk tilt-were systematically altered. Forty-two simulated motions were generated for each pitcher, and the peak elbow varus torque for each simulated motion was calculated. A two-way analysis of variance was performed to analyze the effects of shoulder abduction and trunk tilt on elbow varus torque. Regression analyses of a simple regression model, second-order regression model, and multiple regression model were also performed. Although regression analyses did not show any significant relationship, computer simulation indicated that the peak elbow varus torque was affected by both angles, and the interaction of those angles was also significant. As trunk tilt to the contralateral side increased, the shoulder abduction angle producing the minimum peak elbow varus torque decreased. It is suggested that shoulder abduction and lateral trunk tilt may be only two of several determinants of peak elbow varus torque.

Abdomen↗

PubMed1999

Activation of selected trunk muscles during symmetric functional activities in poststroke hemiparetic and hemiplegic patients.

OBJECTIVE: To compare the EMG activity between the recti abdominii muscles and between the lumbar erector spinae muscles in hemiparetic and hemiplegic patients during functional symmetric trunk movements and to compare patients' EMG activity profiles with those of healthy controls. METHODS: EMG activity from the selected muscles was recorded during three symmetric and time controlled trunk exercises. Data analysis was based on values of cross correlations and of ratios between EMG activity of the bilateral corresponding muscles. RESULTS: In all groups, the highest cross correlations were obtained for both muscles when the muscles acted as prime movers. For the recti abdominii muscles, these values in the patients were comparable with those of the healthy subjects, whereas for the extensor muscles, the highest synchronous activity was displayed in healthy subjects and the lowest in hemiplegic patients. Laterality differences in the amount of EMG activity of the recti abdominii muscles were not biased towards one side. For the extensor muscles, in the controls, the activation levels were higher in the left erector spinae muscle than in the right one in two of the three exercises. Similarly, in the extensor muscles of the hemiparetic patients, activity on the paretic side was higher than on the non-paretic side in two exercises. CONCLUSIONS: In patients with a supratentorial poststroke hemiparesis or hemiplegia, bilateral corresponding axial trunk muscles co-contract during symmetric trunk activities. Synchronous activation is at its highest level during voluntary dynamic tasks and is greater in the recti abdominii than in the erector spinae muscles. For both muscles, EMG activation levels on the paretic side were not lower than on the non-paretic side. Thus, the assertion that the muscles on the paretic side are activated to a lesser extent than their counterparts on the non-paretic side during symmetric trunk movements was not confirmed.

Aged↗