Changes in the flexion-relaxation response induced by hip extensor and erector spinae muscle fatigue

Background  

The flexion-relaxation phenomenon (FRP) is defined by reduced lumbar erector spinae (ES) muscle myoelectric activity during full trunk flexion. The objectives of this study were to quantify the effect of hip and back extensor muscle fatigue on FRP parameters and lumbopelvic kinematics.     

An Unstable Base Alters Limb and Abdominal Activation Strategies During the Flexionrelaxation Response

The flexion-relaxation phenomenon consisting of an erector spinae silent period occurring with trunk flexion can place considerable stress upon tissues. Since individuals often flex their trunks while unstable, the purpose of the study was to examine the effect of an unstable base on the flexion-relaxation response. Fourteen participants flexed at the hips and back while standing on a stable floor or an unstable dyna-disc. Hip and trunk flexion were repeated four times each with one-minute rest. Electromyographic (EMG) electrodes were placed over the right lumbo-sacral erector spinae (LSES), upper lumbar erector spinae (ULES), lower abdominals (LA), biceps femoris and soleus. In addition to the flexion-relaxation phenomenon of the ES, a quiescence of biceps femoris and a burst of LA EMG activity was observed with the majority of stable trials. There was no effect of instability on the flexion-relaxation phenomenon of the ULES or LSES. The incidence of a biceps femoris silent period while stable was diminished with an unstable base. Similarly, the incidence of a LA EMG burst was curtailed with instability. Soleus EMG activity increased 29.5% with an unstable platform. An unstable base did not significantly affect LSES and ULES EMG flexion-relaxation, but did result in more persistent lower limb and LA activity.

Key Points

• An unstable base did not affect the flexion relaxation response of the erector spinae.
• An unstable base decreased the incidence of biceps femoris quiescent period.
• An unstable base diminished the incidence of the lower abdominals EMG burst.

Key words: Electromyography, erector spinae, hamstrings, trunk flexion     

Intramuscular myoelectric activity and selective coactivation of trunk muscles during lateral flexion with and without load.

STUDY DESIGN: Myoelectric activity of trunk muscles was measured intramuscularly in six healthy subjects as they maintained static trunk postures at 0 degrees, 15 degrees, and 30 degrees of lateral bending, unloaded or holding a 20-kg load in one hand alongside the body. OBJECTIVE: To determine the position and load dependency of the agonistic and antagonistic myoelectric responses of deep and superficial trunk lateral flexor muscles. SUMMARY OF BACKGROUND DATA: Loading of the trunk in lateral bending is associated with incidences of low back pain. The neuromotor control of muscles surrounding the spine may be decisive for its vulnerability. Earlier documentation of the activation pattern of trunk muscles, particularly those situated deeply, is incomplete. METHODS: Trunk angle was measured between S1-C7 and the vertical with a protractor. Electromyographic activity was recorded unilaterally from eight trunk muscles using intramuscular fine-wire electrodes inserted under the guidance of ultrasound. RESULTS: The electromyographic data showed that all muscles on the side contralateral to the load, except rectus abdominis, had their highest activity while loaded in the position most laterally flexed to the loaded side. The degree of bilateral coactivation was greater for the ventral than for the dorsal muscles. CONCLUSIONS: The myoelectric responses of most lumbar trunk muscles to static lateral flexion were dependent on trunk position and loading. The abdominal muscles demonstrated more coactivation than the other trunk muscles, and thus appeared to contribute more to trunk stabilization in laterally bent and loaded trunk positions.     

Loads on the lumbar trunk during level walking

The goal of this study was to estimate the loads internal to the lumbar trunk that arise during level walking. To do this, (a) trunk muscle activities were calibrated in terms of muscle contraction force levels in a set of isometric exertions; (b) trunk muscle myoelectric activities were measured during level walking; and then (c) the muscle contraction forces that arose during walking were calculated from these measurements and calibrations. Lumbar trunk muscle myoelectric activities were quantified in 10 healthy young males. Myoelectric activities were monitored using eight bipolar surface electrode pairs placed around the trunk at the level of the third lumbar vertebrae. The subjects first performed four static weight-resisting tasks to calibrate muscle force/activity relationships. They then traversed a 8.25 m walkway three times each at cadences of 72 and 120 steps/min. A biomechanical model incorporating 22 lumbar trunk muscles was used to predict muscle contraction forces for the calibration tasks. Predicted forces were linearly correlated with the measured myoelectric activities for these tasks. The regression equations were then interpolated to estimate the muscle contraction forces from the myoelectric data during gait. Peak contraction forces for the iliocostalis muscles were calculated to be approximately 55 N per side, corresponding to total erector spinae peak contractions on the order of 140 N per side. For the other six muscles that were monitored, contraction forces were less than 15 N per side. This suggests that peak net reaction moments and peak spine compressions on the lumbar trunk during these walking tasks were on the order of 15 Nm and 1.2 times body weight, respectively.     

Intradiskal pressure, intra-abdominal pressure and myoelectric back muscle activity related to posture and loading

Intradiskal pressures, intra-abdominal pressures and myoelectric activities of posterior back muscles have been measured simultaneously in vivo in 4 subjects. Five different angles of forward flexion were studied while externally loading the trunk with 200N. At 30 degrees of forward flexion studies were made when the load was increased from 0 to 300N. Asymmetric loading was studied with the trunk erect, in lateral flexion and in rotation. The measurement parameter values all increased when the angle of flexion increased and when the external load was increased at a fixed angle of flexion. Linear relationships were established. During asymmetric loading pressure values and the myoelectric activity increased. The increase in myoelectric activity was comparatively greater on the contralateral side of the lumbar region and on the ipsilateral side of the thoracic region. The disk pressure, the intra-abdominal pressure, and the FRA-values were higher throughout when the trunk was loaded in rotation, than in lateral flexion.     

躯干侧屈时腰背肌、腹肌的肌电活动及其稳定脊柱的生理功能

目的 研究躯干侧屈时，负重或非负重情况下腰背肌、腹肌的肌电活动和稳定脊柱的生理功能。方法 应用B型超声波导入肌内线性电极，测量5位正常男性和1位正常女性在C7-S1侧屈、负重和非负重情况下的八块同侧和对侧腰背肌、腹肌的肌电信号，标准处理和量化肌电信号，计算双侧肌的协同活动率。结果 除腹直肌外，对侧肌的肌电强度随着侧屈角度和负重的增加而增加；同侧肌肌电活动较低，仅腹部肌肉与躯干位置、负重有协同增加的趋势。同侧和对侧腹肌的协同活动率大于腰背肌。腹横肌的活动与传统认识不同。 结论 大多数腰肌的肌电反应取决于躯干侧屈的位置和是否负重。腹肌较其它躯干肌有更多的协同活动，提示在侧屈和单侧负重时，肌对脊柱稳定性起较大作用。     

Timing of activation of the erector spinae and hamstrings during a trunk flexion and extension task

STUDY DESIGN: Timing of activation of the hamstrings and erector spinae was assessed using surface electromyography. OBJECTIVES: To investigate the influence of posture and movement speed during trunk flexion-extension on the flexion-relaxation response and trunk muscle activation patterns. SUMMARY OF BACKGROUND DATA: The literature contains numerous reports on coactivity and synergistic behavior of major muscle groups during trunk flexion-extension. There are few reports on the timing of muscle activation. METHODS: Six subjects were recruited for a training session and six biweekly test sessions. Ten surface electromyogram electrodes and a lordosimeter were used to record timing of lumbar motion and muscle recruitment in the hamstrings and at four sites in the thoracolumbar region. A 3 x 2 within-subject factorial design was used to test the effects of posture and speed on activation patterns. RESULTS: Patterns of muscle activation were found to be dependent on posture and the direction of movement. The flexion-relaxation response was pervasive in the lumbar region but was less consistent at the T9 and hamstring sites. Significant differences in the delay between electromyogram activation and lumbar motion were found for the standing postures at initiation of extension, in which activation progressed in the caudad-to-cephalad direction. CONCLUSIONS: The flexion-relaxation response is ubiquitous in the lumbar erector spinae and is present in the hamstrings and lower thoracic erector spinae, although not consistently in all subjects. In standing, timing of activation differed significantly by site in extension but not in flexion. Muscle activation patterns and flexion-relaxation were consistent over six biweekly test sessions.     

Effects of noxious stimulation and pain expectations on neuromuscular control of the spine in patients with chronic low back pain

Background context

Alterations of the neuromuscular control of the lumbar spine have been reported in patients with chronic low back pain (LBP). During trunk flexion and extension tasks, the reduced myoelectric activity of the low back extensor musculature observed during full trunk flexion is typically absent in patients with chronic LBP.

Purpose

To determine whether pain expectations could modulate neuromuscular responses to experimental LBP to a higher extent in patients with chronic LBP compared with controls.

Study design

A cross-sectional, case-control study.

Patient sample

Twenty-two patients with nonspecific chronic LBP and 22 age- and sex-matched control participants.

Methods

Trunk flexion-extension tasks were performed under three experimental conditions: innocuous heat, noxious stimulation with low pain expectation, and noxious stimulation with high pain expectation. Noxious stimulations were delivered using a contact heat thermode applied on the skin of the lumbar region (L4–L5), whereas low or high pain expectations were induced by verbal and visual instructions.

Outcome measures

Surface electromyography of erector spinae at L2–L3 and L4–L5, as well as lumbopelvic kinematic variables were collected during the tasks. Pain was evaluated using a numerical rating scale. Pain catastrophizing, disability, anxiety, and fear-avoidance beliefs were measured using validated questionnaires.

Results

Two-way mixed analysis of variance revealed that pain was significantly different among the three experimental conditions (F2,84=317.5; p<.001). Increased myoelectric activity of the low back extensor musculature during full trunk flexion was observed in the high compared with low pain expectations condition at the L2–L3 level (F2,84=9.5; p<.001) and at the L4–L5 level (F2,84=3.7; p=.030). At the L4–L5 level, this effect was significantly more pronounced for the control participants compared with patients with chronic LBP (F2,84=3.4; p=.045). Pearson correlation analysis revealed that increased lumbar muscle activity in full flexion induced by expectations was associated with higher pain catastrophizing in patients with chronic LBP (r=0.54; p=.012).

Conclusions

Repeated exposure to pain appears to generate rigid and less variable patterns of muscle activation in patients with chronic LBP, which attenuate their response to pain expectations. Patients with high levels of pain catastrophizing show higher myoelectric activity of lumbar muscles in full flexion and exhibit greater neuromechanical changes when expecting strong pain.     

The influence of lordosis on axial trunk torque and trunk muscle myoelectric activity.

Force contributions from the facet complex and posterior ligaments during the generation of axial torque are a function of lordosis, and it has been speculated that these forces together with muscular contributions play a role in axial trunk twisting. This study investigated the electromyographic activity of the trunk musculature and torque-generating capacity of the lumbar spine under the conditions of normal lordosis, hyperlordosis, and hypolordosis. Eleven male subjects volunteered for this study. The subjects performed isometric twisting efforts and maximum dynamic twisting efforts at 30 degrees/sec. The myoelectric activity levels (normalized to maximal amplitude obtained from nontwist activities) were quite low despite maximal efforts to generate axial torque (for example: approximately 60% maximum voluntary contraction for latissimus dorsi and even lower for the abdominals). Furthermore, changes in lordosis did not produce any consistent changes in muscle activity, although a hyperlordotic spine produced significantly smaller axial torques, and a hypolordotic spine smaller still. Larger torques were measured during all three conditions of lordosis, as the subjects rotated toward an untwisted position, and lower torques as the subjects rotated away. The opposite trend was observed, however, in myoelectric activity of the agonistic side of latissimus dorsi, the thoracic level of erector spine, and the lumbar level of erector spinae, i.e., larger amplitudes were observed as the trunk was twisted away from the untwisted position. These data suggest that tissues other than muscle (i.e., passive tissue) contribute significantly to axial torque production and that the flexed and twisted spine is less able to resist applied axial torques, possibly increasing the risk of torsional injury.     

Measurement of loads on the lumbar spine under isometric and isokinetic conditions

Ten male and ten female subjects were tested for their ability to exert maximal force about the lumbo-sacral junction (as is done during lifting) under controlled isometric and isokinetic conditions. The myoelectric activity of ten trunk muscles, intra-abdominal pressure, and torque produced by the back were monitored. There are prominent differences in the manner in which subjects utilize the musculature of the trunk for the production of torque statically and dynamically. A significant lag was identified between the onset of intra-abdominal pressure and torque, and this lag increased with increasing trunk velocity. These differences between isometric and isokinetic exertions suggest that isokinetic trunk testing provides a means of controlled evaluation that is appropriate for manual materials handling situations.     

Posture related to myoelectric silence of erectores spinae during trunk flexion

Electromyographic activity of erectores spinae exhibits points of abrupt change during trunk flexion from the erect position and return extension. This study examined the positions at which the myoelectric activity suddenly disappeared and later reappeared. Forty adults were investigated to define accurately the inclinations of the trunk, pelvis, and vertebral column at these positions. The positions at the commencement and cessation of the period of electrical silence both occurred at two-thirds of maximum trunk flexion (mean = 80 degrees +/- 13 degrees SD). At these positions, all flexion measurements were significantly less than their maxima (P less than 0.001). Hip flexion at the commencement of electrical silence was slightly above one-half its maximum range, and similar to the position at the recommencement of electrical activity (mean = 40 degrees +/- 12 degrees SD). The most reproducible measurement (r = 0.88) in both positions was vertebral flexion (89% Max.; mean = 48 degrees +/- 6 degrees SD). Eleven of the male subjects repeated the experimental task holding 10.1 kg in their hands. The effect of this was to produce inhibition and reactivation of erectores spinae at a greater degree of vertebral flexion.     

Effect of trunk flexion on cervical muscle EMG to rear impacts.

OBJECTIVE: To determine the effect of occupant positioning on the response of the cervical muscles to whiplash-type posterolateral impacts. METHODS: Twenty healthy volunteers underwent left posterolateral whiplash-type impacts with the volunteers seated "out-of-position". Electromyograms of the cervical muscles were recorded. RESULTS: Whether having the trunk flexed to the left or right at the time of impact, the muscle responses were low in magnitude, showing a trend to increasing EMG responses with increasing acceleration (P>0.05). The time to onset and time to peak electromyogram for most muscles showed a trend to progressively decrease with increasing levels of acceleration. With the subject flexed to the left, all muscles generated 31% or less of the maximal voluntary contraction electromyogram. With the subject flexed to the right, all muscles generated 27% or less of their maximal electromyogram. In both positions, the trapezii were the most active (P<0.05). Thus, having the trunk flexed out of neutral posture at the time of impact produces a very low magnitude cervical muscle response compared to impacts with the trunk in neutral posture. CONCLUSIONS: In the absence of bodily impact, the flexed trunk posture appears to produce a biomechanical response that would probably decrease the likelihood of cervical muscle injury in low velocity posterolateral impacts.     

Response of the flexion-relaxation phenomenon relative to the lumbar motion to load and speed

STUDY DESIGN: Nonrandomized control trial. OBJECTIVE: To determine if the variations of speed and loading conditions during trunk flexion-extension could influence the times of occurrence and disappearance of the electrical silence of the erector spinae muscles, the degrees of lumbar flexion at those instants, and the relative lumbar motion time. SUMMARY OF BACKGROUND DATA: It has been suggested that varying either the speed of movement or the load on the trunk during trunk flexion-extension movements may influence the flexion-relaxation phenomenon or the kinesiologic data. However, no study dealt with the simultaneous effect of the speed of movement on the spine rhythm and on the occurrence of the electrical silence of the erector spinae. METHODS: A total of 22 pain-free volunteers performed a series of trunk flexion-extension movements varying the speed and load. The motion of the lumbar spine ( degrees ) and the integrated electromyography (microV) of erector spinae muscles were simultaneously recorded. Two measures were calculated: the percentage of the maximum lumbar spine flexion at the instants when changes of electrical activity represented the beginning and end of the electrical silence and the relative lumbar spine motion time during trunk flexion and extension movements. RESULTS: The increase in speed of movement significantly increased the relative lumbar flexion time and significantly reduced the relative lumbar extension time (t = 2.49 and t = 2.25, P < 0.05); furthermore, it significantly delayed the appearance of the electrical silence in the range of flexion (t = 3.52, P < 0.01). There was no significant effect from a change in load. CONCLUSIONS: The relative spine motion time differed depending on the direction of movement, being longer during trunk flexion and shorter during extension. The increase in speed of movement produced greater differences in the relative time between trunk flexion and extension; furthermore, it delayed the appearance of the electrical silence of the erector spinae muscles in the range of flexion.     

Lumbar myoelectric spectral analysis for endurance assessment. A comparison of normals with deconditioned patients

A myoelectric protocol to objectively discriminate between test subjects based on trunk muscular performance differences (endurance) was investigated in a group of 11 healthy volunteers and ten industrial patients undergoing functional restoration for chronic disabling spinal disorders. The subjects performed a standardized exercise protocol, holding their upper torso unsupported for successive fixed-time trials while electromyographic (EMG) signals were recorded from erector spinae. A Fast Fourier Transform allowed calculation of the initial mean power frequency (MPF) for each trial. Isokinetic extensor trunk strength was independently measured at each session for comparison with myoelectric signal analysis. The investigation revealed significant differences in group statistics between patients in early rehabilitation and their subsequent tests, as well as between their initial test and the normal subject scores. However, test sensitivity for identifying patients with "low endurance" is questionable. There was no significant correlation between EMG initial MPF measures and isokinetic extensor trunk strength measures, even though all patients showed isokinetic improvement. Data suggest that the protocol used and myoelectric power spectrum temporal shifts may have some value for identification of individual subjects with endurance limitations (or fatigue resistance) in patients of this type. However, lack of a "gold standard" for comparison presents difficulties in documenting the value and validity with respect to endurance. The test may be of value to measure relative loads.     

Lumbar trunk muscle use in standing isometric heavy exertions

A study was conducted to see whether a biomechanical model previously validated for predicting the lumbar spine internal loads imposed by the performance of easy and moderately strenuous physical tasks was also adequate for predicting loads imposed by heavy exertions. Lumbar trunk muscle myoelectric activities were measured in 10 healthy young adult men performing a variety of less strenuous and more strenuous tasks while standing upright, and these were compared to the lumbar muscle contraction magnitudes predicted by the model. For the less strenuous tasks, measured activities and predicted forces showed strong linear correlations, confirming the validity of the model at those load levels. Model predictions for the more strenuous tasks were often found to be inadequate. Contrary to model-incorporated assumptions, substantial antagonistic muscle contractions sometimes occurred, intraabdominal pressurization may sometimes have contributed substantially to the maintenance of structural equilibrium, and the ligamentous tissues of the trunk seemed sometimes to develop substantial passive resistances to bending and twisting moments.     

In vivo measurements of the effect of whole body vibration on spinal loads

Purpose

It is assumed that whole body vibration (WBV) improves muscle strength, bone density, blood flow and mobility and is therefore used in wide ranges such as to improve fitness and prevent osteoporosis and back pain. It is expected that WBV produces large forces on the spine, which poses a potential risk factor for the health of the spine. Therefore, the aim of the study was to measure the effect of various vibration frequencies, amplitudes, device types and body positions on the loads acting on a lumbar vertebral body replacement (VBR).

Methods

Three patients suffering from a fractured lumbar vertebral body were treated using a telemeterized VBR. The implant loads were measured during WBV while the patients stood on devices with vertically and seesaw-induced vibration. Frequencies between 5 and 50 Hz and amplitudes of 1, 2 and 4 mm were tested. The patients stood with their knees straight, slightly bent, or bent at 60°. In addition, they stood on their forefeet.

Results

The peak resultant forces on the implant increased due to vibration by an average of 24 % relative to the forces induced without vibration. The average increase of the peak implant force was 27 % for vertically induced vibration and 15 % for seesaw vibration. The forces were higher when the legs were straight than when the knees were bent. Both the vibration frequency and the amplitude had only a minor effect on the measured forces.

Conclusions

The force increase due to WBV is caused by an activation of the trunk muscles and by the acceleration forces. The forces produced during WBV are usually lower than those produced during walking. Therefore, the absolute magnitude of the forces produced during WBV should not be harmful, even for people with osteoporosis.     

Correlation of objective measure of trunk motion and muscle function with low-back disability ratings

A study was undertaken to examine relations among some objective and subjective measures of low-back-related disability in a group of 41 low-back pain patients and in seven pain-free control subjects. Subjective measures of disability were obtained by Oswestry patient questionnaires. Oswestry disability score related significantly (P less than 0.001) to presence or absence of relaxation in back muscles during flexion. Mean trunk strength ratios were inversely related to disability score (P less than .05), and trunk mobility was meaningfully reduced (P less than .01). Despite loss of motion, a large enough excursion was observed to predict presence of back muscle relaxation. These findings imply that myoelectric signal levels, trunk strength ratios, and ranges of trunk motion may be used as objective indicators of low-back pain disability.     

The role of prerotation of the trunk in axial twisting efforts

The myoelectric activity of selected trunk muscles was recorded during the development of controlled isometric axial torques. Muscle activity was measured bilaterally over the erector spinae, the rectus abdominus, the oblique external and the oblique internal abdominal muscles at the L3 level. Subjects first applied graded isometric torque efforts over a 10 second ramp up to maximum voluntary contraction with the trunk in neutral rotation. They then repeated the effort with the trunk twisted to the left and right. The largest electromyographic activities were found in the agonistic oblique muscles, but considerable antagonistic activity was present also. While the activity of the internal oblique and rectus were bilaterally similar in symmetric standing a difference occurred between the two sides when the trunk was twisted to the right or left. Axial prerotation of the trunk by 30 degrees in the direction of torque development marginally decreased the maximal developed torque, whereas prerotation in the opposite direction increased the developed torque.     

Hand grip increases shoulder muscle activity: An EMG analysis with static handcontractions in 9 subjects

We examined 4 shoulder muscles-the supraspina-tus, infraspinatus, the middle portion of the deltoid and the descending part of the trapezius-with electromyography (EMG) in abducted and flexed arm positions, in 9 healthy subjects. the subjects were asked to produce a static handgrip force of 30% and 50% of maximal voluntary contraction (MVC) in 8 different arm positions. in all positions, the subjects held a dynamometer in the hand. the myoelectric activity in the shoulder muscles with only the dynamometer in the hand was compared to the EMG activity when static contractions were added. There was an association between static handgrip and shoulder muscle activity, as revealed by EMG. the EMG activity increased in the supraspinatus muscle in humeral flexion from and above 60° and in 120° abduction. in the infraspinatus muscle, the changes were less; a significant increase, however, was noticed in flexion. in the deltoid muscle there was a tendency towards increased activity in positions lower than 90°, in the higher arm positions, the activity decreased. There was no significant alteration regarding the EMG activity of the trapezius.

Our findings imply that high static handgrip force, particularly in elevated arm positions, increases the load on some shoulder muscles. the stabilizing muscles (the rotator cuff) were more influenced than the motor muscles by hand activity. Handgrip activity is important to evaluate while assessing shoulder load in manual work and in clinical evaluations of patients with shoulder pain.     

The Role of Decreased Hip IR as a Cause of Low Back Pain in a Golfer: a Case Report

Background

Among golf injuries, low back pain (LBP) is the most common compliant for both professional and amateur golfers. Hip rotational range of motion (ROM) might be related to LBP in those who repeatedly place specific activity rotational demands on the hip in one direction. Coordination of timing of movement (neural control) between the hip and lumbopelvic region during trunk movements is critical for normal mechanics. Altered timing can contribute to areas of high tissue loading and can lead to LBP symptoms seen during active lower limb movement tests. Patient was a 42-year-old male recreational golfer who presented with low back pain and decreased hip internal rotation ROM.

Methods

With the use of manual physical therapy to increase hip ROM and lumbar stabilization therapeutic exercises, the patient was able to return to pain-free golf and to better his handicap by three strokes.

Results

Significant improvement was seen in his Oswestry outcome score, and a (?) prone instability test was noted.

Conclusion

It is recommended to address hip ROM limitations in those experiencing low back pain while golfing. Rapid spinal rotation may produce large spinal loads, but this is likely not the major contributor to low back pain in golfers. Mechanical factors may play a larger role.