Homonymous and heteronymous reflex connections of the paraspinal muscles were investigated by the application of a tap to the muscle bellies of the lumbar multifidus and iliocostalis lumborum muscles and observation of surface electromyographic responses in the same muscles on both sides of the trunk. Reflexes were evoked in each of the homonymous muscles with latencies and estimated conduction velocities compatible with being evoked by Ia muscle afferents and having a monosynaptic component. Short latency heteronymous excitatory reflex connections were observed in muscles on the ipsilateral side, whilst reflex responses in the contralateral muscles were inhibitory in response to the same stimulus. The latencies of the crossed responses were on average 9.1 ms longer than the ipsilateral excitatory responses. These results are in contrast to the crossed excitatory responses observed between the abdominal muscles and trapezius muscles on the opposite aspect of the trunk. Such a difference in the reflex pathways between these two groups of trunk muscles compliments the different anatomical arrangement of the muscle groups and suggests a contribution to their commonly observed activation patterns.
Stretch reflex; Paraspinal muscles; Crossed reflex
Static trunk flexion working postures and disturbed trunk muscle reflexes are related to increased risk of low-back pain. Animal studies conclude that these factors may be related; passive tissue strain in spinal ligaments causes subsequent short-term changes in reflex. Although studies have documented changes in the myoelectric onset angle of flexion-relaxation following prolonged static flexion and cyclic flexion we could find no published evidence related to the human reflex response of the trunk extensor muscles following a period of static flexion-relaxation loading.
Eighteen subjects maintained static lumbar flexion for 15 min. Paraspinal muscle reflexes were elicited both before and after the flexion-relaxation protocol using pseudorandom stochastic force disturbances while recording EMG. Reflex gain was computed from the peak value of the impulse response function relating input force perturbation to EMG response using time-domain deconvolution analyses.
Reflexes showed a trend toward increased gain after the period of flexion-relaxation (P < 0.055) and were increased with trunk extension exertion (P < 0.021). Significant gender differences in reflex gain were observed (P < 0.01).
Occupational activities requiring extended periods of trunk flexion contribute to changes in reflex behavior of the paraspinal muscles. Results suggest potential mechanisms by which flexed posture work may contribute to low-back pain. Significant gender differences indicate risk analyses should consider personal factors when considering neuromuscular behavior.
Low-back; Reflex; Flexion-relaxation
Repeated measures experimental study of the effect of flexion-relaxation, recovery, and gender on paraspinal reflex dynamics.
To determine the effect of prolonged flexion-relaxation and recovery time on reflex behavior in human subjects.
Summary of Background Data.
Prolonged spinal flexion has been shown to disturb the paraspinal reflex activity in both animals and human beings. Laxity in passive tissues of the spine from flexion strain may contribute to desensitization of mechanoreceptors. Animal studies indicate that recovery of reflexes may take up to several hours. Little is known about human paraspinal reflex behavior following flexion tasks or the recovery of reflex behavior following the flexion tasks.
A total of 25 subjects performed static flexionrelaxation tasks. Paraspinal muscle reflexes were recorded before and immediately after flexion-relaxation and after a recovery period. Reflexes were quantified from systems identification analyses of electromyographic response in relation to pseudorandom force disturbances applied to the trunk.
Trunk angle measured during flexion-relaxation postures was significantly higher following static flexion-relaxation tasks (P < 0.001), indicating creep deformation of passive supporting structures in the trunk. Reflex response was diminished following flexion-relaxation (P < 0.029) and failed to recover to baseline levels during 16 minutes of recovery.
Reduced reflex may indicate that the spine is less stable following prolonged flexion-relaxation and, therefore, susceptible to injury. The absence of recovery in reflex after a substantial time indicates that increased low back pain risk from flexion-relaxation may persist after the end of the flexion task.
flexion-relaxation; reflex; low back; spine; electromyogram; stability
Involuntary responses to muscle stretch are often composed of a short-latency reflex (SLR) and more variable responses at longer latencies such as the medium-latency (MLR) and long-latency stretch reflex (LLR). Although longer latency reflexes are enhanced in the upper limb during stabilization of external loads, it remains unknown if they have a similar role in the lower limb. This uncertainty results in part from the inconsistency with which longer latency reflexes have been observed in the lower limb. A review of the literature suggests that studies that only observe SLRs have used perturbations with large accelerations, possibly causing a synchronization of motoneuron refractory periods or an activation of force-dependent inhibition. We therefore hypothesized that the amplitude of longer latency reflexes would vary with perturbation acceleration. We further hypothesized that if longer latency reflexes were elicited, they would increase in amplitude during control of an unstable load, as has been observed in the upper limb. These hypotheses were tested at the ankle while subjects performed a torque or position control task. SLR and MLR reflex components were elicited by ankle flexion perturbations with a fixed peak velocity and variable acceleration. Both reflex components initially scaled with acceleration, however, while the SLR continued to increase at high accelerations, the MLR weakened. At accelerations that reliably elicited MLRs, both the SLR and MLR were reduced during control of the unstable load. These findings clarify the conditions required to elicit MLRs in the ankle extensors and provide additional evidence that rapid feedback pathways are downregulated when stability is compromised in the lower limb.
Acceleration; ankle; long-latency reflex; stability
The effect of posture on the EMG pattern of the normal auditory startle reflex was investigated. The startle response to an unexpected auditory tone was studied in eleven normal subjects when standing, and in six normal subjects when sitting relaxed or tonically plantar flexing both feet. Reflex EMG activity was recorded in the tibialis anterior and soleus about twice as frequently when standing, than when sitting relaxed. In addition, the median latencies to onset of reflex EMG activity in the tibialis anterior and soleus were about 40 and 60 ms shorter during standing, than when sitting relaxed. No short latency EMG activity was recorded in the calf muscles during tonic plantar flexion of the feet, while sitting. The effect of posture on the EMG pattern of the pathological auditory startle reflex was studied in five patients with hyperekplexia. In three patients the latency to onset of reflex EMG activity in the tibialis anterior was shorter when standing, than when sitting relaxed. The EMG pattern of the reflex response to sound was studied in detail in two of these patients and consisted of up to three successive components. The expression of each EMG component depended on the postural set of the limbs. In particular, a distinct short latency component was found in posturally important muscles following auditory stimulation. This short latency component was not recorded when sitting relaxed. It is concluded that the EMG pattern of the physiological and pathological auditory startle response is not fixed, but may change with the postural stance of the body. This finding supports the theory that the normal startle reflex and the abnormal startle reflex in hyperekplexia have a common brainstem origin.
Electromyographic responses of triceps surae and tibialis anterior produced by dorsiflexion stretch were studied in 17 patients with Parkinson's disease. Most patients showed increased muscular activity when attempting to relax. A few patients showed an increase of short-latency reflexes when relaxed and when exerting a voluntary plantarflexion prior to the stretch. Many patients showed long-latency reflexes when relaxed and all but one showed long-latency reflexes with voluntary contraction; and these reflexes were often larger in magnitude and longer in duration than those seen in normal subjects. Unlike the short-latency reflex, the long-latency reflex did not disappear with vibration applied to the Achilles tendon. The long-latency reflexes and continuous responses to slow ramp stretches were diminished at a latency similar to the beginning of long-latency reflexes when the stretching was quickly reversed. Dorsiflexion stretch also frequently produced a shortening reaction in tibialis anterior. Of all the abnormal behavior exhibited by the Parkinsonian patients only the long-latency reflex magnitude and duration correlated with the clinical impression of increased tone. The mechanism of the long-latency reflex to stretch which is responsible for rigidity is not certain, but the present results are consistent with a group II mediated tonic response.
Context: Ankle braces may enhance ankle joint proprioception, which in turn may affect reflexive ankle muscle activity during a perturbation. Despite the common occurrence of plantar-flexion inversion ankle injuries, authors of previous studies of ankle muscle latencies have focused on inversion stresses only.
Objective: To examine the latency of the peroneus longus (PL), peroneus brevis (PB), and tibialis anterior (TA) muscles in response to various degrees of combined plantar-flexion and inversion stresses in braced and unbraced asymptomatic ankles.
Design: Repeated measures.
Setting: University biomechanics laboratory.
Patients or Other Participants: Twenty-eight healthy females and 12 healthy males (n = 40: mean age = 23.63 years, range = 19 to 30 years; height = 172.75 ± 7.96 cm; mass = 65.53 ± 12.0 kg).
Intervention(s): Participants were tested under 2 conditions: wearing and not wearing an Active Ankle T1 brace while dropping from a custom-made platform into 10°, 20°, and 30° of plantar flexion and 30° of inversion.
Main Outcome Measure(s): The time between platform drop and the onset of PL, PB, and TA electromyographic activity was measured to determine latencies. We calculated a series of 2-way analyses of variance to determine if latencies were different between the conditions (braced and unbraced) and among the plantar-flexion angles (α = .05).
Results: No interaction was found between condition and plantar-flexion angle. No significant main effects were found for condition or plantar-flexion angle. Overall means for braced and unbraced conditions were not significantly different for each muscle tested. Overall means for angle for the PL, PB, and TA were not significantly different.
Conclusions: Reflexive activity of the PL, PB, or TA was unaffected by the amount of plantar flexion or by wearing an Active Ankle T1 brace during an unanticipated plantar-flexion inversion perturbation.
ankle injuries; lower extremity; biomechanics; orthoses; reaction time
H-reflexes of the flexor carpi radialis muscle were studied in 52 controls and 25 cancer patients with radiation-induced brachial plexopathy. It was found that H-reflex conduction velocity (H-RCV) decreased with increasing age. This was not true for H-reflex latency (H-RL) and inter-latency times. There were no H-RCV and latency differences between age-matched male and female subjects. In the affected arm the reflex was absent in nine patients and delayed in 16 patients in whom H-RCV was decreased in 13 patients. Three patients showed large H-RL differences which were also notable features in median nerve disease in the region of the brachial plexus.
Knee surgery may alter the neuromuscular response to unexpected perturbations during functional, dynamic tasks. Long latency reflexes (LLR) follow a transcortical pathway and appear to be modifiable by task demands, potentially giving them a role in neuromuscular performance. We examined LLRs of the quadriceps and hamstrings in response to unexpected perturbations in individuals with a repaired anterior cruciate ligament (ACLR) during a weight-bearing task. We also investigated the anticipatory and volitional muscle activity that preceded and followed the LLR to quantify possible reflex adaptations associated with surgical repair.
Twelve females with ACLR and twelve healthy female controls performed a single leg squat maneuver, tracking a sinusoidal target. Random perturbations at the start of the flexion phase yielded tracking errors (“overshoot errors”) and triggered compensatory reflex activity.
ACLR subjects demonstrated greater overshoot error and knee velocity during unexpected perturbations, increased LLR responses, and reduced absolute anticipatory, short-latency reflex, and voluntary quadriceps activity.
ACLR subjects showed impaired response to perturbation and a distinct EMG profile during a dynamic single leg weight-bearing task. Future research will determine the cause of neural adaptations in those with ACLR.
Neuromuscular adaptations may be a viable target for post-ACL injury rehabilitation interventions.
neuromuscular control; single leg squat; weight bearing; reflexes
By perianal electrical stimulation and EMG recording from the external anal sphincter the anal reflex was constantly present in normal subjects. The latency decreased within certain limits with increasing stimulation to an average minimum latency of 50 ms (SD 10.5). There was no difference between the minimum latency in normal subjects and patients with suprasegmental lesions of the CNS. The latency may be prolonged in patients with lesion of the reflex arc. By stimulation over the posterior tibial nerve behind the medial malleolus a reflex reaction could be picked up constantly from the anal sphincter in normal subjects. This reflex had a longer latency but a lower threshold than the reflex reaction from the tibialis anterior muscle. The average minimum latency from the anal sphincter was 93 ms (SD 21.1) and from the tibialis anterior muscle 64 ms (SD 7.9). In the absence of the anal reflex it may be possible to localise the defect to the afferent or efferent parts of the reflex by using types of stimulation. Preliminary studies of spinal shock revealed a perianally elicited anal reflex in all cases, but also a response to peripheral stimulation in some of the cases, more frequently found in the anal sphincter than in the tibialis anterior muscle.
The high risk of sustaining subsequent vertebral fractures after an initial fracture cannot be explained solely by low bone mass. Extra-osseous factors, such as neuromuscular characteristics may help to explain this clinical dilemma. Elderly women with (n = 11) and without (n = 14) osteoporotic vertebral fractures performed rapid shoulder flexion to perturb the trunk while standing on a flat and short base. Neuromuscular postural responses of the paraspinal muscles at T6 and T12, and deep lumbar multifidus at L4 were recorded using intramuscular electromyography (EMG). Both groups demonstrated bursts of EMG that were initiated either before or shortly after the onset of shoulder flexion (P < 0.05). Paraspinal and multifidus onset occurred earlier in the non-fracture group (50–0 ms before deltoid onset) compared to the fracture group (25 ms before and 25 ms after deltoid onset) in the flat base condition. In the short base condition, EMG amplitude increased significantly above baseline earlier in the non-fracture group (75–25 ms before deltoid onset) compared to the fracture group (25–0 ms before deltoid onset) at T6 and T12; yet multifidus EMG increased above baseline earlier in the fracture group (50–25 ms before deltoid) compared to the non-fracture group (25–0 ms before deltoid). Time to reach maximum amplitude was shorter in the fracture group. Hypothetically, the longer time to initiate a postural response and shorter time to reach maximum amplitude in the fracture group may indicate a neuromuscular contribution towards subsequent fracture aetiology. This response could also be an adaptive characteristic of the central nervous system to minimise vertebral loading time.
Osteoporosis; Vertebral fracture; Paraspinal muscle; Electromyography; Neuromuscular control
Objectives: To compare the MAS with objective neurophysiological tests of spasticity.
Methods: The MAS was recorded in patients with post-stroke lower limb muscle spasticity and correlated with the excitability of the α motor neurones. The latter was evaluated by measuring the latency of the Hoffmann reflex (H reflex) and the ratio of the amplitude of the maximum H reflex (Hmax) to that of the compound action motor potential of the soleus muscle (Mmax).
Results: Data on 24 randomly recruited patients were analysed. Patients were divided into two groups according to their MAS score: 14 had a MAS score of 1 (group A) and 10 scored 2 (group B). The two groups were comparable with respect to age and sex, but in group A there was a longer period since the stroke. The H reflex latency was reduced and the Hmax:Mmax ratio was increased in both groups. The Hmax:Mmax ratio values were higher for group B but the differences were not statistically significant.
Conclusions: There is a relation between the MAS scores and α motor neurone excitability, although it is not linear. This suggests that the MAS measures muscle hypertonia rather than spasticity.
Vibration is known to alter proprioceptive afferents and create a tonic vibration reflex. The control of force and its variability are often considered determinants of motor performance and neuromuscular control. However, the effect of vibration on paraspinal muscle control and force production remains to be determined.
Twenty-one healthy adults were asked to perform isometric trunk flexion and extension torque at 60% of their maximal voluntary isometric contraction, under three different vibration conditions: no vibration, vibration frequencies of 30 Hz and 80 Hz. Eighteen isometric contractions were performed under each condition without any feedback. Mechanical vibrations were applied bilaterally over the lumbar erector spinae muscles while participants were in neutral standing position. Time to peak torque (TPT), variable error (VE) as well as constant error (CE) and absolute error (AE) in peak torque were calculated and compared between conditions.
The main finding suggests that erector spinae muscle vibration significantly decreases the accuracy in a trunk extension isometric force reproduction task. There was no difference between both vibration frequencies with regard to force production parameters. Antagonist muscles do not seem to be directly affected by vibration stimulation when performing a trunk isometric task.
The results suggest that acute erector spinae muscle vibration interferes with torque generation sequence of the trunk by distorting proprioceptive information in healthy participants.
Muscle vibration; Muscle spindle; Low back; Neuromuscular responses; Isometric force; Proprioception; Erector spinae muscles
Although the soleus (Sol), medial gastrocnemius (MG), and lateral gastrocnemius (LG) muscles differ in function, composition, and innervations, it is a common practice is to investigate them as single H-reflex recording. The purpose of this study was to compare H-reflex recordings between these three sections of the triceps surae muscle group of healthy participants while lying and standing during three different ankle positions.
The Sol, MG and LG muscles' H-reflexes were recorded from ten participants during prone lying and standing with the ankle in neutral, maximum dorsiflexion, and maximum plantarflexion positions. Four traces were averaged for each combination of conditions. Three-way ANOVAs (posture X ankle position X muscle) with planned comparisons were used for statistical comparisons.
Although the H-reflex in the three muscle sections differed in latency and amplitude, its dependency on posture and ankle position was similar. The H-reflex amplitudes and maximum H-reflex to M-response (H/M) ratios were significantly 1) lower during standing compared to lying with the ankle in neutral, 2) greater during standing with the ankle in plantarflexion compared to neutral, and 3) less with the ankle in dorsiflexion compared to neutral during lying and standing for all muscles (p ≤ .05).
Varying demands are required for muscles activated during distinctly different postures and ankle movement tasks.
Based on our clinical experience, the H-reflex amplitude asymmetry might be an earlier sign of nerve root involvement than latency in patients with S1 radiculopathy. However, no data to support this assumption are available. The purpose of this study was to review and report the electrophysiological changes in H-reflex amplitude and latency in patients with radiculopathy in order to determine if there is any evidence to support the assumption that H-reflex amplitude is an earlier sign of nerve root involvement than latency.
Patients with radiculopathy showed significant amplitude asymmetry when compared with healthy controls. However, latency was not always significantly different between patients and healthy controls. These findings suggest nerve root axonal compromise that reduced reflex amplitude earlier than the latency parameter (demyelination) during the pathologic processes.
Contrary to current clinical thought, H-reflex amplitude asymmetry is an earlier sign/parameter of nerve root involvement in patients with radiculopathy compared with latency.
Spinal stability is related to both the intrinsic stiffness of active muscle as well as neuromuscular reflex response. However, existing analyses of spinal stability ignore the role of the reflex response, focusing solely on the intrinsic muscle stiffness associated with voluntary activation patterns in the torso musculature. The goal of this study was to empirically characterize the role of reflex components of spinal stability during voluntary trunk extension exertions. Pseudorandom position perturbations of the torso and associated driving forces were recorded in 11 healthy adults. Nonlinear systems-identification analyses of the measured data provided an estimate of total systems dynamics that explained 81% of the movement variability. Proportional intrinsic response was less than zero in more than 60% of the trials, e.g. mean value of PINT during the 20% maximum voluntary exertion trunk extension exertions 415±354 N/m. The negative value indicated that the intrinsic muscle stiffness was not sufficient to stabilize the spine without reflex response. Reflexes accounted for 42% of the total stabilizing trunk stiffness. Both intrinsic and reflex components of stiffness increased significantly with trunk extension effort. Results reveal that reflex dynamics are a necessary component in the stabilizing control of spinal stability.
Low-back; Spine; Stability; Reflex; Stiffness
The flexion reflex can be elicited via stimulation of skin, muscle, and high-threshold afferents inducing a generalized flexion of the limb. In spinalized animal models this reflex is quite prominent and is strongly modulated by actions of hip proprioceptors. However, analogous actions on the flexion reflex in spinal cord injured (SCI) humans have not yet been examined. In this study, we investigated the effects of imposed static hip angle changes on the flexion reflex in ten motor incomplete SCI subjects when input from plantar cutaneous mechanoreceptors was also present. Flexion reflexes were elicited by low-intensity stimulation of the sural nerve at the lateral malleolus, and were recorded from the ipsilateral tibialis anterior (TA) muscle. Plantar skin stimulation was delivered through two surface electrodes placed on the metatarsals, and was initiated at different delays ranging from 3 to 90 ms. We found that non-noxious sural nerve stimulation induced two types of flexion reflexes in the TA muscle, an early, and a late response. The first was observed only in three subjects and even in these subjects, it appeared irregularly. In contrast, the second (late) flexion reflex was present uniformly in all ten subjects and was significantly modulated during hip angle changes. Flexion reflexes recorded with hip positioned at different angles were compared to the associated control reflexes recorded with hip flexed at 10°. Hip flexion (30°, 40°) depressed the late flexion reflex, while no significant effects were observed with the hip set in neutral angle (0°). Strong facilitatory effects on the late flexion reflex were observed with the hip extended to 10°. Moreover, the effects of plantar skin stimulation on the flexion reflex were also found to depend on the hip angle. The results suggest that hip proprioceptors and plantar cutaneous mechanoreceptors strongly modulate flexion reflex pathways in chronic human SCI, verifying that this type of sensory afferent feedback interact with spinal interneuronal circuits that have been considered as forerunners of stepping and locomotion. The sensory consequences of this afferent input should be considered in rehabilitation programs aimed to restore movement and sensorimotor function in these patients.
Cutaneous afferents; Flexion reflex; Hip proprioceptors; Rehabilitation; Sensorimotor integration
Context: Greater musculotendinous stiffness may enhance spinal stretch reflex sensitivity by improving mechanical coupling of the muscle spindle and the stretch stimulus. This heightened sensitivity would correspond with a shorter latency and higher-amplitude reflex response, potentially enhancing joint stability.
Objective: To compare spinal stretch reflex latency and amplitude across groups that differed in musculotendinous stiffness.
Design: Static group comparisons.
Setting: Research laboratory.
Patients or Other Participants: Forty physically active individuals (20 men, 20 women).
Intervention(s): We verified a sex difference in musculotendinous stiffness and compared spinal stretch reflex latency and amplitude in high-stiffness (men) and low-stiffness (women) groups. We also evaluated relationships between musculotendinous stiffness and spinal stretch reflex latency and amplitude, respectively.
Main Outcome Measure(s): Triceps surae musculotendinous stiffness and soleus spinal stretch reflex latency and amplitude were assessed at 30% of a maximal voluntary isometric plantar-flexion contraction.
Results: The high-stiffness group demonstrated significantly greater stiffness (137.41 ± 26.99 N/cm) than the low-stiffness group did (91.06 ± 20.10 N/cm). However, reflex latency (high stiffness = 50.11 ± 2.07 milliseconds, low stiffness = 48.26 ± 2.40 milliseconds) and amplitude (high stiffness = 0.28% ± 0.12% maximum motor response, low stiffness = 0.31% ± 0.16% maximum motor response) did not differ significantly across stiffness groups. Neither reflex latency (r = .053, P = .746) nor amplitude (r = .073, P = .653) was related significantly to musculotendinous stiffness.
Conclusions: A moderate level of pretension (eg, 30%) likely eliminates series elastic slack; thus, a greater change in force per unit-of-length change (ie, heightened stiffness) would have minimal effects on coupling of the muscle spindle and the stretch stimulus and, therefore, on spinal stretch reflex sensitivity. It appears unlikely that differences in musculotendinous stiffness influenced spinal stretch reflex sensitivity when initiated from a moderate level of pretension. Consequently, differences in musculotendinous stiffness did not appear to influence dynamic joint stability with respect to reflexive neuromuscular control.
latency; amplitude; material modulus; compliance; neuromuscular control
The motor disorders associated with human spasticity arise, partly from a pathological increase in the excitability of muscle stretch reflexes. In clinical practice, reflex excitability is commonly assessed by grading the reflex response to a blow delivered to the tendon of a muscle. This is a much simpler response than the complex patterns of activity which may be elicited following muscle stretch caused by active or passive movement. Changes in the biceps brachii tendon jerk response have been followed over the first year after stroke in a group of hemiparetic patients and compared with changes in short and medium latency reflex responses elicited by imposed elbow flexion of initially relaxed spastic muscle and with the development of the late reflex responses which contribute to spastic hypertonia. A progressive increase in tendon jerk responses occurred over the first year following stroke, whereas reflex responses to imposed displacement, in particular the late reflex responses contributing to muscle hypertonia, reached their peak excitability one to three months after stroke, with a subsequent reduction in activity. The tendon jerk reflex therefore provides an incomplete picture of the pathological changes in the reflex responses in spasticity.
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.
Twenty-seven healthy adults performed flexion-extension tasks under 4 different experimental conditions: no fatigue/no load, no fatigue/load, fatigue/no load, and fatigue/load. Total flexion angle corresponding to the onset and cessation of myoelectric silence, hip flexion angle, lumbar flexion angle and maximal trunk flexion angle were compared across different experimental conditions by 2 × 2 (Load × Fatigue) repeated-measures ANOVA.
The angle corresponding to the ES onset of myoelectric silence was reduced after the fatigue task, and loading the spine decreased the lumbar contribution to motion compared to the hip during both flexion and extension. A relative increment of lumbar spine motion compared to pelvic motion was also observed in fatigue conditions.
Previous results suggested that ES muscles, in a state of fatigue, are unable to provide sufficient segmental stabilization. The present findings indicate that, changes in lumbar-stabilizing mechanisms in the presence of muscle fatigue seem to be caused by modulation of lumbopelvic kinematics.
Fick hypothesized in 1911 that the erector spinae muscles are not active when the trunk is in the fully flexed position. This effect was later called the flexion-relaxation phenomenon (FRP) and is believed to be the result of the ligaments and other passive elements of the spine taking over the load of the muscles. This study examined the effect of loading on the EMG activity of five males and five females during postures of standing at 45 degrees, 90 degrees, and full flexion. The results showed major differences in the relationship between the electromyographic signal (EMG) of the erector spinae and loading for the four postures. The erector spinae muscles did not activate in positions of full flexion (or even 90 degrees for some subjects) for loading as high as 50% of their maximum voluntary contraction, suggesting that alternative muscles are being activated and that the passive tissues may be put under higher loads than originally thought in these positions. The results suggested that the FRP could be used as a biofeedback tool to illustrate to workers that their muscles are not turning on in the fully flexed positions, and therefore, these positions should be avoided.
The purpose of this study was to determine differences in the timing of postural reflexes and changes in kinematics between those who fell (Fallers) in response to standing platform translations and those who did not (Non-fallers). Forty-four persons with stroke were exposed to unexpected forward and backward platform translations while standing. Surface electromyography from bilateral tibialis anterior, gastrocnemius, rectus femoris, and biceps femoris were recorded along with kinematic data. Those that fell in response to the translations were compared to those who did not fall in terms of (1) postural reflex onset latency, (2) the time interval between the activation of distal and proximal muscles (i.e. intralimb coupling), and (3) changes in joint angles and trunk motion. Approximately 85% of falls occurred in response to the forward translations. Postural reflex onset latencies were delayed and intralimb coupling durations were longer in the Faller versus Non-faller group. At the time that the platform completed the translating motion (300 ms), the Faller group demonstrated higher trunk velocity, greater change in paretic ankle angle, and the trunk was further behind the ankle compared to the Non-faller group. This study suggests that following platform translations, delays in the timing of postural reflexes and disturbed intralimb coupling result in changes in kinematics, which contribute to falls in persons with stroke.
PMID: 16418855 CAMSID: cams1999
falls; cerebrovascular accident; reflex; perturbation; postural control
Clinical electrophysiological studies were analysed in 60 consecutive patients with back pain with or without other evidence for a radiculopathy. These studies included needle EMG of relevant limb and paraspinal muscles as well as F responses and H reflexes recorded from the soleus muscle. Segmental denervation was found in 29 of the 60 patients. In 57 patients, abnormal slowing of the F response was present in 27, either unilaterally (25) or bilaterally (two). In 18 of 47 patients with H reflex studies, the H reflex was either unilaterally absent (12), asymmetrically prolonged (five), or bilaterally prolonged (one). Statistically significant (P less than 0.05) associations were found between (1) abnormalities of H reflexes and F responses, (2) F response slowing and radicular injury shown by EMG, (3) segmentally consistent radiographic defects and abnormalities of both H reflexes and F responses, and (4) depressed Achilles reflexes as well as sensory loss and abnormal H reflexes. No significant association, however, was present between abnormalities of EMG, F responses, or H reflexes and pain radiation by history or positive straight leg-raising tests. These data suggest that pain in radicular syndromes is related to the functioning of smaller afferent fibres.
Using a Cybex® trunk extension/flexion device, we measured the effects of rigid and semirigid lumbar/sacral supports on peak muscular torque, total work, and average power. Ten well-conditioned men, aged 21 to 35, performed three testing sessions each at 7-day intervals (one session with a rigid support, one session with a semirigid support, and one with no support). We selected four isokinetic testing speeds (30°/s, 60°/s, 90°/s, and 120°/s), complying with a standard Cybex trunk extension/flexion protocol. Differences between lumbar/sacral supports were analyzed using an analysis of variance (ANOVA) and Scheffé post hoc tests. Peak torque, total work, and average power were significantly different (p<.05) during trunk flexion at various isokinetic velocities. Trunk extension movements did not appear to be affected by the use of supports, but trunk flexion was significantly greater with the semirigid device and with no device than with the rigid support. We concluded that a rigid lumbar/sacral support decreases strength during movement tasks involving trunk flexion with resistance.
Clinicians may obtain false-negative Lachman tests for tibial displacement when the trunk position of the athlete varies as the anterior cruciate ligament injury is assessed on the field, on the sideline, and in the clinic. We examined the influence of supine, semireclined, and sitting trunk positions on arthrometric laxity measurements of the knee.
Design and Setting:
Subjects in the 3 trunk-thigh test positions (15 °, 45 °, and 90 ° of hip flexion) were passively supported and tested in a counterbalanced order. The right knee was maintained at 29.0 ° ± 3.1 ° of flexion. A 133-N (30-1b) anterior force was applied to the right knee using a modified KT-1000 knee arthrometer equipped with a strain gauge that allowed for digital display of the displacement force.
Ten males and 5 females without present knee injury or history of knee ligament repair to the right lower extremity.
Three tibial displacement (mm) trials at each trunk position were averaged and used for analysis.
A 1-factor (trunk-thigh position) repeated-measures analysis of variance revealed no significant difference in anterior tibial displacement values among the 3 trunk-thigh positions (P > .05). Group means for displacement were 7.9 ± 2.3 mm (supine), 8.1 ± 2.5 mm (semireclined), and 8.3 ± 2.6 mm (sitting).
These findings suggest that alterations in trunk position are not a problem in the instrumented assessment of anterior tibial displacement in an uninjured population. Further research should determine the relevance of these findings, as well as “end-feel” (ie, stiffness) in subjects with injury to the anterior cruciate ligament. Further research should also determine if these findings can be applied when comparing passive versus active (eg, propped on elbows or hands) trunk support in subjects with anterior cruciate ligament-injured knees.
knee; arthrometer; Lachman test; anterior cruciate ligament; laxity