Associations between Measures of Structural Morphometry and Sensorimotor Performance in Individuals with Nonspecific Low Back Pain.

BACKGROUND AND PURPOSE: To date, most structural brain imaging studies in individuals with nonspecific low back pain have evaluated volumetric changes. These alterations are particularly found in sensorimotor-related areas. Although it is suggested that specific measures, such as cortical surface area and cortical thickness, reflect different underlying neural architectures, the literature regarding these different measures in individuals with nonspecific low back pain is limited. Therefore, the current study was designed to investigate the association between the performance on a sensorimotor task, more specifically the sit-to-stand-to-sit task, and cortical surface area and cortical thickness in individuals with nonspecific low back pain and healthy controls. MATERIALS AND METHODS: Seventeen individuals with nonspecific low back pain and 17 healthy controls were instructed to perform 5 consecutive sit-to-stand-to-sit movements as fast as possible. In addition, T1-weighted anatomic scans of the brain were acquired and analyzed with FreeSurfer. RESULTS: Compared with healthy controls, individuals with nonspecific low back pain needed significantly more time to perform 5 sit-to-stand-to-sit movements (P < .05). Brain morphometric analyses revealed that cortical thickness of the ventrolateral prefrontal cortical regions was increased in patients with nonspecific low back pain compared with controls. Furthermore, decreased cortical thickness of the rostral anterior cingulate cortex was associated with lower sit-to-stand-to-sit performance on an unstable support surface in individuals with nonspecific low back pain and healthy controls (r = -0.47, P < .007). In addition, a positive correlation was found between perceived pain intensity and cortical thickness of the superior frontal gyrus (r = 0.70, P < .002) and the pars opercularis of the inferior ventrolateral prefrontal cortex (r = 0.67, P < .004). Hence, increased cortical thickness was associated with increased levels of pain intensity in individuals with nonspecific low back pain. No associations were found between cortical surface area and the pain characteristics in this group. CONCLUSIONS: The current study suggests that cortical thickness may contribute to different aspects of sit-to-stand-to-sit performance and perceived pain intensity in individuals with nonspecific low back pain.

Effect of slow, small movement on the vibration-evoked kinesthetic illusion.

The study reported in this paper investigated how vibration-evoked illusions of joint rotation are influenced by slow (0.3 degrees /s), small (2-4 degrees ) passive rotation of the joint. Normal human adults (n=15) matched the perceived position of the left ("reference") arm with the right ("matching") arm while vibration (50 pps, 0.5 mm) was applied for 30 s to the relaxed triceps brachii of the reference arm. Both arms were constrained to rotate horizontally at the elbow. Three experimental conditions were investigated: (1) vibration of the stationary reference arm, (2) slow, small passive extension or flexion of the reference arm during vibration, and (3) slow, small passive extension or flexion of the reference arm without vibration. Triceps brachii vibration at 50 pps induced an illusion of elbow flexion. The movement illusion began after several seconds, relatively fast to begin with and gradually slowing down to a stop. On average, triceps vibration produced illusory motion at an average latency of 6.3 s, amplitude of 9.7 degrees , velocity of 0.6 degrees /s, and duration of 16.4 s. During vibration, slow, small ( approximately 0.3 degrees /s, 1.3 degrees ) passive rotations of the joint dramatically enhanced, stopped, or reversed the direction of illusory movement, depending on the direction of the passive joint rotation. However, the subjects' perceptions of these passive elbow rotations were exaggerated: 2-3 times the size of the actual movement. In the absence of vibration, the subjects accurately reproduced these passive joint rotations. We discuss whether the exaggerated perception of slow, small movement during vibration is better explained by contributions of non muscle spindle Ia afferents or by changes in the mechanical transmission of vibration to the receptor.

The sit-up: complex kinematics and muscle activity in voluntary axial movement.

This paper describes the kinematics and muscle activity associated with the standard sit-up, as a first step in the investigation of complex motor coordination. Eight normal human subjects lay on a force table and performed at least 15 sit-ups, with the arms across the chest and the legs straight and unconstrained. Several subjects also performed sit-ups with an additional weight added to the head. Support surface forces were recorded to calculate the location of the center of pressure and center of gravity; conventional motion analysis was used to measure segmental positions; and surface EMG was recorded from eight muscles. While the sit-up consists of two serial components, 'trunk curling' and 'footward pelvic rotation', it can be further subdivided into five phases, based on the kinematics. Phases I and II comprise trunk curling. Phase I consists of neck and upper trunk flexion, and phase II consists of lumbar trunk lifting. Phase II corresponds to the point of peak muscle contraction and maximum postural instability, the 'critical point' of the sit-up. Phases III-V comprise footward pelvic rotation. Phase III begins with pelvic rotation towards the feet, phase IV with leg lowering, and phase V with contact between the legs and the support surface. The overall pattern of muscle activity was complex with times of EMG onset, peak activity, offset, and duration differing for different muscles. This complex pattern changed qualitatively from one phase to the next, suggesting that the roles of different muscles and, as a consequence, the overall form of coordination, change during the sit-up.

The effect of aging on dynamic position sense at the ankle.

The present study addressed whether dynamic position sense at the ankle--or sense of position and velocity during movement--shows a similar decline as a result of aging as previously described for static position sense and movement detection threshold. Additionally, the involvement of muscle spindle afferents in the possible age-related decline was studied. To assess dynamic position sense, blindfolded subjects had to open the hand briskly when the right ankle was rotating passively through a prescribed target angle. To assess the involvement of muscle spindles, the effect of tibialis anterior vibration was studied. The results showed that aging lead to a significant increase in deviation from the target angle at hand opening as well as in variability of performance. Vibration resulted in larger undershoot errors in the elderly compared to the young adults, suggesting that the age-related decline in performance on the dynamic position sense task is not (solely) due to muscle spindle function changes. Alternatively, this degeneration might be due to altered input from other sources of proprioceptive input, such as skin receptors. The elderly subjects did show a beneficial effect of practice with the task, which may provide solid fundaments for rehabilitation.

Coexistence of stability and mobility in postural control: evidence from postural compensation for respiration.

This study evaluated the extent to which movement of the lower limbs and pelvis may compensate for the disturbance to posture that results from respiratory movement of the thorax and abdomen. Motion of the neck, pelvis, leg and centre of pressure (COP) were recorded with high resolution in conjunction with electromyographic activity (EMG) of flexor and extensor muscles of the trunk and hip. Respiration was measured from ribcage motion. Subjects breathed quietly, and with increased volume due to hypercapnoea (as a result of breathing with increased dead-space) and a voluntary increase in respiration. Additional recordings were made during apnoea. The relationship between respiration and other parameters was measured from the correlation between data in the frequency domain (i.e. coherence) and from time-locked averages triggered from respiration. In quiet standing, small angular displacements ( approximately 0.5 degrees ) of the trunk and leg were identified in raw data. Correspondingly, there were peaks in the power spectra of the angular movements and EMG. While body movement and EMG were coherent with respiration (>0.5), the coherence between respiration and COP displacement was low (<0.2). The amplitude of movement and coherence was increased when respiration was increased. The present data suggest that the postural disturbance that results from respiratory movement is matched, at least partly, and counteracted by small angular displacements of the lower trunk and lower limbs. Thus, stability in quiet stance is dependent on movement of multiple body segments and control of equilibrium cannot be reduced to control of a single joint.

Study of differences in peripheral muscle strength of lean versus obese women: an allometric approach.

OBJECTIVE: To investigate whether peripheral muscle strength is significantly different between lean and obese women controlled for age and physical activity, using an allometric approach. DESIGN: Cross-sectional study of isometric handgrip and isokinetic leg and trunk muscle strength. SUBJECTS: 173 obese (age 39.9+/-11.4 y, body mass index (BMI) 37.8+/-5.3 kg/m(2)) and 80 lean (age 39.7+/-12.2 y, BMI 22.0+/-2.2 kg/m(2)) women. MEASUREMENTS: Anthropometric measures (weight, height) and body composition (bioelectrical impedance method), isometric handgrip (maximal voluntary contraction on the Jamar dynamometer), isokinetic trunk flexion-extension, trunk rotation, and knee flexion-extension (Cybex dynamometers). RESULTS: Absolute isokinetic strength output (that is, strength uncorrected for fat-free mass) was larger in obese compared to lean women, except for knee flexion and isometric handgrip, which were not significantly different (P>0.05). Pearson correlation coefficients between strength measures and fat-free mass (kg) were low to moderate both in lean (r=0.28-0.53, P<0.05) and in obese (r=0.29-0.49, P<0.001) women. There was no correlation with fat mass (kg) in the lean, whereas in the obese women a weak positive relation could be observed for most isokinetic data (r=0.21-0.39, P<0.01). When correcting for fat-free mass (raised to the optimal exponent determined by allometric scaling), all strength measurements were at least 6% lower in obese when compared to the lean women, except for trunk flexion, which was at least 8% stronger in obese women. DISCUSSION: The higher absolute knee extension strength measures of leg and the similar extension strength of the trunk in the obese sample compared to the lean might be explained by the training effect of weight bearing and support of a larger body mass. However when the independent effect of fat-free mass is removed, these strength measures, as well as oblique abdominal muscle and handgrip strength, turned out to be lower in obese women. These observations could be the reflection of the overall impairment of physical fitness as a consequence of obesity and its metabolic complications.

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

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

Lumbosacral repositioning accuracy in standing posture: a combined electrogoniometric and videographic evaluation.

OBJECTIVE: To provide a new method of measuring repositioning accuracy in the lumbosacral spine in a standing position. DESIGN: A test-retest and parallel-forms reliability testing was performed. BACKGROUND: The contribution of proprioception to lumbar muscle function and to the stability of the lumbar spine is relatively unknown. METHOD: A piezoresistive electrogoniometer attached to the skin over the sacrum and a three-dimensional video analysis system with reflective markers on anatomical landmarks were both employed to measure the repositioning accuracy of pelvic tilting in standing. Eleven subjects without low back pain participated in this study. RESULTS: The overall mean repositioning accuracy was 1.87 degrees. Probability values from repeated measures ANOVA revealed no significant mean absolute error (AE) differences between sessions. Correlation coefficients between electrogoniometer and 3-D video analysis measurements of position sense ranged from 0.84 to 0.97. CONCLUSIONS: The proposed instruments and method are adequate for measuring lumbosacral repositioning accuracy. Healthy subjects are capable of repositioning their pelvis and back precisely. RELEVANCE: A reliable method assessing the lumbosacral repositioning accuracy can add insight into neuromuscular dysfunction as a cause of mechanical low back pain.

Effect of paraspinal muscle vibration on position sense of the lumbosacral spine.

STUDY DESIGN: A two-group experimental design with repeated measures on one factor was used. OBJECTIVES: To investigate the role of the muscle spindles of the paraspinal muscles in lumbosacral position sense of healthy individuals. SUMMARY OF BACKGROUND DATA: Muscle spindles are recognized to be important mediators for position and movement sense in peripheral joints, and they are very sensitive to mechanical vibration. However, little is known about their role in the control of lumbosacral spine positioning. METHODS: Twenty-five young individuals with no low back pain were assigned at random to an experimental or control group. Proprioceptive information of the multifidus muscle spindles was distorted in half of the trials in 16 individuals by manually applying vibration (70 Hz, 0.5 mm amplitude) for approximately 5 seconds. The control group (n = 9) only heard the vibrator noise during repositioning of the lumbosacral spine. Repositioning accuracy in the sitting position was estimated by calculating the mean absolute error, constant error, and variable error among six criteria and reproduction sacral tilt angles. RESULTS: Multifidus muscle vibration induced a significant muscle lengthening illusion through which the members of the experimental group undershot the target position (F(1,15) = 30.77, P < 0.0001). The position sense scores of the control group displayed no significant differences across trials (F(1,8) = 0.56, P > 0.05). CONCLUSIONS: The findings suggest that precise muscle spindle input of the paraspinal muscles is essential for accurate positioning of the pelvis and lumbosacral spine in a sitting posture.

Lumbosacral position sense during pelvic tilting in men and women without low back pain: test development and reliability assessment.

STUDY DESIGN: A single group test-retest design to evaluate the reproducibility of lumbosacral position sense measurements. OBJECTIVES: To develop a measure of position sense in the lumbosacral area and to determine test-retest reliability. BACKGROUND: Proprioception, muscle control, and coordination training could be the key issues in resolving neuromuscular dysfunction in patients with low back pain, but there are no standard ways to assess these parameters. METHODS AND MEASURES: A piezoresistive accelerometer attached to the skin over the sacrum was used to research the repositioning accuracy of active pelvic tilting, between days, of 14 young nonimpaired subjects (20 to 26 years of age) in standing. RESULTS: The mean absolute error for repositioning accuracy (the difference between criterion and matching positions) was 1.81 degrees (+/- 0.85). The intraclass correlation coefficient between measurements obtained on days 1 and 2 was moderate (R = 0.51). The average standard error of measurement associated with the intraclass correlation coefficient was 0.5 degree (95% confidence interval = +/- 0.99 degree). CONCLUSIONS: These findings suggest that the proposed test is sensitive with moderate test-retest reliability to examine lumbosacral position sense in healthy subjects. Further adjustments in the testing protocol are needed to improve the test-retest reliability.