Lotte Janssens

Altered postural control in anticipation of postural instability in persons with recurrent low back pain

Insight into the mechanisms of altered postural control in persons with low back pain (LBP) could lead to better interventions for patients with LBP. This study investigated (1) whether persons with recurrent LBP have an altered body inclination, and (2) whether anticipation of postural instability further alters body inclination. Thirty-three young healthy individuals and 56 young persons with recurrent LBP participated in this study. The upright standing posture was evaluated by means of two piezo-resistive electrogoniometers and a force platform for the conditions as follows: (1) quiet stance with and without vision, and (2) in anticipation of postural instability due to a ballistic arm movement or ankle muscle vibration. No differences in body inclination were observed when visual information was available between the two groups (P>0.05). However, significant more forward inclination was seen in the persons with recurrent LBP when vision was occluded (+7.4%) and in anticipation of postural instability (+19%) (P<0.05) compared to the healthy individuals. The results suggest that young persons with recurrent LBP have an altered body inclination that might be caused by anticipation of postural instability. The adopted forward inclined posture may potentially be a factor in the recurrence of LBP.

The Effect of Inspiratory Muscles Fatigue on Postural Control in People With and Without Recurrent Low Back Pain

Study Design. A 2-group experimental design. Objective. To determine postural stability and proprioceptive postural control strategies of healthy subjects and subjects with recurrent low back pain (LBP) during acute inspiratory muscles fatigue (IMF). Summary of Background Data. People with LBP use a more rigid proprioceptive postural control strategy than control subjects during postural perturbations. Recent evidence suggests that respiratory movements create postural instability in people with LBP. The role of the respiratory muscles in postural control strategies is unknown, but can be studied by inducing acute IMF. Methods. Postural control was evaluated in 16 people with LBP and 12 healthy controls, both before and after IMF. Center of pressure displacement was determined on a force plate to evaluate postural stability. Proprioceptive postural control strategies were examined during vibration of the triceps surae muscles or lumbar paraspinal muscles, while standing on both a stable and unstable support surface and without vision. Proprioceptive postural control strategies were determined by examining the ratio of mean center of pressure displacement measured during triceps surae muscles vibration to that measured during lumbar paraspinal muscles vibration. Results. After IMF, control subjects showed a significantly larger sway compared to the unfatigued condition while standing on an unstable support surface (P < 0.05). IMF induced an increased reliance on proprioceptive signals from the ankles, which resembled the postural control strategy used by people with LBP (P < 0.05). Subjects with LBP showed that same ankle steered postural control strategy in the unfatigued and IMF states (P > 0.05). Conclusion. After IMF, control subjects use a rigid proprioceptive postural control strategy, rather than the normal “multisegmental” control, which is similar to people with LBP. This results in decreased postural stability. These results suggest that IMF might be a factor in the high recurrence rate of LBP.

A Clinical Measurement to Quantify Spasticity in Children with Cerebral Palsy by Integration of Multidimensional Signals

Most clinical tools for measuring spasticity, such as the Modified Ashworth Scale (MAS) and the Modified Tardieu Scale (MTS), are not sufficiently accurate or reliable. This study investigated the clinimetric properties of an instrumented spasticity assessment. Twenty-eight children with spastic cerebral palsy (CP) and 10 typically developing (TD) children were included. Six of the children with CP were retested to evaluate reliability. To quantify spasticity in the gastrocnemius (GAS) and medial hamstrings (MEH), three synchronized signals were collected and integrated: surface electromyography (sEMG); joint-angle characteristics; and torque. Muscles were manually stretched at low velocity (LV) and high velocity (HV). Spasticity parameters were extracted from the change in sEMG and in torque between LV and HV. Reliability was determined with intraclass-correlation coefficients and the standard error of measurement; validity by assessing group differences and correlating spasticity parameters with the MAS and MTS. Reliability was moderately high for both muscles. Spasticity parameters in both muscles were higher in children with CP than in TD children, showed moderate correlation with the MAS for both muscles and good correlation to the MTS for the MEH. Spasticity assessment based on multidimensional signals therefore provides reliable and clinically relevant measures of spasticity. Moreover, the moderate correlations of the MAS and MTS with the objective parameters further stress the added value of the instrumented measurements to detect and investigate spasticity, especially for the GAS.

Proprioceptive changes impair balance control in individuals with chronic obstructive pulmonary disease.

Introduction Balance deficits are identified as important risk factors for falling in individuals with chronic obstructive pulmonary disease (COPD). However, the specific use of proprioception, which is of primary importance during balance control, has not been studied in individuals with COPD. The objective was to determine the specific proprioceptive control strategy during postural balance in individuals with COPD and healthy controls, and to assess whether this was related to inspiratory muscle weakness. Methods Center of pressure displacement was determined in 20 individuals with COPD and 20 age/gender-matched controls during upright stance on an unstable support surface without vision. Ankle and back muscle vibration were applied to evaluate the relative contribution of different proprioceptive signals used in postural control. Results Individuals with COPD showed an increased anterior-posterior body sway during upright stance (p = 0.037). Compared to controls, individuals with COPD showed an increased posterior body sway during ankle muscle vibration (p = 0.047), decreased anterior body sway during back muscle vibration (p = 0.025), and increased posterior body sway during simultaneous ankle-muscle vibration (p = 0.002). Individuals with COPD with the weakest inspiratory muscles showed the greatest reliance on ankle muscle input when compared to the stronger individuals with COPD (p = 0.037). Conclusions Individuals with COPD, especially those with inspiratory muscle weakness, increased their reliance on ankle muscle proprioceptive signals and decreased their reliance on back muscle proprioceptive signals during balance control, resulting in a decreased postural stability compared to healthy controls. These proprioceptive changes may be due to an impaired postural contribution of the inspiratory muscles to trunk stability. Further research is required to determine whether interventions such as proprioceptive training and inspiratory muscle training improve postural balance and reduce the fall risk in individuals with COPD.

Microstructural Integrity of the Superior Cerebellar Peduncle Is Associated with an Impaired Proprioceptive Weighting Capacity in Individuals with Non-Specific Low Back Pain

Introduction Postural control is a complex sensorimotor task that requires an intact network of white matter connections. The ability to weight proprioceptive signals is crucial for postural control. However, research into central processing of proprioceptive signals for postural control is lacking. This is specifically of interest in individuals with non-specific low back pain (NSLBP), because impairments in postural control have been observed as possible underlying mechanisms of NSLBP. Therefore, the objective was to investigate potential differences in sensorimotor white matter microstructure between individuals with NSLBP and healthy controls, and to determine whether the alterations in individuals with NSLBP are associated with the capacity to weight proprioceptive signals for postural control. Methods The contribution of proprioceptive signals from the ankle and back muscles to postural control was evaluated by local muscle vibration in 18 individuals with NSLBP and 18 healthy controls. Center of pressure displacement in response to muscle vibration was determined during upright standing on a stable and unstable support surface. Diffusion magnetic resonance imaging was applied to examine whether this proprioceptive contribution was associated with sensorimotor white matter microstructure. Results Individuals with NSLBP showed a trend towards a reduced fractional anisotropy along the left superior cerebellar peduncle compared to healthy controls (p = 0.039). The impaired microstructural integrity of the superior cerebellar peduncle in individuals with NSLBP was significantly correlated with the response to ankle muscle vibration (p<0.003). Conclusions In individuals with NSLBP, a decreased integrity of the superior cerebellar peduncle was associated with an increased reliance on ankle muscle proprioception, even on unstable support surface, which implies an impaired proprioceptive weighting capacity. Our findings emphasize the importance of the superior cerebellar peduncle in proprioceptive weighting for postural control in individuals with NSLBP.

The assessment of inspiratory muscle fatigue in healthy individuals: A systematic review

Inspiratory muscle fatigue (IMF) may contribute to the development of exercise limitation and respiratory failure. Identifying fatigue of the inspiratory muscles requires a rigorous and integrative methodological approach. However, there is no consensus about an optimal protocol to induce and assess the fatigability of the inspiratory muscles. A systematic review was performed to identify, evaluate, and summarize the literature related to the assessment of induced IMF in healthy individuals. The aim was to identify factors that are related consistently to IMF, as well as to suggest possible assessment methods. MEDLINE and EMBASE were searched for relevant articles until February 2012. Only studies with a quantitative description of assessment and outcome were included. The search yielded 460 citations and a total of 77 studies were included. Inspiratory muscle fatigue was produced acutely by inspiratory resistive loading (IRL), whole body exercise (WBE), hyperpnea, or WBE combined with IRL, and under normocapnic, hypoxic or hypercapnic conditions. To detect IMF, most studies (64%) used phrenic nerve stimulation, 44% used a maximal voluntary inspiratory maneuver and the remainder used electromyography. The heterogeneity of the published reports precluded a quantitative analysis. Inspiratory resistive loadings at intensities of 60-80% of maximum, and cycling at 85% of maximum were found to produce IMF most consistently. Hypoxic or hypercapnic conditions, and WBE combined with IRL, exacerbated IMF. The specific outcome measures employed to detect IMF, the magnitude of their change, as well as their functional significance, are ultimately dependent upon the research question being addressed.

Impaired Postural Control Reduces Sit-to-Stand-to-Sit Performance in Individuals with Chronic Obstructive Pulmonary Disease

Background Functional activities, such as the sit-to-stand-to-sit (STSTS) task, are often impaired in individuals with chronic obstructive pulmonary disease (COPD). The STSTS task places a high demand on the postural control system, which has been shown to be impaired in individuals with COPD. It remains unknown whether postural control deficits contribute to the decreased STSTS performance in individuals with COPD. Methods Center of pressure displacement was determined in 18 individuals with COPD and 18 age/gender-matched controls during five consecutive STSTS movements with vision occluded. The total duration, as well as the duration of each sit, sit-to-stand, stand and stand-to-sit phase was recorded. Results Individuals with COPD needed significantly more time to perform five consecutive STSTS movements compared to healthy controls (19±6 vs. 13±4 seconds, respectively; p = 0.001). The COPD group exhibited a significantly longer stand phase (p = 0.028) and stand-to-sit phase (p = 0.001) compared to the control group. In contrast, the duration of the sit phase (p = 0.766) and sit-to-stand phase (p = 0.999) was not different between groups. Conclusions Compared to healthy individuals, individuals with COPD needed significantly more time to complete those phases of the STSTS task that require the greatest postural control. These findings support the proposition that suboptimal postural control is an important contributor to the decreased STSTS performance in individuals with COPD.

Resting-State Functional Connectivity of the Sensorimotor Network in Individuals with Nonspecific Low Back Pain and the Association with the Sit-to-Stand-to-Sit Task.

Individuals with nonspecific low back pain (NSLBP) show a decreased sit-to-stand-to-sit (STSTS) performance. This dynamic sensorimotor task requires integration of sensory and motor information in the brain. Therefore, a better understanding of the underlying central mechanisms of impaired sensorimotor performance and the presence of NSLBP is needed. The aims of this study were to characterize differences in sensorimotor functional connectivity in individuals with NSLBP and to investigate whether the patterns of sensorimotor functional connectivity underlie the impaired STSTS performance. Seventeen individuals with NSLBP and 17 healthy controls were instructed to perform five consecutive STSTS movements as fast as possible. Based on the center of pressure displacement, the total duration of the STSTS task was determined. In addition, resting-state functional connectivity images were acquired and analyzed on a multivariate level using both functional connectivity density mapping and independent component analysis. Individuals with NSLBP needed significantly more time to perform the STSTS task compared to healthy controls. In addition, decreased resting-state functional connectivity of brain areas related to the integration of sensory and/or motor information was shown in the individuals with NSLBP. Moreover, the decreased functional connectivity at rest of the left precentral gyrus and lobule IV and V of the left cerebellum was associated with a longer duration of the STSTS task in both individuals with NSLBP and healthy controls. In summary, individuals with NSLBP showed a reorganization of the sensorimotor network at rest, and the functional connectivity of specific sensorimotor areas was associated with the performance of a dynamic sensorimotor task.

Greater diaphragm fatigability in individuals with recurrent low back pain

The diaphragm plays an important role in spinal control. Increased respiratory demand compromises spinal control, especially in individuals with low back pain (LBP). The objective was to determine whether individuals with LBP exhibit greater diaphragm fatigability compared to healthy controls. Transdiaphragmatic twitch pressures (TwPdi) were recorded in 10 LBP patients and 10 controls, before and 20 and 45 min after inspiratory muscle loading (IML). Individuals with LBP showed a significantly decreased potentiated TwPdi, 20 min (-20%) (p=0.002) and 45 min (-17%) (p=0.006) after IML. No significant decline was observed in healthy individuals, 20 min (-9%) (p=0.662) and 45 min (-5%) (p=0.972) after IML. Diaphragm fatigue (TwPdi fall ≥ 10%) was present in 80% (20 min after IML) and 70% (45 min after IML) of the LBP patients compared to 40% (p=0.010) and 30% (p=0.005) of the controls, respectively. Individuals with LBP exhibit propensity for diaphragm fatigue, which was not observed in controls. An association with reduced spinal control warrants further study.

Altered preparatory pelvic control during the sit-to-stance-to-sit movement in people with non-specific low back pain

People with non-specific low back pain (LBP) show hampered performance of dynamic tasks such as sit-to-stance-to-sit movement. However, the underlying mechanisms remain obscure. Therefore, the aim of this study was to assess if proprioceptive impairments influence the performance of the sit-to-stance-to-sit movement. First, the proprioceptive steering of 20 healthy subjects and 106 persons with mild LBP was identified during standing using muscle vibration. Second, five sit-to-stance-to-sit repetitions on a stable support and on foam were performed as fast as possible. Total duration, phase duration, center of pressure (COP) displacement, pelvic and thoracic kinematics were analyzed. People with LBP used less lumbar proprioceptive afference for postural control compared to healthy people (P < 0.0001) and needed more time to perform the five repetitions in both postural conditions (P < 0.05). These time differences were determined in the stance and sit phases (transition phases), but not in the focal movement phases. Moreover, later onsets of anterior pelvic rotation initiation were recorded to start both movement sequences (P < 0.05) and to move from sit-to-stance on foam (P < 0.05). Decreased use of lumbar proprioceptive afference in people with LBP seemed to have a negative influence on the sit-to-stance-to-sit performance and more specifically on the transition phases which demand more control (i.e. sit and stance). Furthermore, slower onsets to initiate the pelvis rotation to move from sit-to-stance illustrate a decrease in pelvic preparatory movement in the LBP group.