Alain Hamaoui

Postural sway increase in low back pain subjects is not related to reduced spine range of motion

This study questioned whether postural sway increase in low back pain subjects was related to impaired spine mobility, and especially to a decrease in the range of motion, which was assumed to represent structural spine stiffness. Ten low back pain subjects and ten healthy control subjects performed spine flexion-extension and spine side bending tests, and standing posturographic examination in different experimental conditions. Low back pain subjects showed increased postural sway along the antero-posterior axis and reduced side bending, i.e. posturographic and range of motion parameters varied in the opposite direction. Moreover, no correlation was found between these two types of parameters. Although significant, the slight decrease in spine side bending did not seem sufficiently great to disturb the low amplitude movements that maintain postural equilibrium. Hence, it was concluded that postural sway increase in low back pain is not related to a reduced spine range of motion, but might be linked to an increase in muscular active tension, which reduces dynamic mobility capacity.

Does respiration perturb body balance more in chronic low back pain subjects than in healthy subjects

OBJECTIVE To determine whether body balance is perturbed more in low back pain patients than in healthy subjects, under the concept of posturo-kinetic capacity. DESIGN Comparison of posturographic and respiratory parameters between low back pain and healthy subjects. BACKGROUND It has been demonstrated that respiratory movements constitute a perturbation to posture, compensated by movements of the spine and of the hips, and that low back pain is frequently associated with a loss of back mobility. METHOD Ten low back pain patients and ten healthy subjects performed five posturographic tests under three different respiratory rate conditions: quiet breathing (spontaneous), slow breathing (0.1 Hz) and fast breathing (0.5 Hz). RESULTS Intergroup comparison showed that the mean displacements of the center of pressure were greater for the low back pain group, especially along the antero-posterior axis, where respiratory perturbation is primarily exerted. Inter-condition comparison showed that in slow and fast breathing relatively to quiet breathing, the mean displacement of the center of pressure along the antero-posterior axis was significantly increased only for the low back pain group. CONCLUSION According to the results, respiration presented a greater disturbing effect on body balance in low back pain subjects. RELEVANCE This study provides information on the causes of the impaired body balance associated with chronic low back pain, which could be used to improve treatment strategy.

Respiratory disturbance to posture varies according to the respiratory mode.

The purpose of this study was to determine whether respiratory disturbance to posture varies as a function of the respiratory mode, i.e. thoracic or abdominal. To this aim, 10 healthy male subjects underwent a posturographic examination associated with a measurement of respiratory kinematics. Experimental conditions varied posture (sitting, standing) respiratory amplitude (quiet breathing, deep breathing) and respiratory mode (thoracic, abdominal). In addition to classical posturographic parameters, original peak detection algorithm and emergence parameter calculated from the Fast Fourier Transform were used to assess the respiratory component in CP displacements. Results showed that along the antero-posterior axis, time domain and frequency domain parameters were both significantly greater in thoracic breathing mode than in abdominal mode. It was concluded that respiratory kinematics have a more prominent disturbing effect on posture when they involve the rib cage rather than the abdomen.

Does increased muscular tension along the torso impair postural equilibrium in a standing posture

This paper focused on the relationship between active muscular tension along the torso and postural equilibrium while standing. Eleven healthy male subjects underwent a posturographic examination associated with a bimanual compression of a dynamometric bar, which was used to set the torso muscular activity at three different levels (0MVC, 20MVC, 40MVC). Electromyographic pre-tests identified the main superficial muscles of the compressive load as: pectoralis major, latissimus dorsi, thoracic and lumbar erector spinae. Kinematics of the chest wall was recorded by means of two sensing belts, in order to assess the respiratory component of the center of pressure (CP) signal. The analysis of time-domain stabilometric parameters showed that CP displacements were larger and faster in 40MVC that in 20MVC, with no variation between 0MVC and 20MVC. The respiratory component of the CP signal was not sensitive to the compressive load. It was concluded that increased muscular tension along the torso is likely to disturb postural equilibrium, but only when it exceeds a given level.

Effect of seat and table top slope on the biomechanical stress sustained by the musculo-skeletal system

The purpose of this study was to assess the effect of table and seat slope on the biomechanical stress sustained by the musculo-skeletal system. Angular position of the head and trunk, and surface electromyography of eleven postural muscles were recorded while seated under different conditions of seat slope (0°, 15° forward) and table slope (0°, 20° backward). The specific stress sustained by C7-T1 joint was estimated with isometric torque calculation. The results showed that the backward sloping table was associated with a reduction of neck flexion and neck extensors EMG, contrasting with a concurrent overactivity of the deltoideus. The forward sloping chair induced an anterior pelvic tilt, but also a higher activity of the knee (vasti) and ankle (soleus) extensors. It was concluded that sloping chairs and tables favor a more erect posture of the spine, but entails an undesirable overactivity of upper and lower limbs muscles to prevent the body from sliding.

Sitting on a Sloping Seat Does Not Reduce the Strain Sustained by the Postural Chain

The objective of this study was to explore the effect of a forward sloping seat on posture and muscular activity of the trunk and lower limbs. To this aim, twelve asymptomatic participants were tested in six conditions varying seat slope (0°, 15° forward) and height (high, medium, low). Angular position of head, trunk and pelvis was assessed with an inertial orientation system, and muscular activity of 11 superficial postural muscles located in the trunk and lower limbs was estimated using normalized EMG. Results showed that a forward sloping seat, compared to a flat seat, induced a greater activity of the soleus (p<0.01), vastus lateralis (p<0.05) and vastus medialis (p<0.05), as well a lower hip flexion (p<0.01). In contrast, no significant variation of head, trunk and pelvis angular position was observed according to seat slope. It was concluded that forward sloping seats increase the load sustained by the lower limbs, without a systematic improvement of body posture.

Does increased muscular tension along the torso disturb postural equilibrium more when it is asymmetrical

The aim of this study was to determine whether increased muscular tension disturbs postural equilibrium more when it is asymmetrical. Ten healthy male subjects underwent a posturographic examination associated with an original uni and bilateral compressive load paradigm designed to set the active muscular tension at different controlled levels along each side of the torso. Respiratory kinematics were recorded by means of two sensing belts. Two electromyographic pre-tests were used to map out the main motor muscles of the task and to quantify the level of asymmetry induced by unilateral loads. The posturographic examination revealed that the mean deviation of the CP along the medial-lateral axis was significantly greater in unilateral than in bilateral compressive loads. It was suggested that increased muscular tension along the torso induces a more disturbing effect on posture when it is asymmetrical.

Influence of Cervical Spine Mobility on the Focal and Postural Components of the Sit-to-Stand Task

The aim of this study was to determine the influence of cervical spine mobility on the focal and postural components of the sit-to-stand transition, which represent the preparatory and execution phases of the task, respectively. Sixteen asymptomatic female participants (22 ± 3 years, 163 ± 0,06 cm, 57,5 ± 5 kg), free of any neurological or musculoskeletal disorders, performed six trials of the sit-to-stand task at maximum speed, in four experimental conditions varying the mobility of the cervical spine by means of three different splints. A six-channel force plate, which collected the reaction forces and moments applied at its top surface, was used to calculate the center of pressure displacements along the anterior-posterior and medial-lateral axes. The local accelerations of the head, spine, and pelvis, were assessed by three pairs of accelerometers, oriented along the vertical and anterior-posterior axes. Restriction of cervical spine mobility resulted in an increased duration of the focal movement, associated with longer and larger postural adjustments. These results suggest that restricted cervical spine mobility impairs the posturo-kinetic capacity during the sit-to-stand task, leading to a lower motor performance and a reorganization of the anticipatory postural adjustments. In a clinical context, it might be assumed that preserving the articular free play of the cervical spine might be useful to favor STS performance and autonomy.

Effect of experimentally-induced trunk muscular tensions on the sit-to-stand task performance and associated postural adjustments

It has been shown that increased muscular activity along the trunk is likely to impair body balance, but there is little knowledge about its consequences on more dynamic tasks. The purpose of this study was to determine the effect of unilateral and bilateral increases of muscular tension along the trunk on the sit-to-stand task (STS) performance and associated anticipatory postural adjustments (APAs). Twelve healthy females (23 ± 3 years, 163 ± 0.06 cm, 56 ± 9 kg), free of any neurological or musculoskeletal disorders, performed six trials of the STS at maximum speed, in seven experimental conditions varying the muscular tension along each side of the trunk, using a specific bimanual compressive load paradigm. A six-channel force plate was used to calculate the coordinates of the center of pressure (CP) along the anterior-posterior and medial-lateral axes, and the kinematics of the head, spine and pelvis, were estimated using three pairs of uni-axial accelerometers. The postural and focal components of the task were assessed using three biomechanical parameters calculated from CP signals: the duration and magnitude of APAs, and the duration of focal movement (dFM). Results showed that beyond a given level, higher muscular tension along the trunk results in longer APAs, but with a stable duration of the focal movement. In addition, no significant variation of APAs and FM parameters was found between bilateral and unilateral increases of muscular tension. It was suggested that restricted mobility due to higher muscular tension along the trunk requires an adaptation of the programming of APAs to keep the same level of performance in the STS task. These findings may have implications in treatment strategies aimed at preserving functional autonomy in pathologies including a rise of muscular tension.

Short-Term Effects of Thoracic Spine Manipulation on the Biomechanical Organisation of Gait Initiation: A Randomized Pilot Study

Speed performance during gait initiation is known to be dependent on the capacity of the central nervous system to generate efficient anticipatory postural adjustments (APA). According to the posturo-kinetic capacity (PKC) concept, any factor enhancing postural chain mobility and especially spine mobility, may facilitate the development of APA and thus speed performance. “Spinal Manipulative Therapy High-Velocity, Low-Amplitude” (SMT-HVLA) is a healing technique applied to the spine which is routinely used by healthcare practitioners to improve spine mobility. As such, it may have a positive effect on the PKC and therefore facilitate gait initiation. The present study aimed to investigate the short-term effect of thoracic SMT-HVLA on spine mobility, APA and speed performance during gait initiation. Healthy young adults (n = 22) performed a series of gait initiation trials on a force plate before (“pre-manipulation” condition) and after (“post-manipulation” condition) a sham manipulation or an HVLA manipulation applied to the ninth thoracic vertebrae (T9). Participants were randomly assigned to the sham (n = 11) or the HVLA group (n = 11).The spine range of motion (ROM) was assessed in each participant immediately after the sham or HVLA manipulations using inclinometers. The results showed that the maximal thoracic flexion increased in the HVLA group after the manipulation, which was not the case in the sham group. In the HVLA group, results further showed that each of the following gait initiation variables reached a significantly lower mean value in the post-manipulation condition as compared to the pre-manipulation condition: APA duration, peak of anticipatory backward center of pressure displacement, center of gravity velocity at foot-off, mechanical efficiency of APA, peak of center of gravity velocity and step length. In contrast, for the sham group, results showed that none of the gait initiation variables significantly differed between the pre- and post-manipulation conditions. It is concluded that HVLA manipulation applied to T9 has an immediate beneficial effect on spine mobility but a detrimental effect on APA development and speed performance during gait initiation. We suggest that a neural effect induced by SMT-HVLA, possibly mediated by a transient alteration in the early sensory-motor integration, might have masked the potential mechanical benefits associated with increased spine mobility.