Evaluation des propriétés mécaniques des muscles cervicaux (analyse du comportement dynamique du segment tête-cou lors de l'application de détentes rapides)

La stabilisation de la tête détermine l équilibre corporel, la prise d informations sensorielles et la protection des centres nerveux. Elle est régulée en partie par la raideur musculo-tendineuse des muscles cervicaux qui n a jamais été étudiée auparavant. Par ailleurs, la méthode de détentes rapides élaborée pour évaluer la raideur musculo-tendineuse n a jamais été appliquée à des segments corporels multi-articulaires. Les objectifs de ce travail sont de développer une méthode d évaluation de la raideur musculo-tendineuse du segment tête-cou par application de détentes rapides, de modéliser le segment tête-cou en un système mono-articulaire et d étudier les effets de la fatigue périphérique sur la raideur musculo-tendineuse du segment tête-cou. L analyse cinématique de la tête par accélérométrie montre que la relation entre le déplacement angulaire lors de détentes rapides et le niveau de force est reproductible. Les résultats n ont montré aucune relation entre la raideur musculo-tendineuse et le niveau de force. L analyse de la cinématique du segment tête-cou par un procédé d optimisation nous a permis de mettre en évidence une augmentation de la raideur musculo-tendineuse avec le niveau de force. D autre part, la fatigue périphérique ne semble pas générer de modifications de la raideur musculo-tendineuse des muscles cervicaux. Les résultats montrent que l application de détentes rapides, associée à une modélisation du segment tête-cou en un système mono-articulaire, semble aboutir à une estimation fiable de la raideur musculo-tendineuse du segment tête-couPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Kinematic analysis of the head by inertial sensors. Test-retest reproducibility and clinical use feasibility

The aim of this study was to evaluate the reproducibility of a protocol using inertial sensors in order to characterize primary and associated movements of the head. Twenty-two subjects were evaluated twice in the same experimental conditions (3 days interval). Two inertial sensors allowed the evaluation of the range of movement of the head. Three complete cycles of movements were realised in each plane. A patient suffering from cervical dystonia was also evaluated with the same protocol before and after self-training program. Results show a good reproducibility for all ranges of movement except for the associated movements realised in the sagittal plane. Thereafter, our protocol allowed us to notice an improvement of the kinematics of the head after the self-training program followed by the patient. These results show the reproducibility of the inertial sensors as evaluation tools for head movements, a change in the proposed method will allow a generalization to cervical movements

Repositioning errors of the head in straight-ahead position in cervical dystonia: Influence of clinical features and movement planes

International audienc

Force and EMG activity of cervical muscles.

<p>Typical normalized force according to MVC (F_MVC) (A) and EMG recording on right cervical extensor (SE_R), left cervical extensor (SE_L), right cervical flexor (SCM_R), and left cervical flexor (SCM_L) (respectively B, C, D, and E) for one subject. EMG parameters were recorded over the last 512 ms of the isometric contraction (colored area) before the release during QR trial (here, 30% MVC trial).</p

Subject placed in sitting.

<p>The headgear is positioned on the head and fixed with the cable to the wall-mounted system composed of the electromagnet and the load cell. Kinematics of the five LEDs positioned on the head (L 1, L2, L3, L 4, and L 5) were measured with respect to the LED 6 (L 6), placed on the shoulder.</p

Mean and SD values of EMG parameters of all muscles evaluated before and after the fatigue procedure (*P < 0.05).

<p>Mean and SD values of EMG parameters of all muscles evaluated before and after the fatigue procedure (*P < 0.05).</p

Configuration of head-neck segment rotation.

<p>M is a point of the head-neck rigid segment rotating around the resultant center of rotation (CoR) in <math><mrow><mo stretchy="false">(</mo>O<mo>,</mo>X<mo>→</mo><mo>,</mo>Y<mo>→</mo><mo>,</mo>Z<mo>→</mo><mo stretchy="false">)</mo></mrow></math>. Here, X_CoR and Y_CoR represent respectively horizontal and vertical CoR components, L_M is the radius of rotation of point M, θ₀ is the initial angular position of point M, relative to the horizontal axis (X), and θ(t) is the angular position of point M, function of time (t), and relative to θ₀. Anti-clockwise rotation is positive.</p

EMG parameters of cervical muscles.

<p>Evolution of RMS (top) and MDF (bottom) between before (No fatigue) and after (Fatigue) the fatigue procedure during the isometric contractions of QR (*P < 0.05).</p

Evolution of stiffness index with fatigue.

<p>The relationship between the head-neck segment musculo-tendinous stiffness (S) and the isometric cervical flexion torque developed before the QR (T) for all subjects before and after the fatigue procedure (No fatigue and Fatigue, respectively). Linear regression showed a significant and linear increase of S according to T in the two conditions (P < 0.0001). There was no significant difference for the slopes of the linear regressions, providing the stiffness index of the head-neck segment in flexion, between the two conditions.</p

Free-Living Physical Activity and Sedentary Behaviour in Autoimmune Myasthenia Gravis: A Cross-Sectional Study

International audienceBackground: Muscle weakness and fatigability, the prominent symptoms of autoimmune myasthenia gravis (MG), impact negatively on daily function and quality of life (QoL). It is currently unclear as to what extent symptoms limit activity and whether physical activity (PA) behaviours are associated with reduced QoL. Objectives: This study aimed to describe habitual PA patterns and explore relationships between PA metrics, clinical MG characteristics, and health-related QoL (HRQoL). Methods: PA data from a trunk tri-axial accelerometer worn for seven days, was collected from females with generalized, stable MG and compared to control subjects. MG-specific evaluations, the six-minute walk test and knee extension strength were assessed in individuals with MG (IwMG). Mann-Whitney tests were used to study between-group differences. Spearman rank correlation coefficient was performed to explore relationships between variables. Results: Thirty-three IwMG (mean (SD) age 45 (11) years) and 66 control subjects were included. IwMG perform less vigorous-intensity PA than control subjects (p = 0.001), spend more time sedentary (p = 0.02) and engage in less and shorter durations of moderate-vigorous-intensity PA (MVPA). For IwMG, habitual PA correlated positively with 6 min walking distance (rho = 0.387, p = 0.029) and negatively with body mass index (rho =-0.407, p = 0.019). We did not find any association between PA or sedentary behaviour and; HRQoL, symptom severity nor lower limb strength. Conclusions: Individuals with stable MG perform less PA, at lower intensities, and are more inactive than controls individuals. Further research is warranted to understand factors influencing PA patterns in MG and whether interventions could be successful in increasing PA quantity and intensity in IwMG