Location In Vivo of the Innervation Zone in the Human Medial Gastrocnemius Using Imposed Contractions: A Comparison of the Usefulness of the M-Wave and H-Reflex.

The anatomical territory where the neuromuscular junctions are grouped corresponds to the innervation zone (IZ). This can be located in-vivo using high-density electromyography and voluntary muscle contractions. However, in patients with motor impairment, the use of contractions imposed by electrical stimulation (ES) could be an alternative. The present study has two aims: Firstly, to describe the location of the IZ in-vivo of the medial gastrocnemius (MG) using imposed contractions by ES. Secondly, to compare the usefulness of M-waves and H-reflexes to localize the IZs. Twenty-four volunteers participated (age: 21.2 ± 1.5 years). ES was elicited in the tibial nerve to obtain M-waves and H-reflexes in the MG. The evaluators used these responses to localize the IZs relative to anatomical landmarks. M-wave and H-reflex IZ frequency identification were compared. The IZs of the MG were mostly located in the cephalocaudal direction, at 39.7% of the leg length and 34% of the knee's condylar width. The IZs were most frequently identified in the M-wave (83.33%, 22/24) compared to the H-reflex (8.33%, 2/24) (p > 0.001). Imposed contractions revealed that the IZ of the MG is located at 39.7% of the leg length. To locate the IZs of the MG muscle, the M-wave is more useful than the H-reflex.

Centro de presión y patrones de actividad muscular durante la ejecución de una sentadilla monopodal isométrica realizada sobre una superficie esponjosa en mujeres jóvenes sanas / Center of pressure and patterns of muscular activity during the execution of an isometric single leg squat performed on a spongy surface in healthy young women / Centro de pressão e padrões de atividade muscular durante a execução de um agachamento isométrico uni podal realizado em uma superfície esponjosa por mulheres jovens saudáveis

Objetivo: Comparar la ejecución del ejercicio de sentadilla monopodal isométrica, en una superficie rígida versus una superficie esponjosa, en relación al centro de presión y los patrones de activación de la musculatura de la extremidad inferior dominante y la columna, en mujeres jóvenes sanas. Método: 12 mujeres sanas, realizaron la sentadilla monopodal isométrica en una superficie rígida (control) y una superficie esponjosa. Un posturógrafo registró el área y velocidad de desplazamiento del centro de presión. Un electromiógrafo de superficie evaluó la actividad muscular de multífido, glúteo mayor, glúteo medio, vasto medial y bíceps femoral de la pierna de apoyo. Resultados: El área y la velocidad de desplazamiento del centro de presión aumentó (p<0.05 y p<0.01 respectivamente) en superficie esponjosa. El bíceps femoral aumenta su actividad muscular en superficie esponjosa (p<0.05). Existe correlación entre la mayor actividad muscular del bíceps femoral y el área y la velocidad del centro de presión (p<0.01). Conclusión: La sentadilla monopodal isométrica realizada sobre una superficie esponjosa, produce una mayor perturbación del control postural y una mayor actividad del bíceps femoral en mujeres jóvenes sanas. El aumento de actividad de este músculo se relaciona directamente con el desplazamiento del centro de presión

Objective: To compare the performance of the isometric single leg squat exercise on a rigid surface versus a spongy surface in relation to the center of pressure and activation patterns of the muscles of the dominant lower limb and spine in healthy young women. Method: 12 healthy women performed the isometric single leg squat on a rigid surface (control) and a spongy surface. A posturograph recorded the area and velocity of displacement of the pressure center. A surface electromyograph evaluated the muscular activity of multifidus, gluteus maximus, gluteus medius, vastus medialis and biceps femoris of the supporting leg. Results: The area and the speed of displacement of the center of pressure increased (p <0.05 and p <0.01 respectively) in spongy surface. Femoral biceps increase its muscular activity on the spongy surface (p <0.05). There is a correlation between the greater muscular activity of the biceps femoris and the area and the velocity of the pressure center (p <0.01). Conclusion: Isometric single leg squat performed on a spongy surface, produces a greater disturbance of postural control and greater activity of the biceps femoris in healthy young women. The increased activity of this muscle is directly related to the displacement of the pressure center

Objetivo: Comparar o desempenho no agachamento isométrico uni podal em superfície rígida versus superfície esponjosa em relação ao centro de pressão e padrões de ativação dos músculos do membro inferior dominante e coluna vertebral em mulheres jovens saudáveis. Método: 12 mulheres saudáveis realizaram o agachamento isométrico uni podal em uma superfície rígida (controle) e uma superfície esponjosa. Um posturógrafo registrou a área e a velocidade de deslocamento do centro de pressão. Um eletromiógrafo de superfície avaliou a atividade muscular de multifidus, glúteo máximo, glúteo médio, vasto medial e bíceps femoral da perna de apoio. Resultados: A área e a velocidade de deslocamento do centro de pressão aumentaram (p <0.05 e p <0.01, respectivamente) na superfície esponjosa. O bíceps femoral aumenta sua atividade muscular na superfície esponjosa (p <0.05). Existe uma correlação entre a maior atividade muscular do bíceps femoral e a área e a velocidade do centro de pressão (p <0.01). Conclusão: Agachamento isométrico uni podal realizado em uma superfície esponjosa, produz uma maior perturbação do controle postural e uma maior atividade do bíceps femoral em mulheres jovens saudáveis. O aumento da atividade desse músculo está diretamente relacionado ao deslocamento do centro de pressão

Spectral components in electromyograms from four regions of the human masseter, in natural dentate and edentulous subjects with removable prostheses and implants.

OBJECTIVE: To compare the frequency or spectral components between different regions of the superficial masseter in young natural dentate and total edentulous older adults rehabilitated with removable prostheses and fixed-implant support. A secondary objective was to compare these components between the three groups. DESIGN: 21 young natural dentate and 28 edentulous (14 with removable prostheses and 14 with fixed-implant support) were assessed. High-density surface electromyography (sEMG) was recorded in four portions of the superficial masseter during submaximal isometric bites. Spectral components were obtained through a spectral analysis of the sEMG signals. An analysis of mixed models was used to compare the spectral components. RESULTS: In all groups, the spectral components of the anterior portion were lower than in the posterior region (p < 0.05). Both edentulous groups showed lower spectral components and median frequency slope than the natural dentate group (p < 0.05). The removable prostheses group showed the greatest differences with natural dentate group. CONCLUSIONS: There were significant differences in the spectral components recorded in the different regions of the superficial masseter. The lower spectral components and fatigability of older adults rehabilitated with prostheses could be a cause of a greater loss of type II fibers, especially in the removable prostheses group.

Functional compartmentalization of the human superficial masseter muscle.

Some muscles have demonstrated a differential recruitment of their motor units in relation to their location and the nature of the motor task performed; this involves functional compartmentalization. There is little evidence that demonstrates the presence of a compartmentalization of the superficial masseter muscle during biting. The aim of this study was to describe the topographic distribution of the activity of the superficial masseter (SM) muscle's motor units using high-density surface electromyography (EMGs) at different bite force levels. Twenty healthy natural dentate participants (men: 4; women: 16; age 20±2 years; mass: 60±12 kg, height: 163±7 cm) were selected from 316 volunteers and included in this study. Using a gnathodynamometer, bites from 20 to 100% maximum voluntary bite force (MVBF) were randomly requested. Using a two-dimensional grid (four columns, six electrodes) located on the dominant SM, EMGs in the anterior, middle-anterior, middle-posterior and posterior portions were simultaneously recorded. In bite ranges from 20 to 60% MVBF, the EMG activity was higher in the anterior than in the posterior portion (p-value = 0.001).The center of mass of the EMG activity was displaced towards the posterior part when bite force increased (p-value = 0.001). The topographic distribution of EMGs was more homogeneous at high levels of MVBF (p-value = 0.001). The results of this study show that the superficial masseter is organized into three functional compartments: an anterior, a middle and a posterior compartment. However, this compartmentalization is only seen at low levels of bite force (20-60% MVBF).

Differences between motor point and innervation zone locations in the biceps brachii. An exploratory consideration for the treatment of spasticity with botulinum toxin.

BACKGROUND: Botulinum toxin (BTX) acts on the neuromuscular junction which can be located by the innervation zone (IZ). Clinically, the motor point (MP) is homologous to the IZ and it is used as the injection site of BTX. Differences in the effectiveness of the application of BTX between MP and IZ locations have been determined. OBJECTIVE: Compare the location of the MP obtained using electrical stimulation and the location of the IZ using a linear surface electrodes array on the biceps brachii muscle. METHODS: The biceps brachii muscle of twenty men was assessed. The MP was located using the torque measurement generated by electrical stimulation. The IZ was detected using a linear surface electrodes array. RESULTS: A difference between the MP and the IZ positions (75.8 vs. 86.5mm, delta 10.7 mm; p=0.003, post-hoc power 0.89) was observed. DISCUSSION: The magnitude of the difference between the MP and the IZ may be clinically relevant. The IZ location using surface electromyography as a guide to optimize BTX injection is proposed.