Changes in muscle coactivation during running: a comparison between two techniques, forefoot vs rearfoot / Cambios en la coactivación muscular durante la carrera: una comparación entre dos técnicas (antepié vs retropié)

Introduction: Surface electromyography has been a technique used to describe muscle activity during running. However, there is little literature that analyses the behaviour of muscle coactivation in runners, describing the effect between two techniques associated with the initial contact, such as the use of rearfoot (RF) and forefoot (FF). Material and method: The purpose of this study was to compare muscle coactivation levels developed in the lower limb during two running techniques, FF vs RF. Fourteen amateur runners were evaluated (eight men, six women; age= 23.21 ± 3.58 years, mass= 63.89 ± 8.13 kg, height= 1.68 ± 0.08m). Surface electromyography was used to measure muscle activity during both running techniques evaluated on a treadmill, considering the muscle pairs: Rectus femoris- Biceps femoris (RFe-BF), Lateral Gastrocnemius–Tibialis Anterior (LG-TA), and Medial Gastrocnemius - Tibialis Anterior (MG-TA). These were calculated in three windows considering ten running cycles (0-5%, 80-100%, and 0-100%). To compare FF vs RF t-student test for paired data was used. Results: It was observed significant differences in the MG-TA pair (FF= 18.42 ± 11.84% vs RF = 39.05 ± 13.28%, p = 0.0018 during 0-5%, and RFe-BF pair (FF = 42.38 ± 18.11% vs RF = 28.37 ± 17.2%, p = 0.0331) during 80-100% of the race. Conclusion: Our findings show that the behaviour of muscle coactivation is different between FF vs RF techniques if we analyze little windows in the running cycle. This could be associated with an increase in the joint stability between these short intervals, represented in the initial and final regions of the running cycle.(AU)

Introducción: La electromiografía de superficie ha sido una técnica usada para describir la actividad muscular durante la carrera. Sin embargo, hay poca literatura que analice el comportamiento de la coactivación muscular en corredores, descri­biendo el efecto entre dos técnicas asociadas al contacto inial, tal como el uso de retropié y antepié. Material y método: El propósito de este estudio fue comparar los niveles de coactivación desarrollados en la extremidad inferior, utilizando dos técnicas de carrera, antepié (FF) vs retropié (RF). Catorce corredores amateurs fueron evaluados (8 hombres, 6 mujeres; edad = 23,21 ± 3,58 años, masa = 63,89± 8,13 kg, estatura = 1,68 ± 0,08 m). Se utilizó electromiografía de superficie para medir la actividad muscular al momento de ejecutar ambas técnicas de carrera sobre una trotadora, conside­rando los siguientes pares musculares: Recto Femoral- Bíceps Femoral (RFe-BF), Gastrocnemio Lateral – Tibial Anterior (LG-TA) y Gastrocnemio Medial - Tibial Anterior (MG-TA). Estos se calcularon en tres ventanas considerando diez ciclos de ejecución (0-5%, 80-100% y 0-100%). Para comparar FF vs RF se utilizó la prueba t-student para datos pareados. Resultados: Se observan diferencias significativas en el par MG-TA (FF = 18,42 ± 11,84% vs RF = 39,05 ± 13,28%, p = 0,0018) durante el 0-5%, y el par RFe-BF (FF = 42,38 ± 18,11% vs RF = 28,37 ± 17,2%, p = 0,0331) durante el 80-100% de la carrera. Conclusión: Nuestros hallazgos muestran que el comportamiento de la coactivación muscular es diferente entre las técnicas de FF y RF si analizamos pequeñas ventanas en el ciclo de carrera. Esto podría estar asociado con un aumento de la estabilidad articular entre estos cortos intervalos, representados en la región inicial y final del ciclo de carrera.(AU)

Role of the CaMKII/NMDA receptor complex in the maintenance of synaptic strength.

During long-term potentiation (LTP), synapses undergo stable changes in synaptic strength. The molecular memory processes that maintain strength have not been identified. One hypothesis is that the complex formed by the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and the NMDA-type glutamate receptor (NMDAR) is a molecular memory at the synapse. To establish a molecule as a molecular memory, it must be shown that interfering with the molecule produces a persistent reversal of LTP. We used the CN class of peptides that inhibit CaMKII binding to the NR2B subunit in vitro to test this prediction in rat hippocampal slices. We found that CN peptides can reverse saturated LTP, allowing additional LTP to be induced. The peptide also produced a persistent reduction in basal transmission. We then tested whether CN compounds actually affect CaMKII binding in living cells. Application of CN peptide to slice cultures reduced the amount of CaMKII concentrated in spines, consistent with delocalization of the kinase from a binding partner in the spine. To more specifically assay the binding of CaMKII to the NMDAR, we used coimmunoprecipitation methods. We found that CN peptide decreased synaptic strength only at concentrations necessary to disrupt the CaMKII/NMDAR complex, but not at lower concentrations sufficient to inhibit CaMKII activity. Importantly, both the reduction of the complex and the reduction of synaptic strength persisted after removal of the inhibitor. These results support the hypothesis that the CaMKII/NMDAR complex has switch-like properties that are important in the maintenance of synaptic strength.