Differences in Utilization of Lower Limb Muscle Power in Squat Jump With Positive and Negative Load.

Jump performance is related to the ability of lower limb muscles to produce power during the push-off phase. However, it is not known if the power associated with the action of active and passive elements of the lower limb muscles change significantly in jumps with positive and negative loads. In this study, the power associated with the action of passive and active components of lower limb muscles as a whole in squat jumps (SJ) with increase and decrease in the external load is analyzed Fourteen trained male subjects (22.5 ± 2.1 years; 176.5 ± 5.4 cm; 75.8 ± 5.8 kg; BMI 24.3 ± 1.8) performed SJ on a force plate. A functional electromechanical dynamometer (FEMD) system was used to change the external load in a range of -30 to +30% of the subject's body weight. A model comprising a mass, a spring, an active element, and a damper was used. We applied an optimization principle to determine power in center of mass (CoM) (ptot), the powers associated with active element (pact), damper (pƔ), and spring (pk) during the push-off phase. Significant differences between loading conditions for each variable were tested by repeated-measures one-way ANOVA with Bonferroni post hoc analysis, p < 0.05. Shapes of the average curves for instantaneous variation of pact, pƔ, pk, and ptot during push-off with positive loads were closer to 0% than with negative loads. As the load increased, maximum values of ptot, pƔ, and pk decreased. Only with a negative load of -30% did ptot increase significantly, this was not accompanied by changes in pact, pƔ, and pk. The load of one's own body provides conditions for develop high pact peaks, although the maximum ptot is not achieved in that condition. The increase in negative loads produces a significant increase in ptot, but not in pact and can be interpreted as a situation in which the power delivered to the system by the action of active components is better used. The SJ with positive load, although more similar to the instantaneous changes that occur to the SJ with body weight are not gestures where high power is developed.

Differences in the utilisation of active power in squat and countermovement jumps.

The aim of this article was to understand how active power is used in squat and countermovement jumps. A simple empirical model comprising a mass, a spring, an active element and a damper, together with an optimisation principle, was used to identify the mechanical factors that maximise performance of jumps without countermovement (squat jumps, SJ) and with countermovement (CMJ). Twelve amateur volleyball players performed SJ from two initial positions and CMJ with two degrees of counterbalancing, while kinematic data were collected (jump height, push-off duration and position of the centre of mass). The model adjusted well to real data of SJ through all the impulse phase, and slightly less adequately at the end of this phase for CMJ. Nevertheless, it provides a satisfactory explanation for the generation and utilisation of active power for both type of jumps. On average, the estimated power of the active elements, the spring, and the damper were greater in the SJ. Based upon the result obtained with this model, we suggest that active power is best evaluated with SJ. The reason for this is that, during this kind of jump, the elements associated with the damper consume much of the energy produced by the active elements. The participation of the elements that consume the energy generated by the active elements is less in CMJ than in SJ, allowing for a better utilisation of this energy. In this way it is possible to achieve a better performance in CMJ with less active power.

Evaluacion del equilibrio durante la marcha a velocidad autoseleccionada en jovenes saludables, adultos mayores no caedores y adultos mayores con alto riesgo de caidas / Assessment of balance during gait at a self-elected speed in healthy youngsters, elderly persons who do not fall and elderly persons with a high risk of falls

Introduccion: el equilibrio depende de mantener la proyeccion del centro de masa corporal dentro de los limites de la base de sustentacion, pero su valoracion se realiza habitualmente en forma indirecta a traves de la variabilidad cinematica. Objetivos: analizar el equilibrio durante la marcha a velocidad autoseleccionada en tres poblaciones de sujetos utilizando diferentes abordajes. Material y metodo: los grupos analizados fueron: jovenes saludables, adultos mayores no caedores y adultos mayores caedores. Mediante analisis cinematico tridimensional se calculo: velocidad, variabilidad temporal, variabilidad angular de rodilla y el equilibrio duranteciclos de marcha. Para el calculo directo del equilibrio se definio una variable considerando la proyeccion del centro de masa corporal y la base de sustentacion. Los resultados de las variables cinematicas fueron comparados entre los grupos mediante ANOVA (alfa=0,05). Deigual forma se procedio con los valores medio, maximo y minimo de la estimacion directa del equilibrio entre grupos para las fases de apoyo simple y doble del ciclo. Resultados: la velocidad de ciclo fue similar entre los adultos mayores. En los jovenes saludables la variabilidad temporal del ciclo fue baja y la variabilidad angular de rodilla alta y estas variables no mostraron diferencias entre los grupos de adultos mayores. Durante tamla fase de apoyo simple los valores medio y minimo de equilibrio para el grupo de caedores fueron significativamente diferentes respecto a los demas grupos. Conclusiones: la estimacion directa del equilibrio durante la fase de apoyo simple surge como una potencial herramienta para la identificacion de individuos con riesgo de caida.

Introduction: balance depends on keeping the projection of the center of body mass within the limits of the support basis, although its assessment is usually performed by means of cinematic variability. Objectives: to analyse balance during gait at a selfelected speed in three populations using different approaches. Method: the groups analysed were: healthy youngsters, elderly who do not fall and elderly who fall. We calculated speed, time variability, angle variability of knee and balance during gait cycles through a tridimensional cinematic analysis. To directly calculate balance we defineda variable considering the projection of the center of body mass. Results of the cinematic variables were compared between groups using ANOVA (a=0,05). Similarly we compared average, maximum and minimum values ofthe direct balance estimation between groups for simple support and double cycle stages. Results: cycle speed was similar in elderly persons. Time variability of cycle was low and angle variability was high in healthy youngsters, while these variables evidenced no difference between the elderly persons groups. During the simple support stage average and minimum balance values for the group of people who fall were significantly different if compared to the other groups. Conclusions: direct estimation of balance during the simple support stage appears as a potential tool to identify individuals with a risk of falls.

Introdução: o equilibrio depende da manutenção da projeção do centro de massa corporea dentro dos limitesda base de apoio, mas sua avaliação é feita habitualmente de maneira indireta utilizando variabilidade cinematica. Objetivos: analisar o equilibrio durante a marcha em velocidade auto-selecionada em tres populações de pessoas utilizando diferentes abordagens. Material e metodo: os grupos analisados foram: jovens saudaveis, adultos idosos não caidores e adultos idosos caidores. Utilizando analise cinematica tridimensional foram calculadas a velocidade, a variabilidade temporal, avariabilidade angular do joelho e o equilibro durante os ciclos da marcha. Para fazer o calculo direto do equilibrio definiu-se uma variavel considerando a projeção do centro de massa corporea e a base de apoio. A comparação entre os resultados das variaveis sistematicas entre os grupos foi feita usando ANOVA (a=0,05) e tambem para comparar os valores minimo, medio e maximo da estimativa direta para as fases de apoio simples e duplo do ciclo. Resultados: a velocidade de ciclo foi similar entre os dois grupos de idosos. No grupo de jovens saudaveis a variabilidade temporal do ciclo foi baixa e a variabilidade angular do joelho alta e não se encontraram diferenças nessas variaveis entre os dois grupos de idosos. Durante a fase de apoio simples os valores medio e minimo de equilibrio para o grupo de caidores foram significativamente diferentes quando comparados com os outros grupos. Conclusões: a estimativa direta do equilibrio durante a fase de apoio simples pode ser uma ferramenta potencial para a identificação de individuos com risco de queda.