Meeting Abstract
During a jump, many animals enhance the power that is generated by their muscles as energy is transferred to accelerate their body’s center of mass. We call this phenomenon power amplification. Historically, computational models demonstrated that tendons in-series with muscles enhance the rate of energy transfer. However, when we incorporated realistic muscle state properties (length-tension and force-velocity relationships) into similar models the amount of power transferred to a load was greatly limited. Yet, we know frogs, overcome limitations set by muscle through 1) morphological adaptations 2) pre-stretch of muscles and 3) catch systems that allow a muscle to store energy in tendons and aponeuroses. We explored these strategies with a Simulink Matlab model of a Hill-type muscle-tendon unit with inertial and gravitational loads. In this model, we swept a wide parametric space of tendon stiffnesses, effective mechanical advantages and pre-stretch conditions. We observed that at low mechanical advantages (EMA=0.12) there are more limited combinations of tendon stiffness and body mass where the power of the muscle transferred to the load is enhanced. However, if the effective mechanical advantage is larger (EMA = 0.3), there is a broader morphological space in which power amplification exists. In all conditions, pre-stretching the muscle-tendon unit increases the power transferred to the load because stretching “cheats” the system by adding initial energy and allowing muscle shortening onto, rather than away from the plateau of the length-tension curve. This computational approach allows us to understand the limits of the building blocks of power amplifying systems. Furthermore, this approach could help develop guidelines for actuating wearable devices capable of augmenting human performance during accelerative movements like jumping or sprinting.
