No abstract

During rapid movements, tendons can act like springs, temporarily storing work done by muscles and then releasing it to power body movements. For some activities, such as frog jumping, energy is released from tendon much more rapidly than it is stored, thus amplifying muscle power output. The period during which energy is loaded into a tendon by muscle work may be aided by a catch mechanism that restricts motion, but theoretical studies indicate that power can be amplified in a muscle-tendon load system even in the absence of a catch. To explore the limits of power amplification with and without a catch, we studied the bullfrog plantaris muscle-tendon during in vitro contractions. A novel servomotor controller allowed us to measure muscle-tendon unit (MTU) mechanical behavior during contractions against a variety of simulated inertial-gravitational loads, ranging from zero to 1× the peak isometric force of the muscle. Power output of the MTU system was load dependent and power amplification occurred only at intermediate loads, reaching ∼1.3× the peak isotonic power output of the muscle. With a simulated anatomical catch mechanism in place, the highest power amplification occurred at the lowest loads, with a maximum amplification of more than 4× peak isotonic muscle power. At higher loads, the benefits of a catch for MTU performance diminished sharply, suggesting that power amplification >2.5× may come at the expense of net mechanical work delivered to the load.

No abstract

In this work, a model of a rider and snowboard is presented. The snowboard is modelled as two rigid one-dimensional sections connected by a frictionless pin-joint linked by a torsional stiffness and the rider by a mass at a fixed height above the snowboard, which can move longitudinally. The model is simplified to allow the fundamental behaviour of the snowboard and rider to be investigated for a number of manoeuvres used by learners. The behaviour of the rider is shown to be related to the angle of lean and it is conjectured that the rider might attempt to achieve consistency of response by moving their centre of mass longitudinally. The response of the model in open-loop is difficult to control, and to overcome this, two control loops are designed for the lateral velocity and yaw angle of the snowboard. The model is shown to recreate a number of manoeuvres that are used to help people to learn to ride snowboards.