A Dynamics and Stability Framework for Avian Jumping Take-off

Jumping take-off in birds is an explosive behaviour with the goal of providing a rapid transition from ground to airborne locomotion. An effective jump is predicated on the need to maintain dynamic stability through the acceleration phase. The present study concerns understanding how birds retain control of body attitude and trajectory during take-off. Cursory observation suggests that stability is achieved with relatively little cost. However, analysis of the problem shows that the stability margins during jumping are actually very small and that stability considerations play a significant role in selection of appropriate jumping kinematics. We use theoretical models to understand stability in prehensile take-off (from a perch) and also in non-prehensile take-off (from the ground). The primary instability is tipping, defined as rotation of the centre of gravity about the ground contact point. Tipping occurs when the centre of pressure falls outside the functional foot. A contribution of the paper is the development of graphical tipping stability margins for both centre of gravity location and acceleration angle. We show that the nose-up angular acceleration extends stability bounds forward and is hence helpful in achieving shallow take-offs. The stability margins are used to interrogate simulated take-offs of real birds using published experimental kinematic data from a guinea fowl (ground take-off) and a diamond dove (perch take-off). For the guinea fowl the initial part of the jump is stable, however simulations exhibit a stuttering instability not observed experimentally that is probably due to absence of compliance in the idealised joints. The diamond dove model confirms that the foot provides an active torque reaction during take-off, extending the range of stable jump angles by around 45{\deg}.Comment: 21 pages, 11 figures; supplementary material: https://figshare.com/s/86b12868d64828db0d5d; DOI: 10.6084/m9.figshare.721056

Kinetic and temporal correlates to skillfulness in vertical jumping

Vertical ground reaction forces of countermovement jumps with armswing (CMWA) were examined to determine kinetic and temporal strategies related to skillfulness in vertical jumping. Effective integration of the system (EIS) was introduced to examine skillfulness separate from the influences of genetic talent or training. Vertical jump height was considered susceptible to both genetic talents and extensive training. Kinetic and temporal variables from force-time curves of 51 subjects were evaluated for their relationship to skillfulness using both EIS and vertical jump height. It was hypothesized that more of the variance in EIS could be explained by kinetic and temporal variables than by vertical jump height. A second purpose of this investigation was to examine the effects of standardizing force-time curves mathematically to produce a smooth rise to a single peak force. Smooth rises to peak force were attained by fitting a parabolic trajectory to the force record. It was hypothesized that EIS scores and vertical jump heights would improve as a result of the standardization process. Results of this investigation did not fully support the hypothesis that more variance in skillfulness could be explained when skillfulness was determined by EIS

Are Torque-Driven Simulation Models of Human Movement Limited by an Assumption of Monoarticularity?

Subject-specific torque-driven computer simulation models employing single-joint torque generators have successfully simulated various sports movements with a key assumption that the maximal torque exerted at a joint is a function of the kinematics of that joint alone. This study investigates the effect on model accuracy of single-joint or two-joint torque generator representations within whole-body simulations of squat jumping and countermovement jumping. Two eight-segment forward dynamics subject-specific rigid body models with torque generators at five joints are constructed—the first model includes lower limb torques, calculated solely from single-joint torque generators, and the second model includes two-joint torque generators. Both models are used to produce matched simulations to a squat jump and a countermovement jump by varying activation timings to the torque generators in each model. The two-joint torque generator model of squat and countermovement jumps matched measured jump performances more closely (6% and 10% different, respectively) than the single-joint simulation model (10% and 24% different, respectively). Our results show that the two-joint model performed better for squat jumping and the upward phase of the countermovement jump by more closely matching faster joint velocities and achieving comparable amounts of lower limb joint extension. The submaximal descent phase of the countermovement jump was matched with similar accuracy by the two models (9% difference). In conclusion, a two-joint torque generator representation is likely to be more appropriate for simulating dynamic tasks requiring large joint torques and near-maximal joint velocities.N/

From standing posture to vertical jump - Experimental and model analysis of human movement

Dalla postura eretta al salto verticale - Analisi sperimentale e modellistica del movimento uman