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A mechanical link model of two-toed sloths: no pendular mechanics during suspensory locomotion

100%

Nyakatura J. A., Andrada E.

Acta Theriologica

2013

tom 58

nr 1

Sloths are morphologically specialized in suspensory quadrupedal locomotion and posture. During steady-state locomotion they utilize a trot-like footfall sequence. Contrasting the growing amount of published accounts of the functional morphology and kinematics of sloth locomotion, no study concerned with the dynamics of their quadrupedal suspensory locomotion has been conducted. Brachiating primates have been shown to travel at low mechanical costs using pendular mechanics, but this is associated with considerable dynamic forces exerted onto the support. To test whether sloth locomotion can be described by simple connected pendulum mechanics, we analyzed the dynamics of sloth locomotion with use of a mechanical segment link model. The model integrates the body segment parameters and is driven by kinematic data with both segment parameters and kinematic data obtained from the same sloth individual. No simple pendular mechanics were present. We then used the model to carry out an inverse dynamic analysis. The analysis allowed us to estimate net limb joint torques and substrate reaction forces during the contact phases. Predominant flexing limb joint torque profiles in the shoulder, elbow, hip, and knee are in stark contrast to published dominant extensor torques in the limb joints of pronograde quadrupedal mammals. This dissimilarity likely reflects the inverse orientation of the sloth towards the gravity vector. Nevertheless, scapular pivot and shoulder seem to provide the strongest torque for progression as expected based on unchanged basic kinematic pattern previously described. Our model predicts that sloths actively reduce the dynamical forces and moments that are transmitted onto the support. We conclude that these findings reflect the need to reduce the risk of breaking supports because in this case sloths would likely be unable to react quickly enough to prevent potentially lethal falls. To achieve this, sloths seem to avoid the dynamical consequences of effective pendular mechanics.

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Impact testing of biological material on the example of apple tissue

84%

Golacki K., Kolodziej P.

Teka Komisji Motoryzacji i Energetyki Rolnictwa

2011

tom 11C

The study presents the measuring position for determination of the dynamical behavior of vegetables and fruit. The main element of the device is an instrumented rigid physical pendulum made of carbon fi ber. The pendulum arm was developed as a double arch connected with the external links. This construction enables attaining the desirable value of the quotient of the mass moment of inertia of the pendulum arm with a fruit and the arm without it as well as appropriate rigidity. The studies with the pendulum device application simulated the apple drop from a required height. The tests measuring pendulum rotation angle and fruit response force in time facilitated determination of the force – displacement correlation at impact event. The obtained displacement and impact force courses in time were presented graphically.

Ograniczanie wyników

1 Acta Theriologica

1 Teka Komisji Motoryzacji i Energetyki Rolnictwa

1 Andrada E.

1 Golacki K.

1 Kolodziej P.

1 Nyakatura J. A.

1 2013

1 2011

Wyniki wyszukiwania

A mechanical link model of two-toed sloths: no pendular mechanics during suspensory locomotion

Impact testing of biological material on the example of apple tissue