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Torque patterns of the limbs of small therian mammals during locomotion on flat ground

Hartmut Witte^*, Jutta Biltzinger, Rémi Hackert, Nadja Schilling, Manuela Schmidt, Christian Reich and Martin S. Fischer

Institut für Spezielle Zoologie und Evolutionsbiologie, Friedrich-Schiller-Universität Jena, Erbertstraße 1, D-07743 Jena, Germany

View larger version (45K): [in a new window]   Fig. 1. The four long segments of a mammalian extremity. Forelimb: scapula, upper arm, lower arm and hand, linked to the proximal segment by scapular fulcrum, shoulder joint, elbow joint and wrist joint. Hindlimb: thigh, shank, foot and toes, linked to the proximal segment by hip joint, knee joint, ankle joint and metatarsophalangeal (intratarsal) joint.

View larger version (155K): [in a new window]   Fig. 2. Range for the possible lines of actions of ground reaction forces (GRF) in a pika (Ochotona rufescens) during half-bound. The Center of Pressure (CoP) may be located anywhere under the sole of the foot. The effects are illustrated for one forelimb (A) and one hindlimb (B).

View larger version (59K): [in a new window]   Fig. 3. Sensitivity analysis: effect of the possible mislocation of the center of pressure CoP in Ochotona rufescens illustrated in Fig. 2 on the torques in the joints shown in Fig. 1. Graphs are given for a half-bounding pika for assumed locations of the CoP under tip of toe and heel (thin lines) and mid-sole (thick lines).

View larger version (48K): [in a new window]   Fig. 4. Ground reaction forces (GRF) in Galea musteloides, Ochotona rufescens and Tupaia glis, measured in the 29 trials used for inverse dynamic analysis. Left, horizontal forces, positive values indicate forces acting in the direction of propulsion; right, vertical forces. (A) Forelimbs; (B) hindlimbs.

View larger version (36K): [in a new window]   Fig. 5. Components of net joint forces in a half-bounding pika (Ochotona rufescens). Left, forelimbs; right, hindlimbs; top, horizontal; bottom, vertical.

View larger version (64K): [in a new window]   Fig. 6. Torques acting in the main joints of the extremities of a sample of cuis (Galea musteloides) during cyclic locomotion. Left, forelimbs; right, hindlimbs. According to a Kolmogorov—Smirnov test, the torques for each relative stance time may be assumed to be normally distributed (P<0.01; N=7).

View larger version (52K): [in a new window]   Fig. 7. Proportion of the torques caused by ground reaction forces (GRF) in relation to net joint torques in a half-bounding pika (Ochotona rufescens).

View larger version (63K): [in a new window]   Fig. 8. Torque patterns in the main joints of the extremities of cuis (Galea musteloides; triangles, N=7), pikas (Ochotona rufescens; circles, N=3 for forelimb, 4 for hindlimb) and tree shrews (Tupaia glis; squares, N=2 for forelimb, 5 for hindlimb) during cyclic locomotion. Torques are normalised with reference to body weight (BW). (A) Forelimb, (B) hindlimb. Significant differences (P<0.01, Student's t test) are noted by asterisks and letters a—f.

View larger version (28K): [in a new window]   Fig. 9. Dynamics of forelimb motion in the cui (Galea musteloides). For seven evenly distributed events during the stance phase, the figure illustrates: the (reactive) net joint forces as vectors; the net joint torques as circle segments, virtually attached to the segment distal of the joint and indicating the rotational tendency by its orientation relative to the segment; and the length of the muscle bellies of M. triceps brachii relative to their length at touch down.

View larger version (58K): [in a new window]   Fig. 10. Torque patterns in the main joints of the extremities of cat (Perell et al., 1988; Fowler et al., 1993), dog (Dogan et al., 1991), goat (Pandy et al., 1988) and horse (Colborne et al., 1997; Clayton et al., 1998) in comparison with the torque patterns of small mammals. (A) Forelimb, (B) hindlimb. Torques are normalised (to 1.0) to a comparable integral of the graph.