Abstract
There is a high risk of serious injury to the lower limbs in a human drop landing. However, cats are able to jump from the same heights without any sign of injury, which is attributed to the excellent performance of their limbs in attenuating the impact forces. The bionic study of the falling cat landing may therefore contribute to improve the landing-shock absorbing ability of lower limbs in humans. However, the contributions of cat limb joints to energy absorption remain unknown. Accordingly, a motion capture system and plantar pressure measurement platform were used to measure the joint angles and vertical ground reaction forces of jumping cats, respectively. Based on the inverse dynamics, the joint angular velocities, moments, powers, and work from different landing heights were calculated to expound the synergistic mechanism and the dominant muscle groups of cat limb joints. The results show that the buffering durations of the forelimbs exhibit no significant difference with increasing height while the hindlimbs play a greater role than the forelimbs in absorbing energy when jumping from a higher platform. Furthermore, the joint angles and angular velocities exhibit similar variations, indicating that a generalized motor program can be adopted to activate limb joints for different landing heights. Additionally, the elbow and hip are recognized as major contributors to energy absorption during landing. This experimental study can accordingly provide biological inspiration for new approaches to prevent human lower limb injuries.
Highlights
Cats are generally acknowledged to have excellent landing buffering capacities, achieved through natural selection, and have received significant scientific attention
Double-peak patterns were found at all jump heights, which was consistent with the findings of a previous study [15]
The ratio of the peak vertical ground reaction forces (VGRFs) of the right hind (RH) limb to the total force increased with the increase in jump height, indicating that the hindlimbs experience a greater peak VGRF than the forelimbs when the cat jumps from a higher height
Summary
Cats are generally acknowledged to have excellent landing buffering capacities, achieved through natural selection, and have received significant scientific attention. As the saying goes: cats have nine lives, emphasizing the fact that cats have an extraordinary ability to survive falls In terms of this phenomenon, a number of researchers have studied the body posture of cats as they fall, using high-speed cameras, and the results show that falling cats make gyroscopic turns such that their forelimbs and hindlimbs land successively, regardless of the cat’s orientation at the start of the fall [2,3,4]. It has been suggested that cat limbs play a significant role in dissipating the impact forces during landing. The responses of the elbow extensors to ground reaction forces (GRFs) have been studied, showing that, for a given cat, both the vertical and horizontal GRFs increase with jump height while torque values at the elbow joint do not change significantly [10]. The manner of distribution of impact forces between the forelimbs and hindlimbs of cats has been found to be related to the jump height, and the hindlimbs have been found to play an increasing role in the absorption of energy with increasing jump height [12]
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