Study of animal locomotion

Below highlights the key kinematic parameters used to quantify body and limb movement for different modes of animal locomotion.

[1][2] To quantify the intralimb kinematics and interlimb coordination during walking, the stance and swing phases of the step cycle must be isolated.

[6][7][8][9] After extracting the positions of each leg throughout a recording, there are several ways of determining the stance and swing phases of the step cycle.

One approach involves using peak and trough detection of the leg tip positions in ego-centric coordinates and after the animal has been aligned to a common heading (Fig.

Static stability: minimum distance from the center of mass (COM) to any edge of the support polygon created by the legs in stance for each moment in time.

Therefore, the continuous variability in coordination patterns across walking speeds and across individual flies can be visualized in a low dimensional embedding,[8] using techniques such as principal components analysis and UMAP.

Robustness refers to how much offset in the timing of a legs stance can be tolerated before the fly becomes statically unstable.

For instance, a robust gait may be particularly important when traversing uneven terrain, as it may cause unexpected disruptions in leg coordination.

Analyses suggest that flies may exhibit a compromise between the most stable and most robust gait at a given walking speed.

[16][17][18] An interlimb kinematic parameter that is commonly speed dependent is gait, the stepping pattern across legs.

Optogenetic perturbations are also frequently combined with kinematics to study how locomotor behaviors and tasks are affected by the activity of a certain group of neurons.

Observations resulting from optogenetic experiments may provide insight into the neural circuitry that underlies different locomotor behaviors.

Models of animal locomotion are important for gaining new insights and predications on how kinematics arise from the interactions of the nervous, skeletal, and/or muscular systems that would otherwise be difficult to glean from experiments.

Figure 1. Classifying stance and swing transitions of the front right (red) and left (blue) legs of a fly. The onset of stance (black dot) occurs at the peaks of the leg position signal, whereas, the onset of swing (light blue dot) occurs at the troughs.
UMAP embedding of leg joint angle kinematics in walking fruit flies. The variability across individual flies is shown by their distinct clustering (C), yet their coordination patterns are similar (D). [ 8 ]
Documentary film, shot at 1200 fps, used to study the locomotion of a cheetah. The end of the video shows the methods used for filming.
A fruit fly, Drosophila melanogaster , tethered and walking on a spherical treadmill. Slowed 6X.
Simultaneous measurement of ground forces (blue) and kinematics such as petiole trajectories (red) and stepping pattern (yellow) of walking desert ants in a laboratory environment in order to describe the alternating tripod gait. Recording rate: 500 fps, Playback rate: 10 fps.