Distance moved
Definition
The distance traveled by the center, nose or tail-base point of the subject from the previous sample to the current one. It is calculated as:
where:
▪DMk = Distance moved from sample k–1 to sample k
▪Xk-1, Yk-1 = X,Y coordinates of the center, nose or tail-base point at sample k-1,
▪Xk, Yk = X,Y coordinates of the center, nose or tail-base point at sample k-1.
1.Click Add next to Distance moved.
2.Complete the procedure to add the variable. See Calculate statistics: procedure.
Notes
▪If your experiment is set to Center-point, nose-point and tail-base detection, click the Body points tab and select the body points for which you want to calculate the distance.
▪Because it is based on change in X,Y coordinates, Distance moved needs two valid (non-missing) samples. A missing sample in your track results in missing Distance moved values in that and in the next sample. Make sure that the proportion of missing samples is low (less than 1%).
▪Sample rate influences the values of Distance moved. When tracking at too low a sample rate, parts of the actual path are cut off, resulting in an underestimation of per-sample (and total) Distance moved. If, on the other hand, the sample rate is too high, EthoVision XT catches the wobbling of the body's center point of the walking animal, causing extra apparent movement, and therefore an overestimation of per-sample (and total) Distance moved. See Track Smoothing for a description of how to filter out small movements.
Distance moved is often used to give a general measure of activity. It is also used as the basis for calculating other parameters such as velocity (see below).
In rodent models of aging, the total and maximum distance moved are used to calculate the frailty index. See Parks et al. (2012) J. Gerontol. A 67(3): 217-227.