Leg fold represents a numerical representation of the angle of the legs (ankle-knee-pelvis angle). Near the maximum value, the legs are fully extended, and near the minimum value, the legs are folded. 

To calculate the frame length, count the total number of frames in the dataset. Each frame represents a data point collected over time. The total frame length gives the duration of the motion or activity being analyzed. In this dataset, the total frame length is determined by the number of entries in the data array.