Extremity speed represents the speed of movement of the end joints of the limbs (both wrists, ankles). Near the maximum value, the faster the speed of the extremities, near the minimum value, the less movement of the extremities. 

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.