According to Jorge L. Reyes-Ortiz, Davide Anguita, Alessandro Ghio and Luca Oneto, and as described in the url for the raw data: https://d396qusza40orc.cloudfront.net/getdata%2Fprojectfiles%2FUCI%20HAR%20Dataset.zip, the variables in this database come from the accelerometer and gyroscope 3-axial raw signals tAcc-XYZ and tGyro-XYZ