A method of evaluating fatigue in a hair fibre sample includes receiving fatigue testing data for the hair fibre sample for a plurality of loading cycles, in which the fatigue testing data comprises force or stress against displacement or strain data. The method also includes determining, for at least a subset of the loading cycles, a loading energy based on data from the fatigue testing data. The method also includes determining an indication of fatigue in the hair fibre sample based on the loading energy of the at least a subset of the loading cycles.