Study of technical, normative, and narrative medieval literature and of archaeological pieces allows the motor skills of armoured members of the aristocracy to be outlined but not quantified. The authors present novel data on the impact of wearing armour on both the freedom of movement and the energy cost of locomotion, and confront the results to systematic analysis of medieval written sources. An accurate harness replica realized in an informed archaeological experimental way, close to medieval material and manufacturing conditions, was used for the experiments. Measurements of the energy cost of locomotion in and out of armour were taken during walking and running on a treadmill. Gait analysis and range of motion of joints were performed with 3-D kinematics. The results indicated an increase in the energy cost of locomotion in slight excess to the added weight and for most movements studied reductions in the range of motion over the joint, potentially to the advantage of the wearer during combat. This proof of concept appears promising for further study in this field of scholarly endeavor.