4) Active marker systems are similar to the passive marker system but use "active" markers. These markers are triggered by the incoming infra red signal and respond by sending out a corresponding signal of their own. This signal is then used to triangulate the location of the marker. The advantage of this system over the passive one is that individual markers work at predefined frequencies and therefore, have their own "identity". This means that no post-processing of marker locations is required, however the systems tend to be less forgiving for out-of-view markers than the passive systems.

Therefore, a typical modern gait lab has several cameras (video or infra-red) placed around a walkway or treadmill, which are linked to a computer. The patient has markers applied to anatomical landmark points, which are mostly palpable bony landmarks such as the iliac spines of the pelvis, the malleoli of the ankle, and the condyles of the knee. The patient walks down the walkway or on the treadmill and the computer calculates the trajectory of each marker in three dimensions. A model is applied to compute the underlying motion of the bones. This gives a full breakdown of the motion at each joint.

In addition, to calculate movement kinetics, most labs have floor load transducers, also known as force-plates, which measure the ground reaction force, including both magnitude and direction. Adding this to the known dynamics of each body segment, enables the solution of equations based on Newton's laws of motion and enables the computer to calculate the forces exerted by each muscle group, and the net moment about each joint at every stage of the gait cycle. The computational method for this is known as inverse dynamics.

This use of kinetics however does not result in information for individual muscles but muscle groups, such as the extensor or flexors of the limb. To detect the activity and contribution of indivudual muscles to movement, it is necessary to investigate the electrical activity of muscles. Some labs also use surface electrodes attached to the surface of the skin to detect the activity of for example the muscle of the leg. In this way it is possible to investigate the activation times of muscles and to some degree the magnitude of their activation and thereby assess their contribution to gait. Deviations from normal kinematic, kinetic or EMG patterns are used to diagnose specific conditions and predict the outcome of treatment.