The analysis of the dynamics of pathological motion can provide new and meaningful knowledge about musculoskeletal disorders. The application of the study of pathological ambulation to the analyses of clinical problems is analyzed and discussed. The importance of the selection of appropriate measurement protocols and variable selection is illustrated using an example of the evaluation of patients with an anterior cruciate deficient knee. In particular, the importance of the joint moment as a measure of normal and pathological ambulation is described. An example is provided from a study based on the analysis of 16 patients with unilateral anterior cruciate deficiency. Patients were studied during walking, jogging and ascending and descending stairs. The results are used to demonstrate the importance of testing activities of the knee (e.g. walking, jogging, stair-climbing) that stress the knees during different ranges of motion in order to differentiate functional adaptation associated with the anterior cruciate deficient knee. Results demonstrate that functional abnormalities occur during low stress activities such as level walking. Further, it appears that the functional adaptation occurring during these activities is associated with the anterior force generated on the tibia when the quadriceps contract and the knee is near full extension. It appears that locomotion patterns are reprogrammed to produce an adaptive gait in the majority of patients with anterior cruciate deficient knees.