Measuring method for determining the length conditions, the position and/or the radius of movement of the lower extremities of a bedridden patient, such as hip joint, knee joint and/or upper leg, in which method - at least one knee module of a rehabilitation mechanism is operatively connected to a leg of the patient via an application point; - a measuring device is used for recording and/or determining a trajectory (T n; T n+1) solely of the application point during a movement of the leg with the knee module of the rehabilitation mechanism; and - a model-generating means is used to create, from the data thus obtained, a kinematic model of the length conditions, the position and/or the radius of movement of at least parts of the lower extremities of the patient; wherein, - in at least one method step, determined coordinate pairs (Y 1 / Z 1, Y 2 / Z 2,..., Y n / Z n) or coordinate triplets (Y 1 / Z 1 / t 1; Y 2 / Z 2 / t 2;.../...; Y n / Z n / t n) are compared with a model function in the form of a coordinate equation, and in this way, in the context of a curve-fitting, the position (Y H (t) / Z H (t)) of a rotation point and/or the length (L o) between application point and rotation point of the bedridden patient, and an angle (θ_DP) between two points on the trajectory (T n; T n+1) and the rotation point are determined; wherein the following are used: - as model function, in particular the coordinate equation Y n − M Y Y H 2 L 0 2 + Z n − M Z Z H 2 L 0 ± ΔL 2 = 1 for an ellipse; - as parameter for the center point of the ellipse, a function (M Y (Y H); M Z (Z H)) according to the position (Y H (t) / Z H (t)) of the rotation point; and - as semi-major axis of the ellipse, the length (L o) between application point and rotation point of the bedridden patient, wherein the term (L 0 ±ΔL) describes a possible shift of the position (Y H (t) /Z H (t)) of the rotation point during a movement. - at least one knee module of a rehabilitation mechanism is operatively connected to a leg of the patient via an application point; - a measuring device is used for recording and/or determining a trajectory (T n; T n+1) solely of the application point during a movement of the leg with the knee module of the rehabilitation mechanism; and - a model-generating means is used to create, from the data thus obtained, a kinematic model of the length conditions, the position and/or the radius of movement of at least parts of the lower extremities of the patient; wherein, - in at least one method step, determined coordinate pairs (Y 1 / Z 1, Y 2 / Z 2,..., Y n / Z n) or coordinate triplets (Y 1 / Z 1 / t 1; Y 2 / Z 2 / t 2;.../...; Y n / Z n / t n) are compared with a model function in the form of a coordinate equation, and in this way, in the context of a curve-fitting, the position (Y H (t) / Z H (t)) of a rotation point and/or the length (L o) between application point and rotation point of the bedridden patient, and an angle (θ_DP) between two points on the trajectory (T n; T n+1) and the rotation point are determined; wherein the following are used: - as model function, in particular the coordinate equation Y n − M Y Y H 2 L 0 2 + Z n − M Z Z H 2 L 0 ± ΔL 2 = 1 for an ellipse; - as parameter for the center point of the ellipse, a function (M Y (Y H); M Z (Z H)) according to the position (Y H (t) / Z H (t)) of the rotation point; and - as semi-major axis of the ellipse, the length (L o) between application point and rotation point of the bedridden patient, wherein the term (L 0 ±ΔL) describes a possible shift of the position (Y H (t) /Z H (t)) of the rotation point during a movement. - as model function, in particular the coordinate equation Y n − M Y Y H 2 L 0 2 + Z n − M Z Z H 2 L 0 ± ΔL 2 = 1 for an ellipse; - as parameter for the center point of the ellipse, a function (M Y (Y H); M Z (Z H)) according to the position (Y H (t) / Z H (t)) of the rotation point; and - as semi-major axis of the ellipse, the length (L o) between application point and rotation point of the bedridden patient, wherein the term (L 0 ±ΔL) describes a possible shift of the position (Y H (t) /Z H (t)) of the rotation point during a movement.