Robot-aided treadmill training is an innovative rehabilitation method for patients with locomotor dysfunctions. However, in current rehabilitation systems treadmill speed is restricted to constant values or adjusted by the therapist, whereas self-determined phases of accelerations and decelerations cannot be performed by the patient in an interactive and intuitive way. We present a new approach that allows treadmill walking with intuitive gait speed adaptation. In this approach, the user's

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... position is fixed in walking direction. The horizontal interaction forces applied by the user intending to accelerate or decelerate the gait are measured at the trunk connection and fed to the treadmill controller. The desired gait acceleration is calculated by means of a virtual admittance. Integration yields the desired speed which is fed into the underlying velocity controller of the treadmill. The method was verified by two experimental setups and tested on ten healthy subjects. In one setup, the subject's trunk was rigidly connected by a tether, whereas in the second setup the subject was placed in a robotic gait orthosis. All subjects were able to use both systems immediately and intuitively. The treadmill speed profile during the gait cycle corresponds to that of normal walking. The controller can be extended to simulate different walking conditions, such as slope walking. The method can be used for patient-cooperative control strategies performed with a robotic gait orthosis as well as for any other user-interactive applications in fitness and sports.