Systems and methods for detecting environmental forces on an elongate device

A medical device includes a flexible elongate instrument, an actuator for inserting and retracting the instrument, and a control unit configured to determine at least one of a force being exerted by the actuator or an amount of force applied at a proximal end of the instrument. The control unit is configured to determine a force exerted by the instrument on tissue of a patient based on a shape of the instrument and at least one of the force exerted by the actuator or the force applied at the proximal end. A method of operating a medical device includes: determining a shape of a flexible elongate instrument and at least one of a first force exerted by an actuator or a second force applied to a proximal end; and determining a third force, exerted on tissue, based on the shape and at least one of the first or second forces.