A monitoring and/or therapy apparatus (200, 300, 320, 320'), comprising: A contact layer (202, 302, 322, 322') comprising a stretchable or substantially stretchable substrate configured to be attached to a user's joint; at least one strain sensor (500, 520, 540) coupled with the contact layer (202, 302, 322, 322'); electronic circuitry electronically coupled with the at least one strain sensor, the electronic circuitry configured to determine an amount of an elongation of the at least one strain sensor based on a change in a resistance of the at least one strain sensor (500, 520, 540); and a source of negative pressure configured to be in fluid communication with a space under the contact layer (202, 302, 322, 322') and to supply negative pressure to the space; wherein: the at least one strain sensor (500, 520, 540) comprises a plurality of stretchable tracks (204, 304, 324, 324') positioned on the substrate; the resistance of the at least one strain sensor increases as at least some tracks of the plurality of stretchable tracks are elongated due to the contact layer being elongated; the electronic circuitry is configured to determine an angle and/or a range of movement of the joint responsive to changes in the resistance of the at least one strain sensor (500, 520, 540); wherein the electronic circuitry comprises a machine-readable memory configured to record information related to an elongation of the at least one strain sensor; the electronic circuitry is configured to automatically collect data from the strain sensor at a predetermined frequency; and the apparatus further comprises a temperature sensor, wherein the temperature sensor is configured to provide to the electronic circuitry an electrical signal related to a temperature of the strain sensor and/or a temperature of a region of the substrate adjacent to the strain sensor. A contact layer (202, 302, 322, 322') comprising a stretchable or substantially stretchable substrate configured to be attached to a user's joint; at least one strain sensor (500, 520, 540) coupled with the contact layer (202, 302, 322, 322'); electronic circuitry electronically coupled with the at least one strain sensor, the electronic circuitry configured to determine an amount of an elongation of the at least one strain sensor based on a change in a resistance of the at least one strain sensor (500, 520, 540); and a source of negative pressure configured to be in fluid communication with a space under the contact layer (202, 302, 322, 322') and to supply negative pressure to the space; wherein: the at least one strain sensor (500, 520, 540) comprises a plurality of stretchable tracks (204, 304, 324, 324') positioned on the substrate; the resistance of the at least one strain sensor increases as at least some tracks of the plurality of stretchable tracks are elongated due to the contact layer being elongated; the electronic circuitry is configured to determine an angle and/or a range of movement of the joint responsive to changes in the resistance of the at least one strain sensor (500, 520, 540); wherein the electronic circuitry comprises a machine-readable memory configured to record information related to an elongation of the at least one strain sensor; the electronic circuitry is configured to automatically collect data from the strain sensor at a predetermined frequency; and the apparatus further comprises a temperature sensor, wherein the temperature sensor is configured to provide to the electronic circuitry an electrical signal related to a temperature of the strain sensor and/or a temperature of a region of the substrate adjacent to the strain sensor. the at least one strain sensor (500, 520, 540) comprises a plurality of stretchable tracks (204, 304, 324, 324') positioned on the substrate; the resistance of the at least one strain sensor increases as at least some tracks of the plurality of stretchable tracks are elongated due to the contact layer being elongated; the electronic circuitry is configured to determine an angle and/or a range of movement of the joint responsive to changes in the resistance of the at least one strain sensor (500, 520, 540); wherein the electronic circuitry comprises a machine-readable memory configured to record information related to an elongation of the at least one strain sensor; the electronic circuitry is configured to automatically collect data from the strain sensor at a predetermined frequency; and the apparatus further comprises a temperature sensor, wherein the temperature sensor is configured to provide to the electronic circuitry an electrical signal related to a temperature of the strain sensor and/or a temperature of a region of the substrate adjacent to the strain sensor.