A capacitive sensor device, including electrode materials carried by fabric substrates, is provided for monitoring relative movement of an expanding and/or contracting structure, such as the mammalian chest and/or torso, corresponding to a performance parameter related, for example, to respiratory function. Some embodiments include non-woven fabric substrates comprising compliant portions configured to stretch only in a selected direction and non-compliant portions upon which electrode materials are disposed. In some embodiments, layers of fabric substrates, carrying corresponding first and second electrode materials, are configured to cooperate to form a parallel plate capacitive sensor having a variable capacitance corresponding to a relative motion of the fabric substrates.