An apparatus for use in estimating the shape of a body part of a subject, which apparatus comprises: a string of sensors for positioning adjacent the body part so that the string of sensors substantially conforms with the shape of the body part, or at least a part of it, the string of sensors comprising: (a) at least one bend sensor having an electrical resistance that changes with bending, the at least one bend sensor being either: (i) a plurality of separate and distinct bend sensors arranged end to end; or (ii) one or a few bend sensors divided lengthwise into different sensing portions to provide an effect similar to the plurality of separate and distinct bend sensors; the length of each bend sensor or each sensing portion such that it bends approximately into a circular arc when positioned on the body part, but not so long that each bend sensor or sensing portion adopts a non-circular shape when conforming to the shape of the body part and not so short that the bend sensor or sensing portion is too stiff to conform to the shape of the body part; and (b) a single stretch sensor for joining the ends of the at least one bend sensor together; the arrangement being such that, in use, the at least one bend sensor lies adjacent a first region of the body part and the single stretch sensor lies adjacent a second region of the body part, wherein the magnitude of a curvature of the first region of the body part is greater than the magnitude of a curvature of the second region of the body part. a string of sensors for positioning adjacent the body part so that the string of sensors substantially conforms with the shape of the body part, or at least a part of it, the string of sensors comprising: (a) at least one bend sensor having an electrical resistance that changes with bending, the at least one bend sensor being either: (i) a plurality of separate and distinct bend sensors arranged end to end; or (ii) one or a few bend sensors divided lengthwise into different sensing portions to provide an effect similar to the plurality of separate and distinct bend sensors; the length of each bend sensor or each sensing portion such that it bends approximately into a circular arc when positioned on the body part, but not so long that each bend sensor or sensing portion adopts a non-circular shape when conforming to the shape of the body part and not so short that the bend sensor or sensing portion is too stiff to conform to the shape of the body part; and (b) a single stretch sensor for joining the ends of the at least one bend sensor together; (a) at least one bend sensor having an electrical resistance that changes with bending, the at least one bend sensor being either: (i) a plurality of separate and distinct bend sensors arranged end to end; or (ii) one or a few bend sensors divided lengthwise into different sensing portions to provide an effect similar to the plurality of separate and distinct bend sensors; the length of each bend sensor or each sensing portion such that it bends approximately into a circular arc when positioned on the body part, but not so long that each bend sensor or sensing portion adopts a non-circular shape when conforming to the shape of the body part and not so short that the bend sensor or sensing portion is too stiff to conform to the shape of the body part; and (i) a plurality of separate and distinct bend sensors arranged end to end; or (ii) one or a few bend sensors divided lengthwise into different sensing portions to provide an effect similar to the plurality of separate and distinct bend sensors; (b) a single stretch sensor for joining the ends of the at least one bend sensor together; the arrangement being such that, in use, the at least one bend sensor lies adjacent a first region of the body part and the single stretch sensor lies adjacent a second region of the body part, wherein the magnitude of a curvature of the first region of the body part is greater than the magnitude of a curvature of the second region of the body part.