Motivated by the need to incorporate human spine mechanics into the design loop of a wearable spine-assistive device to prevent low back pain, this article presents a novel method to model the spine as a series of pin-connected triangles and reconstruct its shape/curvature in the sagittal plane from the measured back profile along the pathlength between the neck and the pelvis by template matching without relying on the common assumption that the back profile and spine are parallel or medical images to calibrate the subject-specific parameters. The findings verify that the vertebrae of human spines are similar and can be scaled using an anatomically based spine as a template. Formulated as a constrained optimization problem to account for the deformable skin movements and subject-dependent variations [height/weight and subcutaneous fat tissue thickness (SFTT)], the templet-matching method that solves the template-feature positions eliminates common errors caused by tracking the skin markers as the points on the spine curve and is evaluated in two scenarios; both use the same template of an anatomically based spine. The first uses published magnetic resonance imaging (MRI) data of eight subjects’ standing and flexion postures to validate the method. The second illustrates its effectiveness using images captured by a commercial human motion-capturing system experimentally. As verified with X-ray images that serve as ground truth for comparison, the findings demonstrate that the method offers an effective tool to reveal the internal kinematics of the spine from the measured profile of the human back.