This interesting paper demonstrates the application of biomechanical simulation techniques to the human-centered design of rehabilitation devices. It uses models of the behavior of the upper body and alternative designs of a passive exoskeleton to optimize the choice of components of the exoskeleton, in particular the choice of spring stiffness within the mechanism. The aim of the exoskeleton is to enable a patient with a brachial plexus injury to carry out activities of daily life, such as lifting a cup to drink when seated, without exceeding his or her pain threshold. Such injuries are sustained in road traffic accidents and leave some muscles weak. This is a major issue for patients, and understanding how to model and manage such weak muscle injuries meaningfully is a major issue within the design of assistive devices.

The key contribution of the paper is to show, via this specific example, an important general approach where the models developed are validated by the construction of prototypes. Reading the paper raises a number of fundamental areas for further work, particularly the effects of variation between individuals and how modeling muscle strength recovery would be addressed.