This thesis contains work carried out in two separate fields of medical physics. Firstly, an instrument is described which enable orthopaedic surgeons to measure the in vivo sarcomere length in muscle fibre. The technique relies on the diffraction of laser light as it passes through the periodic structure of striated muscle. The resulting instrument is a modification of one described by other workers. Various refinements to the instrument were carried out and tested during several tendon-transfer operations. A precision of 3% in the sarcomere length may be achieved which is adequate for the surgeons needs. Secondly, simulations and experiments were performed to investigate an arcing Total Body Irradiation technique to be used in radiotherapy. The technique was first proposed by workers at Christchurch Hospital and this work continues that study. Computer code was written to simulate the treatment using Monte Carlo methods for radiation transport. Various characteristics of the treatment were examined such as dose rates, dose uniformity and dose compensation. These properties must be known if the treatment is to be implemented in a clinical situation. An anthropomorphic model was used which demonstrates the dose uniformity achievable with this method.