M van Selm

Date of Award


Degree Name

Master of Philosophy (School of Physiotherapy)

Schools and Centres


First Supervisor

Professor Benedict Wand

Second Supervisor

Dr William Gibson


Previous research has suggested that looking at a painful body part has an analgesic effect on experimental pain. Furthermore, it has been demonstrated that magnifying the size of the viewed part has a greater analgesic effect, while minifying the perceived size of the body part reduces the analgesia. These studies involved the application of a noxious stimulus to the skin, inducing pain that is perceived superficially. It is believed that most clinical pain is likely contributed to by noxious information from deep tissues and is certainly more commonly perceived as deep (below the skin surface). Research on clinical populations has also supported the idea that visualisation of the painful body part is analgesic, however the effects of magnification and minification are opposite to those seen with an experimental pain paradigm. While a number of mechanisms might explain these differences it is possible that the modulatory effect of vision is different for pain that is perceived superficially to that which is perceived deeply.

Here we explore the effects of visualisation and visual enlargement on experimental deep tissue pain of the anterior thigh. All participants undertook a bout of high load eccentric exercise to induce delayed onset muscle soreness. Twenty four hours later those participants who reported at least a moderate level of muscle soreness were tested in a four phase randomised cross-over experiment. We measured pain intensity during the performance of a standardised quadriceps contraction under four different visual conditions, namely: normal visualisation of the thigh; magnified visualisation of the thigh; visualisation of the contralateral uninjured thigh and visualisation of a neutral object. Contrary to previous research on superficially perceived pain, we found no difference in pain intensity across any of the four conditions. These results demonstrate that visualisation does not have an analgesic effect on experimental deep tissue pain, suggesting that different modulatory factors exist for superficial and deep experimental pain. It also proposes the notion that visualisation may only have a modulatory effect on experimental pain when visual feedback offers a significant contribution to the perception of safety of the stimulated structure. Visualisation provides clear information that all is well with the skin but less credible evidence that all is well with deep structures, however this hypothesis remains to be tested.