Background: Paradoxically, despite its demonstrated efficacy in the short term (4 weeks) management of pain of cervical origin and its wide spread clinical acceptance by healthcare practitioners, there is relatively scant evidence about the effects of manual therapy and its underlying mechanisms of action. Recent meta-analyses of clinical trials of manual therapy have identified mobilisation therapy rather than manipulation as the physical treatment of choice for neck pain. Manual therapy effects are usually studied under biomechanical, biophysical I psycho-physiological and psychological paradigms. Cervical mobilisation therapy has attracted least attention.
Pain is a key clinical feature for which mobilisation therapy is indicated. The midbrain periaqueductal gray not only plays a significant roie in endogenous pain control but also in the integration of sensory, motor and sympathetic responses to a range of stimuli. The periaqueductal gray consists of a number of functionally distinct columns that have historically been delineated by the pattern of sympathetic nervous system responses evoked from its stimulation. For example, stimulation of the lateral column produces sympathoexcitatory effects that occur in concert with analgesia whereas the ventrolateral column produces concurrent sympathoinhibition and analgesia. This coordinating role of the periaqueductal gray occurs through relays in diverse pontomedullary structures that are responsible for isolated control of a variety of sympathetic nervous system functions and pain. The question that arose from this knowledge was: do parallels exist between the effect response profile of manual therapy and stimulation of the periaqueductal gray? This question was answered in two parts. The first involved the study of manual therapy effects on the sympathetic nervous system and pain (chapters 7 and 8 ) . The second evaluated the relationship between manual therapy induced changes in sympathetic nervous system function and pain (chapter 9).
Method: This thesis consists of a series of seven, randomized, double blind, placebo controlled, within-subjects studies (chapters 7, 8 and 9) in which asymptomatic and symptomatic (lateral epicondylalgia, chapter 4) subjects were investigated under similar experimental conditions (chapter 5). The dependent variables were a lateral glide treatment technique (ie, a lateral displacement between C5 and T1, oscillating frequency of about 1.3 Hz, chapter 6), a placebo condition and a control condition. Indicators of sympathetic nervous system function (ie, skin conductance, skin temperature, skin blood flux, blood pressure, heart rate and respiratory rate) and hypoalgesia (ie, mechanical and thermal pain threshold tests, neurodynamic tests, painfree grip strength test) were the independent variables.
Results: The lateral glide treatment technique, when compared against the placebo and control conditions, consistently produced an initial sympathoexcitatory effect and an initial hypoalgesic effect (chapters 7 to 9). Confirmatory Factor Analysis modeling validated the interpretation of changes in the dependent variables as either being related to a sympathoexcitatory effect (ie, the latent factor for the observed variables: skin conductance, skin temperature and cutaneous blood flux) or an hypoalgesic effect (ie, the latent factor for the observed variables: pressure pain threshold, neurodynamic tests, painfree grip test). More importantly, confirmatory factor analysis demonstrated a robust relationship between the latent factors of sympathoexcitation and hypoalgesia (chapter 9).......................................................