Submitted in partial compliance with the requirements for the Master’s Degree in Technology: Chiropractic, Department of Chiropractic, Durban University of Technology, Durban, South Africa, 2015. / Background: Spinal manipulative therapy (SMT) is a commonly used treatment for many musculoskeletal conditions although the exact mechanism explaining its effectiveness is not well understood. Several studies have investigated the effect of SMT on the paraspinal muscles where neuromuscular effects have been observed, however few studies have assessed whether these changes result in a change in the functioning of the paraspinal muscles. This study aimed to determine the effect of lower thoracic spinal manipulation compared to a placebo intervention on lumbar extensor muscle endurance in asymptomatic participants. Methodology: This was a quantitative, pre-test post-test, placebo controlled trial involving 40 male participants between the ages of 20 and 40 years. The participants were randomly allocated to either the lower thoracic spinal manipulation group or a placebo group. Manipulation was delivered using the Impulse Adjusting Instrument®. Objective measures included lumbar spinal range of motion, a paraspinal muscle endurance test, and surface electromyography readings. Subjective measures were the verbalisation of pain and/or discomfort during the paraspinal muscle endurance test. IBM® SPSS® statistics version 21 and STATA 11 were used to analyse the data. A p-value of <0.05 was considered statistically significant. Results: There were no statistically significant differences between the groups in terms of subjective and objective measurements. A trend of treatment effect was observed for paraspinal muscle endurance where the intervention group showed noticeable improvements in endurance scores. Conclusion: Further studies need to be conducted to determine if the trends observed would occur in a larger study population.