Submitted in partial compliance with the requirements for the Masters’ Degree in Technology: Chiropractic, Department of Chiropractic, Durban University of Technology, Durban, South Africa, 2014. / Background: Spinal manipulation has been shown to result in neurophysiological changes, most often noted in the paraspinal muscles. These effects have been associated with an increase in paraspinal muscle contractibility; it is unclear if this leads to an increase in paraspinal muscle endurance. Objectives: To determine the effect of sacroiliac joint (SIJ) manipulation compared to a placebo treatment of the SIJ on lumbar extensor muscle endurance time. Method: A randomised, placebo-controlled pre-test post-test experimental trial, involving 40 asymptomatic male participants divided into an intervention group receiving SIJ manipulation using an impulse adjusting instrument and a placebo group receiving a pre-load force without the delivery of an impulse thrust. Outcome measures were lumbar extensor muscle endurance time, surface electromyographic (SEMG) readings, lumbar spinal range of motion, paraspinal muscle length assessment and a subjective pain measurement. Results: There was a significant difference between the groups (p=0.004) with the SIJ manipulation group showing an increase in endurance time compared to the placebo group which showed a decrease. SEMG readings increased for both groups with no statistically significant difference between the groups (p>0.05). Only extension lumbar spinal range of motion significantly improved in both groups (p=˂0.001) with no significant differences between groups (p=0.876). Only one participant reported pain during the research procedure. Conclusions: SIJ manipulation may enhance the endurance of the paraspinal muscles. This study should be conducted in a larger sample to validate the findings.