Introduction: This study aimed to compare the immediate effects of Posterior Anterior (PA) L4 and L5 mobilisations on range of motion and muscle activity measures in the lumbar and hamstring regions of asymptomatic individuals. Methods: Thirty-eight participants were randomly allocated to a mobilisation (n=20) or control (n=18) group. The mobilisation group received central PA mobilisations to the L4 and L5 vertebrae, three times for two minutes. The control group received no mobilisation. Pre- and post-test measures included lumbar range of motion, measured by the modified Schober test and hamstring extensibility by the active knee extension test. Local Erector Spinae and Biceps Femoris muscle activation were also measured by surface Electromyography. Data were analysed using magnitude-based inferences. Results: Lumbar mobilisations had a most likely beneficial effect on active lumbar flexion 18.6% (90% CL 11.8% ± 25.8%) and active knee extension range 22.8% (-29.6% ± 15.2%). Mobilisations had a possible beneficial effect in sEMG activation reduction of the Erector Spinae -4.7% (-10.5% ± 1.4%) and Bicep Femoris -6.1% (-13.1% ± 1.6%) during lumbar flexion. Likely beneficial effects of reduced sEMG were found following mobilisations during the active knee extension test for the Erector Spinae -18.3% (-27.7% – 7.6%) and Biceps Femoris muscle activity -20.8% (-30.9% ± 9.2%). Discussion: L4 and L5 mobilisations increase lumbar and hamstring range of motion in the immediate term. Our unique finding was that, in this sample population, muscle activity in both local Erector Spinae and Biceps Femoris reduced, most likely due to the mobilisations applied.