Abstract Orakifar N, Kamali F, Pirouzi S, Jamshidi F. Sacroiliac joint manipulation attenuates alpha-motoneuron activity in healthy women: a quasi-experimental study. Objective To determine whether sacroiliac joint (SIJ) manipulation decreases α-motoneuron activity and increases the pressure pain threshold (PPT) over the posterior superior iliac spine (PSIS) in healthy women. Design Quasi-experimental study. Setting A university medical center. Participants Healthy young women (N=20) aged 18 to 30 years were recruited from among the students of a university medical center after a request for volunteers. Interventions Joint manipulation consisted of the supine rotational glide manipulation for the sacroiliac region. PPT measurements from the PSIS and Hoffman-reflex (H-reflex) amplitudes from the tibial nerve on the same side were recorded before and after joint manipulation. PPT was monitored for 15 minutes and H-reflex for 20 minutes after the procedure. Main Outcome Measures Changes in tibial nerve H-reflex amplitude and PPT values after SIJ manipulation. Results SIJ manipulation attenuated α-motoneuronal activity significantly ( P<.05) but transiently, since the decrease was seen only for 20 seconds after the intervention. There was no positive significant difference in the PPT after SIJ manipulation at any time during postintervention follow-up. Conclusions SIJ manipulation produced a transient attenuation of α-motoneuron excitability in healthy women. These findings demonstrate that our manipulation technique can lead to a short-term reduction in muscle tone as a result of changes in sensory discharge, predominantly in la afferents. SIJ manipulation did not significantly affect the PPT in healthy women.