Is the psoas a hip flexor in the active straight leg raise?

Abstract

Psoas function is a topic of considerable relevance in sports and clinical science. However, the literature on psoas function is not sufficiently consistent. Questions are, amongst others, if during hip flexion the psoas always has the same function as the iliacus, and if the psoas affects the hip more than the lumbar spine. In the present study, 17 healthy women, 20–40 years, performed the active straight leg raise (ASLR), with the right or the left leg (“Side”), and without or with weight added above the ankle (“Condition”). Electromyographic (EMG) activity of psoas and iliacus were recorded with fine-wire electrodes, and of rectus femoris and adductor longus with surface electrodes, all on the right side. Movements of the leg were recorded with active markers and a camera system. During ASLR, the iliacus, rectus femoris, adductor longus and psoas were active ipsilaterally, but psoas was also active contralaterally. All muscles started to contract before movement onset, the iliacus, rectus femoris, and adductor longus largely at the same time, before the psoas. There was no significant difference between the amplitude or time of onset of ipsilateral and contralateral psoas EMG activity, nor was there a significant interaction between Side and Condition for the psoas. Although ipsilateral psoas activity is consistent with the psoas being a hip flexor, contralateral activity is not. The most simplest explanation of the pattern found is that the psoas is bilaterally recruited to stabilize the lumbar spine, probably in the frontal plane.

Comparison of Mini-squats and Straight Leg Raises in Patients with Knee Osteoarthritis: A Randomized Controlled Clinical Trial

“…Moreover, three muscles began to contract even before the psoas muscle. [32] Because of the bi-articular structure of the rectus femoris part of the quadriceps muscle, we preferred straight leg raises.…”

Comparison of psoas major muscle thickness measured by sonography during active straight leg raising in subjects with and without uncontrolled lumbopelvic rotation

“…ASLR is involved with hip flexion, and associated with lumbar stability (Yoshio et al, 2002;Hu et al, 2011). Therefore, investigation of the cPM activity during ASLR is clinically relevant for evaluating lumbopelvic stability.…”

“…Hu et al (2011) stated that during active straight leg-raising (ASLR), various muscles are active, including the iliacus, rectus femoris, and ipsilateral PM (iPM); the contralateral PM (cPM) is also active. In addition, most authors agree that PM activity increases with greater hip flexion, while Yoshio et al (2002) even concluded that the PM mainly works as a stabilizer of the lumbar spine and the femoral head over the first 15 of hip flexion, and does not become an effective hip flexor prior to 45 of flexion (Yoshio et al, 2002;Hu et al, 2011).…”

“…Recent studies have shown that the psoas major (PM) contributes to stabilization of the lumbar spine (LS) (Santaguida and McGill, 1995;Yoshio et al, 2002;Hu et al, 2011). Hu et al (2011) stated that during active straight leg-raising (ASLR), various muscles are active, including the iliacus, rectus femoris, and ipsilateral PM (iPM); the contralateral PM (cPM) is also active.…”

“…Active straight leg raising involves both hip flexion and LS stability because gravity has a large moment and affects muscle contraction (Hu et al, 2010(Hu et al, , 2011. The PM in particular is considered a lateral stabilizer of the LS (Santaguida and McGill, 1995).…”