Prone hip extension test – 30 degrees hip abduction or neutral that is the question?

Activation of the gluteus maximus (GM) and hamstring muscles during withprone hip extension with knee flexion (PHEKF) in three hip abduction positions was explored by researchers Sun-Young Kang, Hye-Seon Jeon, Ohyun Kwon, Heon-seock Cynn, Boram Choi.  They concluded that to facilitate the activation of GM in PHEKF it should be performed in 30° abduction and their results were published in in Manual Therapy 2013: 18, 4, 303–307.   Kinetic Control Accredited Tutors Danielle Debbrecht and Patrik Pedersen have something to say about this.

Study summary

In a 2013 study, Kang et al looked at the influence of hip abduction on activation patterns of Gluteus Maximus (GM) and Hamstrings (HAM) in prone hip extension with knee flexion (PHEKF).  The study was conducted on 30 young healthy subjects, with no history of lumbar, sacroiliac or lower limb injury within the past two years.  Surface EMG signals were recorded from the GM and the HAM, during PHEKF in 0°, 15° and 30° of hip abduction.  Results indicate the greatest GM EMG amplitude at 30° hip abduction followed by 15° hip abduction and the lowest amplitude at 0° abduction.  For HAM the EMG amplitude  was greatest at 0° of abduction and no difference was seen between 15° and 30° of abduction.  Further it was shown that the relative EMG onset of GM and HAM differed depending on the abduction angle. In 0° of abduction HAM fired earlier than GM, but in both 15° and 30° of abduction the pattern was reversed and HAM was delayed compared to GM.  The conclusion drawn was that to facilitate the activation of GM in PHEKF, it should be performed in 30° abduction.

Review and recommendations

After reading this article, 2 primary considerations come to mind regarding the interpretation of this research and its effectiveness in clinical practice.

1) During EMG studies, positions that combine multiple muscle functions will get the greatest EMG amplitude.  GM has a broad muscle attachment allowing it to impact hip extension, abduction, lateral rotation.  GM has both a stabilizer and mobilizer role.  The most superficial and lateral GM fibers where surface EMG was recorded in this study comprise the mobilizer portion of GM.  These fibers are best suited for producing high force hip abduction and lateral rotation movements like those required during cutting maneuvers in sport.  In contrast, the more medial fibers of the GM function as a hip and lumbar spine stabilizer to decelerate forces during sagital plane function.  So, rather than focus on the position of highest EMG amplitude, our pain population is best served by restoring sagital plane GM control during functional activities to prevent dominance of hamstrings and erector spinae muscle groups.  Thus restoring recruitment dominance between synergists is far more critical in the rehabilitation setting than maximizing the amplitude of GM firing.

2)  It’s not surprising that in the position of 0° of abduction that the HAM fired before GM.  First, the HAM are a sagittal plane mobilizer often dominant to the stabilizer GM synergist in individuals with pain and those at risk for pain.  When faced with a task of lifting the thigh off the table, the brain has a few options.  The easier option for many, especially those with a history of hip or lumbar pain, is to extend the knee thus allowing the HAM to shorten at the other end to produce hip extension.  However, when asked to perform the same leg lift with the knee bent, the brain must select another movement option as the HAM is insufficient at shortening at both ends.  Thus, the early firing of the HAM in the 0° hip abduction position could in fact be the brains way of preventing knee extension to complete the desired leg lift with a bent knee.  It’s unclear from the paper what cueing was provided to participants if any or if proximal lumbar control was maintained.  Furthermore, it appears only 3 reps of training were provided prior to EMG testing.  These variances could have impacted GM recruitment timing during testing.  Additionally, in hip abduction (frontal plane) the HAM would be disadvantaged at producing hip extension.  As previously established the GM mobilizer fibers demonstrate the highest EMG amplitude in the abducted position so it’s not surprising that GM fired before HAM in the abducted positions.  However, the delay in HAM firing seen in an abducted hip position doesn’t mean we should train the mobilizer fibers of GM (via exercises in hip abduction) over the GM stabilizer fibers that are biased in neutral hip extension.  Rather, we must restore function of the GM stabilizer fibers to decelerate sagital plane hip and spine movements over the sagital plane mobilizer synergists, hamstrings and erector spinae respectively.

About the authors

Danielle Debbrecht and Patrik Pedersen  are Kinetic Control Accredited Tutors and are always exploring the synergistic actions of muscles and how to get the best out of the global stability muscles. Their course programmes can be seen here.

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