From my clinical experiences thus far, I have found that many individuals with low back pain lack proper gluteus maximus strength. (This should not be a surprise to you unless you went to physical therapy school when dinosaurs were still roaming). I often find that the gluteals are weak due to a combination of disuse atrophy and muscle inhibition secondary to pain. In the case of disuse atrophy, the individual does not activate their gluts and therefore preferentially activates other muscles to perform the movement. For example, think about the individual who arches his/her back to pick up a box rather than perform a hip hinge and squat OR consider the individual who rests in lumbar extension, locking out the lumbar facets and resting on the anterior hip ligaments. They avoid the gluteals and activate their lumbar paraspinals and hamstrings to perform movements. With pain inhibition, the gluteals are not receiving proper neuromuscular facilitation because pain is overriding the movement. The muscles are temporarily unable to fire because pain is inhibiting the activation. In either situation, properly assessing hip strength and assessing the cause of weakness is a fundamental part of a low back evaluation.
In this post, I want to discuss hamstring dominance is relation to gluteus maximus testing. As I stated in the previous paragraph, poor movement patterns often lead to improper activation of the glut muscles. Since the gluts are not helping perform the movement, a different muscle overcompensates to perform the movement. Clinically, I often find that this other muscle is the hamstrings (or lumbar paraspinals). Individuals that preferentially activate their hamstrings prior to their gluts are called 'hamstring dominant.' This can be problematic because the gluteals are meant to act as a hip stabilizer and extensor. When they do not fire first, the gluteals do not stablize. The hamstrings attempt to act as both a prime mover and stabilizer.
The test for hamstring dominance is similar to the Kendall Glut Max testing position. Place the individual in prone with the tested knee bent to 90 degrees. Ask them to lift their leg off the table. In the normal healthy individual, the glut max engages prior to the hamstrings. Proper activation order: 1. TrA engages, 2. gluteus maximus activates, 3. hamstrings fire as the leg is lifted. If the hamstrings fire before the glut max, the individual drives that motion with the hamstrings.
In the video below, the individual presents with both hamstring and lumbar paraspinal dominance over gluteal muscle activation. He compensates by arching through his low back and avoids using his glutes.
(Video feed has been taken from The Movement Corner on the OPTIM Manual Therapy Felowship Website)
Do not be fooled by strong gluts in the low back pain population. After assessing the glut max, retest for hamstring dominance to ensure they are not over-activating the hamstrings. I frequently discuss dominance patterns on The Movement Corner as they are common causes of movement dysfunction. I highly recommend assessing for hamstring dominance in your lumbar patients.
-Jim Heafner PT, DPT, OCS