Body Posture & Muscles Functions: (Part 6)

In this post, I will start off with brief explanation about back extensors' test. Once we are done reviewing the test, I will discuss about the simple tests for glutes and QLO. This back extensor test, can be apply to general population and even professional athletes.

In the trunk extension test for the back extensors, the erector spinae muscles are assisted by the latissimus dorsi, quadratus lumborum, and trapezius. In the prone position, the low back will assume a normal anterior curve. To avoid false interpretations of the test results, it may be necessary to perform some preliminary tests. It is not necessary to do so routinely, however, because close observation of the subject in a prone position and of the movements taking place during trunk extension will indicate if preliminary tests for length of hip flexors and strength of the hip extensors are needed. Now, let me present to you the back extensor test. 

Patient: Prone, with hands clasped behind the buttocks (or behind the head).

Fixation: Hip extensors must give fixation of the pelvis to the thighs. The examiner stabilizes the legs firmly on the table.

Test Movement: Trunk extension to the subject's full range of motion.

Resistance: Gravity. Hands behind the head, or hands behind the lower back.

Grading: The ability to complete the movement and hold the position with hands behind the head or behind the back may be considered as normal strength. The low back muscles are seldom weak, but if there appears to be weakness, then hip flexor tightness and/or hip extensor weakness must be ruled out first. Actual weakness can usually be determined by having the examiner raise the subject's trunk in extension (to the subject's maximum range) and then asking the subject to hold the completed test position. Inability to hold this position will indicate weakness. Weakness is best described as slight, moderate, or marked based on the judgment of the examiner.

If the hip extensors are weak, it is possible that the examiner can stabilize the pelvis firmly in the direction of posterior tilt toward the thighs, provided that the legs are also firmly held down by another person or by straps. Alternatively, the subject may be placed at the end of the table, with the trunk in a prone position and legs hanging down with knees bent as needed. The examiner then stabilizes the pelvis and asks subject to raise the trunk in extension and hold it against pressure. In the presence of tight hip flexors, the back will assume a degree of extension (e.g lordosis) commensurate with the amount of hip flexor tightness. In other words, the low back will be in extension before beginning the trunk extension movement. In such a case, the subject will be limited in the height to which the trunk can be raised, and the mistaken interpretation may be that the back muscles are weak.

A similar situation may arise if the hip extensor muscles are weak. For strong extension of the back, the hip extensors must stabilize the pelvis toward the thighs. If the hip extensors cannot provide this stabilization, the pelvis will be pulled upward by the back extensors into a position of back extension. Again, as in the case of hip flexor tightness, if the back is already in some extension before the trunk-raising movement is started, the trunk will not be raised as high off the table as it would be if the pelvis were fixed in extension on the thighs.

Gluteus Maximus (How weak is your glutes?)

Lying prone on a table, this subject exhibits a normal anterior curve in the

lower back

The moment that back extension is initiated, the curve in the lower back increases

because of weakness in the gluteus maximus.

When extension is continued, the subject can raise the trunk higher, but not to

completion of the range of motion.

Holding the pelvis in the direction of posterior pelvic tilt, in the manner provided

by a strong gluteus maximus, enables the subject to complete the full

range of motion.

We've covered back extensors and glutes tests. Now, let's move on to a quick test on the quadratus lumborum. The quadratus lumborum acts with other muscles in lateral trunk flexion. It is difficult to palpate this muscle because it lies deep beneath the erector spinae. Although the quadratus lumborum enters into the motion of elevation of the pelvis in the standing position or in walking, the standing position does not offer a satisfactory position for testing. Elevation of the right side of the pelvis in standing, for example, depends as much (if not more) on the downward pull by the abductors of the left hip joint as it does on the upward pull of the right lateral abdominals.

Quadratus Lumborum (QLO)

Origin: Iliolumbar ligament, iliac crest. Occasionally from upper borders of the transverse processes of the lower three or four lumbar vertebrae. 

Insertion: Inferior border of the last rib and transverse processes of the upper four lumbar vertebrae.

Action: Assists in extension, laterally flexes the lumbar vertebral column, and depresses the last rib. Bilaterally, when acting together with the diaphragm, fixes the last two ribs during respiration.

Nerve: Lumbar plexus, T12, LI, 2, 3.

Patient: Prone.

Fixation: By muscles that hold the femur firmly in the

acetabulum.

Test Movement: Lateral elevation of the pelvis. The extremity is placed in slight extension and in the degree of abduction that corresponds with the line of fibers of the quadratus lumborum.

Resistance: Given in the form of traction on the extremity, directly opposing the line of pull of the quadratus lumborum. If the hip muscles are weak, pressure may be given against the posterolateral iliac crest opposite the line of pull of the muscle.

Grading: Grading the strength of this muscle numerically is not recommended. Simply record whether it appears to be weak or strong.

The coming weeks will be very busy on my schedule, stay tuned as I will try to finish off a couple more posts on this discussion.