Leg Raises, Sit-Ups, and Core Exercise That Lock Your Feet Down
By Brent Brookbush MS, PES, CES, CSCS, ACSM H/FS
This is one of the few examples in our questionable exercise list that does not require more thanthe optimal range of motion (ROM) at any joint. However, these exercises are some of the most problematic. One version of the leg raise is actually at the very top of my list and will be discussed in more detail later in this article.
These exercises have a propensity to strengthen short/hypertonic structures (contributing to postural dysfunction), and stress passive structures (supporting structures of the lumbar spine) increasing the risk of chronic and acute injury.
Studies have reported those exercises that involve leg movement and those that lock the feet into position increase the activity of hip flexor musculature (Iliopsoas, TFL, rectus
femoris, and pectineus) and decrease the activity of abdominal musculature. The percentage of individuals who enter the gym with low back pain and/or an anterior pelvic tilt (APT) is more than 85%. The cause of these issues may be linked to limited hip and lumbar spine flexibility – often attributed to a tight/over-active psoas, lumbar extensors, and quadratus lumborum.
When we examine our three most prevalent postural dysfunctions – all indicate one or more of the hip flexors as tight and over-active.
Upper-Body Dysfunction:
Psoas is short/overactive: The psoas becomes synergistically dominant to stabilize the
spine due to the inhibition of the intrinsic stabilization subsystem (TVA, pelvic floor, diaphragm, and intrinsic muscles of the spine) by over-activity in the lats and rectus abdominis.
Lumbo-Pelvic Hip Dysfunction:
Psoas is short/overactive: The psoas is “stuck” in a shortened position in an anterior
pelvic tilt (APT) both as a hip flexor and lumbar extensor. If postural dysfunction becomes chronic the psoas will adaptively shorten, develop trigger points and become hypertonic (sometimes referred to as psoas “contractures”). It is often insinuated as the primary culprit for this compensation pattern. It should be noted that in an APT all hip-flexors may adaptively shorten to accommodate the compensatory length change.
Lower-Leg Dysfunction:
TFL is short/overactive: Lower leg dysfunction includes shortening and hyperactivity of the TFL as an external rotator of the tibia (via the iliotibial band), but the TFL is also a hip flexor. It is not uncommon for an individual with lower-leg dysfunction to develop an anterior pelvic tilt setting the stage for adaptive shortening by other hip flexors.
When we apply our knowledge of postural dysfunction and length/tension relationships; the hip-flexors would likely benefit most from flexibility techniques. Practice has shown that flexibility alone will often address any “weakness” noted in these muscles as they are returned to their optimal length. Strengthening of the hip-flexor musculature will often exacerbate dysfunction and lead to further deviations from optimal flexibility. All of the exercises indicated in the title of this article are primarily hip flexion. Despite the recruitment of core musculature, the stress placed on the hip-flexors often counters any positive benefit we could gain from these exercise selections. Bridges, planks, side planks, crunches, prone cobras, and chops are all examples of core strengthening exercise that do not rely on the hip flexor musculature as the primary mover or stabilizer.
Hip flexor exercise may also place undue stress on the supporting tissues of the lumbar spine. This is most easily visualized in my least favorite of all exercises – “the ballistic straight-leg throw-down and raise.” In this exercise (as well as many of the other exercises listed) the psoas must generate incredible amounts of force to eccentrically decelerate and concentrically accelerate the mass of the legs. When the psoas generates force, the force is transmitted to both the femur and lumbar spine in equal proportion (origin and insertion). Unfortunately the vectors of force generated by the psoas on the lumbar spine also creates an anterior shear force. Unlike the joints of the hip and thoracic spine the lumbar spine does not have sufficient musculature and/or the bony support to counteract this anterior shear force (create a posterior force). The only musculature capable of
generating a counteracting force is increased intra-abdominal pressure via our intrinsic stabilization subsystem (drawing in, and bracing if necessary).
In the example of the “ballistic straight leg raise” it is simply not possible for enough intra-abdominal pressure to be generated to compensate for this force (part of this is due to the diffuse force created
by increased intra-abdominal pressure versus the fairly acute force created by the psoas). When the intrinsic stabilization subsystem fails to create an equal posterior force we note an increase in lumbar extension and abdominal distension. At this point, it is fair to assume that passive structures (anterior longitudinal ligament, posterior longitudinal ligament, capsules of the zygapophysial joints, and the intervertebral disks) are “absorbing” the difference between the anterior and posterior forces.
© Brent Brookbush 2011
Questions, comments, and criticisms are welcomed and encouraged –