We are familiar with our quadriceps muscles – the bulky muscles on the front of the thigh. We readily associated these muscles with extending (straightening) the knee since these muscles come together to form a single tendon that crosses the knee joint. But how the quadriceps attach at the other ends often gets missed with regards to how muscle tension in the thighs can affect the hips and spine.
Looking at the quadriceps in more anatomical depth, we have 4 quadriceps muscles: the vastus lateralis (outer quadriceps), vastus medialis (inner quadriceps), vastus intermedius (middle quadriceps that lies deep), and the rectus fermoris (middle quadriceps that lies superficial to vastus intermedius). As mentioned, all four quadriceps muscles join at the patella (knee cap) via a single tendon and continues via the patellar tendon/ligament to the shin bone (tibial tuberosity). The 3 vastus quadriceps attach on the upper portion of the thigh bone (femur). The rectus fermoris stands out from the other quadriceps since it actually crosses the hip joint and attaches at the hip (anterior inferior iliac spine of the ilium) making it a hip flexor.
When we flex/bend the knee, all 4 quadriceps muscles are taken into expansion with the isolation predominantly being in the 3 vastus muscles. The stretch travels up the rectus femoris creating a ‘pull’ on the hip attachment. If the hip is not stabilized, the hip can be pulled into an anterior forward tilt. This anterior tilt travels into the spine pulling the lumbar vertebrae also forward into an excessive lordotic curve.
This is commonly seen in simple standing quadriceps balancing stretches (standing on one foot and holding the opposite ankle to stretch the thigh). As we line up the knees and thighs parallel to each other, the rectus femoris tension acts on the pelvis. Without stabilizing the pelvis, the pelvis drops forward and placing compression into the lower back.
Understanding this kinetic chain of muscle and joint actions of the rectus femoris, it becomes important in these quadriceps stretches to engage the abdominal muscles. The abdominal muscles function to flex the trunk as well as generate a posterior tilt of the pelvis, which perfectly counters the pull of the rectus femoris.
Whether you are standing, lying on your belly/side, or in pose variations taking a stretch through the quadriceps, continuously feed engagement through the abdominal muscles to neutralize the pelvis. A great visual is to picture the pubic bone and bottom ribs moving closer towards each other (posterior pelvic tilt). Feel the increased isolation of the rectus femoris along with retained spaciousness of the lower back. Keep in mind that with any stretch through the knee that no discomfort should be felt.