Anatomy Lesson

For months, I've been calling the muscles that seem to always get stiff and sore after a tougher running workout the "hip flexors."  While resting yesterday from Friday's long run, I did a lot of stretching and self-massage, concentrating on those muscles in the hip/groin area; and I started to wonder if I was identifying them correctly.  The band of muscle that was most tender seemed to extend down to the knee, though the point of soreness was only at the upper end, in the front hip region.  Wouldn't that be a quadricep? 

The hip flexors are a group up muscles that serve to lift the knee forward and upward, "flexing the femur onto the lumbo-pelvic region."  The quadriceps are a set of four muscles that act to extend the the leg at the knee...oh, and hey, one portion also assists in lifting the knee.

When I think of the quads, I think of the obvious large-belly muscles that can be seen when the leg flexes under compression of weight or when under the strain of pressing the legs to extend when weighted.  In weight training, I'll work them with the leg extension and leg press machines. They're most evident when I'm sitting and I extend the knee.  The vastus lateralis bulges on the outside, from above the knee up the side of the thigh; the vastus medialis bulges on the inside of the thigh, lower and closer to the knee; and (what I thought was) the vastus intermedius pops up between them and fades into the upper thigh near the hip. 

But wait: that's only three.  "Quad" means four.  There's also the rectus femoris.  It's the only one of the four quads that connect to the hip, so it assists in hip flexion.  Turns out, that muscle in the middle of the thigh IS the rectus femoris and not the vastus intermedius.  The vastus intermedius lies deeper in the leg and is covered by the rectus femoris. 

When I sit in a chair and flex my leg at the knee, I can feel the region that is most often sore, and it's up at the top section of that rectus femoris.  In fact, massage down the length of that muscle along the thigh towards the knee reveals that that very well could be the muscle that I should be addressing, and not the hip flexors in particular.

Hip flexor weakness could be a reason for the added strain that the rectus femoris is experiencing, since they work together to flex the leg forward and upward at the hip.

When I'm going through that DOM period when the muscles are at their most sore, I can stand and flex the knee with no discomfort and I can lift the knee upward while keeping the knee bent with no problem.  But if I bring the leg forward without bending the knee, I can feel it.   If I lift the knee and then try to extend the lower leg at the knee, I can feel it.  If I sit and extend the leg at the knee while the thigh is supported on the chair, it's easy.  If I sit and extend the knee, but lift the thigh a little so the hip flexors have to work to support it, I can feel the soreness high on the thigh and in the hips. 

So, it isn't simply hip flexors that are troublesome. It's quadriceps too.  I wouldn't call this "injury" either.  I think it's a natural process of adaptation to stress that goes into building the muscles.  But what I think is happening is that my quads are strengthening (and complaining during the process) while the hip flexors are trying to get a free ride.  They need to pull their weight (literally), which should help take the strain off the rectus femoris.