What do your hamstrings have to do with your core? Or your toes for that matter?
When people talk about the hamstrings, they're usually referring to a group of three muscles that begin at the bottom of the pelvis and extend across the back of the thigh, cross the knee and end on either side of the leg at the top of the calf. Technically, the hamstrings are the five tendons that these three muscles - the semitendenosus, semimembranosus and the biceps femoris - attach to and pull to create flexion of the knee and extension of the hip.
In order to stretch or strengthen any muscle, though, the ends of it have to be anchored for intentional movement. The anchor at the end of the muscles closest to the head is the pelvis and our connection to the pelvis is deepest when we engage the pelvic floor, the foundation of the core. The pelvic floor margins integrate with the transverse abdominus and the complex make up what yoga folks call "mula bandha" or "root lock.
When you revolve the body with attention and intention you necessarily engage not only the deep core but also the obliques, the diagonal muscles wrapping from the ribs to the pelvis. Caution: many people in revolved poses (twists) do not sense and engage these muscles fully and this can lead to injury. Attention and intention.
Why the toes? In the case of the hamstrings, you're working with muscles that not only cross a joint (the knee), but integrate with the muscles further from the head through deep fascial connections. The hamstrings are part of the Superficial Back Line (<-That link goes to a video of the dissected structures from a cadaver, just so you know what you're getting into. It's not bloody, but is a dead human.) Through fascial connections, the hamstrings are part of a continuous set of tissue running from the bottom of the feet and base of the toes, up the back of each leg, under the glutes to join over the sacrum and continues alongside either side of the spine, neck and over the head to the brow ridge. Yes, from head to toe, quite literally. This means that if you don't anchor the distal end - the end away from the head by flexing the foot, you don't occupy the pose or the muscle fully.
Every muscle of the body is part of a line like this, a connected continuum forming the mobile structure of the body. This is one of the reasons yoga is unique as a form of exercise: we strive to bring awareness - attention and intention - to every muscle, fiber and cell of the body in every pose. No part of the body goes into Savasana (Final Resting Pose) until they all do at the end, and this, too, is done intentionally. The integration is complete.
This week we explore the integration from sitting bone to sole of foot through the hamstring muscle complex. Regardless of what else in the world you occupy, occupy your body first!