Q: I decided it was finally time for me to attempt to integrate more of my core muscles into freestyle rather than simply trying to pull my way through practice. When I was attempting to integrate my core more, I was essentially using my hand as a lever against which to snap my torso, thereby bringing the pulling arm back and extending the other arm, is this the right idea or is there something else I should be going for?
A: Since the water doesn't offer very good traction, it's a bit difficult to use your grip on it—the hand's not a very large gripping surface either—to "snap" something as "massive" (i.e. a significant piece of body mass) as your torso.
It's really not like what occurs when you use your planted feet on solid ground as a base for snapping your torso. Full disclosure: I used this analogy when writing the original TI book 13 years ago. I have since come to see it as a weak analogy because of the significant differences between solid ground and water.
So what emphasis that will work reasonably well in water can you replace that one with? I have found that the following combination works well:
1) Have an intention to use your hands to "hold your place" in the water, rather than to push it back. Your hand will still move back; indeed to an extent it will still push water back. But that intention will cause you to engage core muscle more and arm muscle less.
2) Using the slight leverage offered by that gripping hand/arm, drive the "high side" of your body down. This taps the free energy available from gravity to assist in your intention. It also results in your swimming with your body, rather than using your arms to drag it through the water.
In freestyle, as your left hand is "patiently" establishing a grip, the right hip will be higher than the left. Rather than exert left-arm muscles to push water back, use them to stabilize your hold on the water as you drive the right hip down. Indeed think of using your right hip to drive your right hand past the gripping left. This should result in a sensation of sending energy forward rather than back.
Don't expect to get it on the first try. I've been working at this for seven years, and millions of strokes, and, though it felt promising from the very beginning, it still feels like a work in progress because I've had to undo 30-plus years of swimming with an intention to push water back. But unquestionably I'm using energy more efficiently now than previously.