Every runner has their Achilles heel. Some of yours might literally be... your Achilles. Mine are my knees. I had my meniscus repaired twice and finally had a chunk taken out. My tibia is twisted, so my I have one "flippy" foot that really grinds that cartilage. Not much to be done there. I just work with it.
But there are things working against my knees that I can control: the muscles that support healthy knee tracking. One of the main muscles that attribute to a strong, healthy stride are the hip abductors. As ladies the angle between the hip and the knee is often more severe then the dudes. Yes, even little hip ladies.
Every time my knees act up and I seek physical therapy, they tell me to strengthen my hip abductors. After they laugh at how weak they are.
Here are two exercises you can incorporate into your strength training to support your knees.
1. Leg Raises on the Ball: You'll 'feel the burn' on the supporting leg too. Oh, and your hip abductor in Sarah terms would be your 'side butt'.
Sketch by my Physical Therapist, eerily close resemblance.
Another view - I look different from behind
2. Hip Hike: Use a book, a weight, a stack of magazines, a curb... anything 3-4 inches off the ground. Stand on object with one foot, hover other foot next to it, 'drop' hovering hip and hike it back up to hover next to standing foot. You should feel the burn after 5 or so. It's a small movement but you will feel it in the stabilizing leg.
12 x 2 each side.
As a runner what is your Achilles heel? And how do you ward off injury?