I became the unofficial team photographer for my daughter's cross country team last season. I purposefully didn't do track to give myself a break to catch up on other things. I feel like I should do it next year though. The field events might make it a little more interesting.
I found it interesting in the running photos I took, and I see it in your second picture here, the effect of gravity on the runners body on the 'downbeat' of their stride. It's where they've taken a stride and all their weight and energy is in a downward vector, and it pulls their muscles, skin, and even facial expressions down, often into weird contorting positions. The young lady on the left in your second photo is an interesting example of what I'm talking about. You can see she is on that downbeat, but since it's a sprint (I think), some of that force is more forward than the cross country runners I shot. She's also very lean and muscular. I think those things translate to the effect not looking too bad in your photo. You should see some of mine. Sometimes, I could barely recognize the kids. I suppose I need to work on my timing.