Running helps me to learn my own anatomy one sore muscle at a time. When a particular muscle gets sore, it's exact shape and location become readily apparent. It's as if the entire body is transparent except that one muscle, but instead of seeing it, I can feel it. It feels like a big bruised piece of meat inside my leg. Today that muscle is the fibularis longus. The fibularis longus plantar-flexes the foot. Plantar flexion is movement of the foot that flexes the foot or toes downward toward the sole. This is a muscle that I never knew existed until the non-stop steep ups and downs of the seven sisters trail race the other day. There it is, running down the front side of the leg.
![](http://district.bluegrass.kctcs.edu/rmccane0001/shared_files/bio137website/BIO137/137Lab8/Lab8Images/LegMuscles-names.jpg)
![](http://upload.wikimedia.org/wikipedia/commons/4/4a/Dorsiplantar.jpg)
It's nice to know that the soreness matches the obvious cause perfectly. I would imagine that plantar flexion occurs while pushing off when going uphill, and also to catch your fall with each downhill step (assuming a minimalist forefoot landing). The fibularis longus is also the most conveniently located muscle for massaging with a rolling massager. But ouch!
I hope you enjoyed your anatomy lesson for the day!