I have a buddy who is into ultramarathon running. 95% of all his running takes place on trails. He is wondering what type of strength training would compliment this. The majority of his strength/cross training is core and stability work. Some plyometric type stuff to simulate the lateral movements you would find running on a trail. Wondering if anyone here does this and has a strength routine they'd share. I'm sure you could go with the basics of strengthening the legs and core. Thanks in advance.