running for fitness

Question
Hey,
I run about 4 times a week, and usually go to the gym on the other days and do the elliptical trainer and lift weights.  I don't do any competitive sport or anything, I just exercise to stay in shape and feel good and such.  My problem is that I don't vary my runs much.  I have some nice hills near my house (a 4 mile loop with lots of ups and downs) that I really enjoy running.  But I was wondering what you would recommend so that I can change up my routine some.  (for example, some days run two miles for time and some days run a longer distance at a slower pace, maybe do some sprints sometimes?). I am 5'7, 130 pounds, age 20.  
Thanks Ryan!
Maya

Answer
Maya,

You have the right ideas already. Somedays run the 4 mile loop[, others run the loop but within the run maybe pick up the pace for 30 seconds, then jog slowly for 30 seconds, then faster again, slower. Do this maybe 10 times during the run. You can also run easy for 10 minutes to a hil, then sprint up the hill, and jog back down. Do this 5-7 times and then jog back home. Once a week, maybe run 2 miles hard, and maybe once a week run 6 miles easy. Be creative with the run and it will be fun.

Ryan