Lifting weights helps me. They don't need to be heavy, even using body weight, i.e. squats, lunges, pushups, Burpees, helps keep the muscle and burn the fat.
A friend of mine bagged a top-3 at Boston in the F70 group a couple years back. She says the only way to stay lean enough to run well is to eat like a bird. Probably not the answer you were hoping for.
Around here the birds (crows and sea gulls) mostly subsist off french fries from McDonalds and places like that, supplemented with trips to the city dump to find whatever morsels and delicacies they can glean there.
"Possum's" advice is close to Dee's belief that her weight training for decades has helped. Using body weight workouts is a lot like the Dog Days workouts (the 6 pm workouts at Lawrence High track begin in June, if you want to try a workout).
Thanks for the weight lifting and other advice. I'm frustrated because I've been weightlifting regularly (with a trainer) for 3 years. My muscle tone is not what it used to be.