Based on my experience, I feel better with positive splits. However depend on previous long time training experience the body will adapt to the conditions, so an ex runner or swimmer in my opinion will be resistance to low intensity training. They should intensify their cardio to get result. Every body is difference. I read from a magazine that the more intens the cardio, the more far be burned. HIIT (high intensity interval training) is recommended, too long time running like marathon may reduce muscle mass and probably damaging muscle