I haven't been running for a while and I want to get back. I'm doing weight lifting 3 times a week. I just want to keep my fat gains minimal. is 45-60 min. on the treadmill or ellyptical enough @60~70%?

45 to 60 mins duration will always be enough so long as the intensity is correct.
what is the unit of intensity? HR max, VO2 max, lactate max? the essential component to weight loss is not the cardio side but the diet aspect. assuming that you have a healthy diet then working at 60-70% of your VO2 max would be perfect for keeping trim.

hope this helps

Daniel

well i'm an avge runner so my VO2 isn't that great. My diet is somewhat clean and balanced.

There is that great mis-conception when it comes to burning fat when running.

Do I run for 20 minutes at 80% MHR or do I run for 60 minutes at 60 MHR??

It really doesn't matter!

They will both get the same result in the long run. Obviously your diet does play a major role in lose/gaining weight. As long as your burning more calories than you take in (calorie depcit) you will burn fat.

I personally prefer to run for 50 minutes at 60% MHR as after about 30 minutes the energy used comes from your fat stores.

If you need any further help with training, nutrition visit my site: Exasko Elite Online.

Good Luck!

Hmmm, what kind of energy balance are you in... deficit, surplus, maintenance. I am trying to figure out why you want to run so much?