Being in the personal training industry now for 25 years and counting, one of the most popular questions I get is "When should I do my cardio fitness training?"  I always recommend doing your cardio fitness training on opposite days of your weight training...but it is not always that simple for people...
Some people only have 3 days per week to workout.  Some only have 30 minutes each time they go to the gym.  And others don't even have weights to work with!!
Here is how I see the pecking order for cardio fitness training...

First Choice - Cardio fitness training on the opposite days of weight training.
Second Choice - Cardio fitness training on the same days as your weight training, AFTER your weight training!
Third choice - (Limited days to devote to fitness training) Use at least 2 days for weight training, and the other days for cardio fitness training.
Fourth Choice - (Limited time for fitness training) - Weight training 3 times per week, followed by a short, high intensity cardio fitness training routine.

The bottom line is getting it done, no matter what order or frequency...but if you really have questions seek out a fitness professional to help you get pointed in the right direction.

Resolve To Evolve,
Bob Mathews
Your Online Personal Trainer
Phoenix, Arizona

For Cardio Fitness Training Routines & Powerful Weight Training Routines - Click Here!