Assume first that I will do this every day, and that I weight-train (BFL style) 3 times a week.

Which is better?

• 40 minutes at a steady 3.5 mph
• 20 minutes of BFL style (high-intensity interval training)

If you're not familiar with the BFL cardio workout, here's what you do:

• 2 minutes at very moderate pace (level 5)
• 1 minute at slightly faster pace (level 6)
• 1 minute a little faster (level 7)
• 1 minute a little faster (level 8)
• 1 minute a little faster still (level 9)
• Repeat the 6 - 9 sequence 3 more times
• 1 minute at peak performance (level 10)
• 1 minute at level 5 to cool down

So, what's the better workout?

The 20 minutes of HIIT. Go for it!

If you're trying to lose fat and not build endurance, I say the steady state cardio done in the morning before you've eaten is more effective. Keep your HR between 65% and 75% for 45 minutes+ and don't eat any carbs for an hour after.. P/F meal is fine.

Bawdy, do both.

I spent alot of time this weekend researching the same question,
What I've found (the short answer):
The low intensity, long duration (LILD) cardio is best for fat burning, while HIIT helps strengthen your heart/lungs........plus it's alot less boring.
When to do each depends on your lifting program.
Some say to do HIIT on your off days from lifting, and to eat protein prior and prot./fat after, just as for weights. I prefer to do my HIIT after lifting (and a short break, about 30min), as it is catabolic, and I figure then legs can rest the next day, but I'm finding that harder to do as my leg days get more challenging.
Now that I'm doing a CKD, the rules have changed, and I do HIIT 2 days a week, on off lifting days, and LILD 3 days.
As with everything else, you just gotta do something, and keep track of what works best for you.

Thanks, everyone! Here's what I think I'll do.

I'm going to do the HIIT workout on Monday, Wednesday, and Friday, a steady 3 mph 30-minute workout on Tuesday and Thursday (or even switch off the treadmill completely and do the stationary bike at a steady pace), and then on the weekends I'll do a longer 3.5 mph steady workout on the treadmill.

BFL-style weight sessions will be 3 times a week, with a day's rest in between. I'll probably start each day with the cardio, and then do the weight sessions in the evening. I simply don't have time to do everything in one stretch.

THANKS AGAIN!

Sounds perfect