Intervals will burn more calories, and elicit a much greater response from your body than just riding along at any given pace.
Try this:
15-20 min warm up
- 10 minutes easy pedaling
- A few one leg isolated-pedaling drills
- A couple 30 second spin-ups
5x5min intervals
- Go at a pace you could only maintain for 5 minutes (HR zones 4 to 5 if you know them, Around 90-95% max power)
- Rest 5 minutes by pedaling at an easy pace.
- Repeat.
Warm down
- 30 second spin-ups
- 5-10 minutes easy pedaling
At 45 minutes of "power riding," our bodies aren't capable of maintaining a consistently difficult pace, and won't adapt or get stronger. We can't go hard enough over that long of a period of time to get our bodies to respond to any particular training load. The idea behind interval training is that you go so hard during your interval, that you overload your body, which is then forced to compensate by getting stronger in the long run. There is much more science behind the concept, but this is the general notion.
The best workout for burning fat is to go around 65%-70% max power for a LONG time. Long Slow Distance or LSD riding will burn a lot of fat. Calories are Calories though, so if you want to get the best bang for your buck, intervals definately burn more calories per hour - just be aware that lots of these calories are going to be coming from glycogen, and not fat, so you have to take particular care to recover from interval workouts by including enough quality carbohydrate in your diet.
