Question

What is the least amount of time you should stay in your target heart rate?

Answer 1

your body should start burning fat after 20 minutes in your THR... maintain for another 20+ will substantially increase your burn. You need to go longer, about 15-25 more minutes longer, to actually get your body burning fat..

Answer 2

To get the most use from your exercise, stay in your target heart rate range for at least 20 minutes during an exercise session.