Low intensity – if you can sing your favorite song or carry on an uninterrupted conversation while exercising, then you’re exercising at a low intensity
Moderate to High intensity – If you can’t sing your favorite song and can only carry on an interrupted conversation (a conversation where you can only respond) then you are working out at a moderate intensity. Speech that is somewhat labored with a little huffing and puffing is a good test of exercising at a moderate-high intensity.
High to Very high intensity – Can’t talk at all. Have to stop and catch you breathe are signs that you may be working TOO hard at very high intensities.