Unit 8 听力原文Part ICAn easy way to remember how much we need to exercise for fitness is to keep in mind the letters F, I and T:Frequency - 3 to 5 days a weekIntensity till your heart rate reaches your target speedTime -15 to 60 minutes each timeThen you may ask how to work out your target heart speed range. Lets do it together.The upper limit of your target heart speed range is 190 minus your age.The lower limit is 160 minus your age.For someon