The THR (target heart rate) refers to the minimum number of times the heart needs to contract each minute to have a positive effect on a person's heart, lungs, and blood vessels. This improvement is called the _________ effect. Intensity of activity below the THR will be insufficient to make a significant improvement in a person's fitness level. Although intensity below the THR will still help a person expend calories and lose weight, it will probably do little to make them more aerobically fit.
a) Training
b) Cooling
c) Warming
d) Cardiovascular