Which of the following is true about target heart rate? 1) it is a measure of the heart rate after 20 minutes of exercise 2) it is a percentage of your maximum heart rate 3) it is the threshold level of exercise at which one cannot talk and exercise comfortably 4) it varies by a person's body weight?

Well if you pick a machine to work on and that's gonna be your exercise if you don't stick to that machine your muscle strength your muscle mass rather will change because you haven't been doing it you change something in your exercise routine which changes your body's form of dealing with things for example you might become weaker or stronger depending on what kind of exercises you do in whether or not the machine you picked actually your muscles grow.