According to the conversation, what is one problem with ann exericse?

W：Exercise, exercise, exercise. We hear so much about it these days, yet even the experts can‘t agree on which exercises are best. Now some doctors are strongly encouraging arm exercises.
M: Arm exercises? Is that because our arms are too fat or flabby?
W: Actually, that’s not the main reason. They say that arm exercises are an ideal way to become physically fit.
M: But don’t arm exercises raise your blood pressure?
W. That they do. But the article I read mentioned ways to compensate for that.
M: How?
W: By adding leg exercises, so the arms don’t do all the work. Arm exercises alone aren’t enough to increase metabolism before fatigue sets in. The more of the body that’s involved in the exercise, the better.
M: And in turn, I’m sure that there’s a greater chance of losing weight.
W: Sounds right to me.
M. So what exercises do the experts recommend?
W: They mentioned quite a few but some of the more popular ones are cycling with special bicycles that make you use both your arms and legs, and walking vigorously while you wear arm weights.
M: I must try that, I like to walk a lot.