According to the conversation, what is one problem with arm exercises?

W: Exercise, exercise, exercise, we hear so much about it these days that 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 of 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 exercise so the arms don’t do as they work. Arm exercises alone aren’t enough to increase metabolism before fatigue sets in. The more of a body that involves in the exercise, the better.
M: And in turn, I’m sure that there is a great 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 bicycling with special bicycles that make you use both your arms and legs, and walking vigorously while wearing arms weights.
M: I must try that. I like to walk a lot.