听力原文：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. According to the conversation, what is one problem with arm exercises?