Fitness bikes and cross bikes

Is not actually every bike a fitness bike? After all, even if you only use your bike for your daily commute to the office, you're getting on a piece of sports equipment and getting some exercise in the fresh air... sounds a lot like fitness, doesn't it?! So what can a fitness bike do better than other two-wheelers? We introduce you here to the sporty, lightweight all-rounders and tell you when a fitness bike or cross bike is the perfect vehicle for you.