Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Easy to read but exercises too hard

I had been running for years and had also done a few marathons when I decided to use a heart monitor. As I saw lots of 5 stars for the book I decided to buy it. In my opinion it asks too much of the runner. I reached a point where I dreaded to run on certain days because of the book. My rest heart rate was 51 and my maximum heart rate was 199. Even at novice level I had to run at 85% several times for 400 yards or 800 yards. I think it is a must to use a heart rate monitor but don't use the programs the author suggests. For German readers I suggest Ole Petersen's books "Ironman" or "Marathon".