One of the best things you can do when you are regularly working out is to track your progress. There are two important reasons for this: you can see how far you have come, and you can make sure that your workout progress does not plateau but instead continues to develop.
It can be great motivation to look back a few months in a workout log book and see how much more strong and physically fit you are than you were previously. When looking for a good workout log book, you need to decide whether you want to simply record your progress in a notebook or blank journal, or if you would rather buy a book that is made specifically for the purpose of recording workouts. Some diet and exercise books come with log books that contain schedules and motivational phrases within the pages, and many people find this type of format quite helpful.
If you just want a simple book to record your workout progress then you don't necessarily need something elaborate. Just be sure that you choose an exercise log book that is easy to stash into your gym bag so that you actually take it with you and keep accurate records.