although I don't think it's a popular science book, 50% of the content is a training introduction that overlaps as much with strength training content as with other physical training books.
Pretty good, but not as good as Science of Running was. It still follows the same formula, discussing the technical aspects of the various strokes and how to optimize those, the anatomy and biology involved, a huge set of non-swimming exercises that will allow you to build strength and fitness in the pool and a solid training regimen you can use to go from barely making a length to putting up some pretty serious distance. I'd probably rate it 5 if I hadn't also read Science of Running when training for my first marathon (the running book was just more comprehensive by comparison, but that doesn't mean this book isn't comprehensive). If you can swim at all - even a little bit - and you want to get better and start putting down some work outs in the pool, this is a great book. I'm still working through some of the training plan and use many of the complementary exercises every time I hit the gym. I should also note that a lot of the exercises described can be done at home with nothing more than a mat, and there are a number you can add barbells, dumbells, resistance bands, etc.