May be I needed to be more clear. Of course there can be variations, but the maximal potential iq is static throughout life and we can't change it. Good nutrition, good environement will help someone achieve it, I don't know about exercise.
For example, some IQ tests ask you "What's the next number in this series...". If you aren't very good with numbers, you might do very poorly on this section. However, if you sit down and learn about a lot of the patterns that show up frequently in those types of questions, then you may increase your score dramatically on that section, and thus improve your IQ.