This was done in order to achieve the maximum conservation of our life-support capabilities, basically food and air.
9 seconds sound clip from the 2001: A Space Odyssey (1968) movie soundboard.
You can hear this line at 01:00:15 in the Blu-ray version of the movie.
Quote context
[...]
- Marvelous. We have no complaints.
- Now, the three hibernating crew members represent the survey team.
- Their efforts won't be utilized until we approach Jupiter.
- What's it like while you're in hibernation?
- As I understand it, you only breathe once a minute. Is this true?
[...]