Underwater, we humans can't compete with whales and other air-breathing marine mammals, which can stay submerged for extended periods. at the beach one day you meet a surfer who tells you that special training could allow her to swim underwater without breathing for an entire hour. from what you know of the respiratory physiology, explain why she is mistaken.

Getting submerged for an extended time period, that is, holding the breath for longer duration is not only associated with the issues of the lack of oxygen, however, it also is associated with the accumulation of carbon dioxide, due to the acidification of blood when accumulation of carbon takes place due to lack of breathing.  

The training as mentioned in a real sense slows down the rate of this acidification resulting the blood vessels to mediate the blood away from the regions like the feet and hand and reroute it to the brain and other vital organs. This training does not permit to hold the breath for a longer duration, however, hyperventilating on pure oxygen is done that is also known as lung packing, however, still it does not permit to hold the breath for more than twenty minutes. Therefore, the idea of holding the breath for one hour is totally unrealistic, though remains exciting.