They've offered bone-density scans, stress tests measuring oxygen consumption and the like, says Liponis.

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During the swims, the researchers measured the volunteers' oxygen consumption, rectal temperature, swim speed and angle, and stroke rate and length.

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Their oxygen consumption dropped 90%, and their body temperatures plummeted.

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People in this group were also the only ones who showed a significant increase in their maximum oxygen consumption (which measures the capacity for aerobic exercise) compared to the non-exercising control group.

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The mice's consumption of oxygen and production of carbon dioxide dropped ten minutes after they began inhaling hydrogen sulphide and remained extremely low as long as the gas was administered.

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