On the oxygen thing and following up recent lung-derived e-mails,
I have always been of the understanding that the highest SUSTAINED
energy turnover in humans is achieved by Tour de France cyclists and
Swedish woodcutters, but that these were only in the 4 times basal
metabolic rate region (correct me if I am wrong, as I don't have
refernces to back me up). There is a lot of literature from both
mammals and birds looking for the existence of and an explanation
for a proposed metabolic ceiling of about 5-7 X BMR, but it seems to
me that in the medium term (ie. not instantaneous & 'sprint' levels,
and not over the long-term, such as whole breeding seasons) birds
must surely take the cake.
A shorebird flying for 5,500 km is presumably expending energy at
anything from 10-15 X BMR (depending on your estimate of the energy
costs of flight) continuously for about 4 days. That is at a rate 3-4
times higher than what humans can sustain, for over a hundred hours
without a break!
Getting oxygen is of course only one aspect of getting your energy
going, and if anyone is interested in other aspects of fuel supply
(such as composition of fuel and problems with mobilising it) you
can't go past the recent issue of Journal of Avian Biology on Optimal
Migration, especially this paper:
L. Jenni & S. Jenni-Eiermann. 1998. Fuel supply and metabolic
constraints in migrating birds. J. Avian Biol. 29 (4) 521-528.
Keep up the good pondering, Phil.
Australian School of Environmental Studies,
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