Nematodes are skin-breathers (cutaneous respiration). They absorb the oxygen they need for oxidative phosphorylation through their cuticle. Mitochondria in each cell, use the oxygen to make ATP to power cellular activities. But, worms are pretty good at surviving 24 hours or more completely without oxygen! Without oxygen, ATP synthesis is much less efficient. To adapt to no or low O2, the whole organism must reorganize its metabolism and alter its life history strategy. Part of this may be cellular changes accommodate differences in O2 and ATP diffusion, as well as the diffusion and transport of other metabolites. Building on a similar model of muscle energetic state, my lab and the labs of Dr. Stephen Kinsey (UNCW) and Bruce Locke (FSU) team up to model the energetic state of the whole nematode to address whether apparent energetic constraints are actual energetic constraints.