Basal metabolic rate generally scales with body mass in mammals, and variation from predicted levels indicates adaptive metabolic remodeling. As a thermogenic adaptation for living in cool water, sea otters have a basal metabolic rate approximately three times that of the predicted rate; however, the tissue-level source of this hypermetabolism is unknown. Because skeletal muscle is a major determinant of whole-body metabolism, we characterized respiratory capacity and thermogenic leak in sea otter muscle. Compared with that of previously sampled mammals, thermogenic muscle leak capacity was elevated and could account for sea otter hypermetabolism. Muscle respiratory capacity was modestly elevated and reached adult levels in neonates. Premature metabolic development and high leak rate indicate that sea otter muscle metabolism is regulated by thermogenic demand and is the source of basal hypermetabolism.

基础代谢率通常与哺乳动物的体重成比例，与预测水平的差异表明适应性代谢重塑。作为生活在冷水中的产热适应性，海獭的基础代谢率大约是预测的三倍；然而，这种高代谢的组织水平来源尚不清楚。由于骨骼肌是全身代谢的主要决定因素，我们对海獭肌肉的呼吸能力和产热泄漏进行了表征。与先前采样的哺乳动物相比，产热肌肉泄漏能力有所提高，可能是海獭代谢亢进的原因。新生儿的肌肉呼吸能力适度升高并达到成人水平。