Chapter 9: The Energetics of Aerobic Activity

The Energetics of Aerobic Activity introduces the concept of steady-state exercise, highlighting how animals performing long-duration activities rely heavily on aerobic pathways to avoid the inefficiencies of anaerobic metabolism. Researchers use methods such as treadmills, wind tunnels, and doubly labeled water to measure energy expenditure, and the chapter reviews how these techniques provide insight into metabolic rate patterns during different forms of locomotion. The text compares swimming, running, and flying, noting how the relationship between speed and metabolic rate forms different curves—U-shaped for swimming and flying, linear for running. The cost of transport (COT) is introduced as a measure of energy efficiency, with discussions of how animals optimize either speed or distance depending on ecological context. The authors explore how body size influences metabolic cost, showing that larger animals typically have lower mass-specific COT. The chapter then focuses on maximum oxygen consumption (VO₂max) as a measure of aerobic capacity, examining its variation across species and individuals. Examples include high-performance animals like pronghorns and endurance-trained rats. Finally, the chapter examines field metabolic rate (FMR) through real-world case studies of bar-tailed godwits and eels, showing how animals manage extreme migratory journeys with stored fat and physiological adaptations. Ecological energetics is introduced through bumblebee foraging and seabird colony energetics, underscoring how aerobic energy use is deeply tied to survival, reproduction, and ecosystem dynamics.