Locomotion is essential for the survival and fitness of animals. Fishes have evolved a variety of mechanisms to minimize cost of transport. For instance, bluegill sunfish have recently been shown to employ intermittent swimming in nature and in laboratory conditions. We focused on understanding the functional properties of the power-producing muscles that generate propulsive forces in bluegill to understand the implications of intermittent activity. We report on the muscle activity parameters (e.g. oscillation frequency, muscle strain, timing of activation) of the aerobic muscle of bluegill during intermittent swimming. We also used those parameters in muscle physiology experiments to examine muscle power output during intermittent vs. steady swimming in these fish. Intermittent propulsion involves swimming at relatively slow speeds with short propulsive bursts alternating with gliding episodes. The propulsive bursts are at higher oscillation frequencies than would be predicted for a given average swimming speed. The muscle physiology experiments demonstrated that intermittent activity allows muscle to produce sufficient power for swimming compared to imposed steady swimming conditions. This work lends support to the fixed-gear hypothesis that suggests that there are preferred oscillation frequencies that optimize efficiency in muscle use and minimize cost of transport.