Observing more than 15000 penguins, some diving for food, others foraging holes in the ice, and others free diving. On average the birds flap their wings 237 times on each dive. Flapping underwater has the same affect as birds flapping in the air; it allows the penguin to dive and surface aqua-dynamically.
Dr. Shiomi, from the University of Tokyo stated he believes penguins' dives are constrained by how much power their muscles can produce after every pre-dive breath. Accordingly, penguins begin their ascent to the surface about 5.7 minutes into their dive, allowing enough energy to return for the next breath.
Although there are similarities to how humans have learned to measure underwater, the penguins' execution is fundamentally different. Dr. Shiomi states, "that the [penguin's] decision [to return is] constrained not by elapsed time, but by the number of strokes and thus, perhaps cumulative muscle work."