Humans voluntarily seek out ways to exercise and be active in lifestyles that are otherwise sedentary for a big part of the working populace. From playing sports, running marathons or lifting weights at the gym, people make staying fit a priority - but are we the only species that does?

In the latest study, researcher Dr. Lewis Halsey of Roehampton University tires to answer this question. However, the results are not all that conclusive - we still don't know if animals necessarily exercise to "keep fit." 

But here's what we do know: 

Animals rely on intermittent foraging to acquire energy-rich foods, which they need to support them in their routine activities of predator defense, locomotion, and mating. 

Humans also consume eating energy-rich foods and compensate for weight gain by exercising.

Therefore, Dr. Halsey was interested to see if some animals also need to spend time and energy on voluntary exercise so that they are fit enough to out-run predators, win over mates or hunt down prey. 

"Researchers haven't contemplated the idea that some animals may not do enough exercise during their general activities to be suitably fit for infrequent, high-intensity activities such as fleeing from predators. This needs to change," Halsey said in a news release. 

We also know animals will change their body condition in response to environmental conditions. For example, songbirds gain some weight to survive the winter, but not so much that they can't escape predators. 

On the other hand, when there are no predators around to fear, animals will pile on the pounds. Laboratory animals, for instance, gain weight in captivity. Like humans, however, they will burn excess fat by "exercising" -- when given a wheel, mice, rats and hamsters will spend countless hours running round and round.

Contrary to humans' need to push themselves harder at the gym after a "cheat day" or holiday full of sweets, some species are able to maintain their fitness with little to no exercise at all.

In his study, recently published in the Journal of Animal Ecology, Halsey points out polar bears and penguins burn different tissues while fasting in the winter, rather than through voluntary exercise. And polar bears stay fit during hibernation by maintaining their muscles, ensuring they don't awaken in the spring a weakling.

Barnacle geese appear to be an extra-special case of getting fit quickly: Some populations migrate nearly 2,500 kilometers each autumn from Svalbard in northern Norway to Scotland, but in preparation for such strenuous travels the geese fly for only a few minutes each day, in short bursts of flight, which Halsey compares to modern high-intensity training (HIT) regimes human athletes use to boost maximal aerobic capacity.

"Barnacle geese appear to get fit for certain predictable, planned events such as migration, and yet miraculously seem able to do so with little or no voluntary exercise," He added. "So their bodies seem to trigger increased fitness from within - they get fit automatically when they need to - enough to make any human with a waning New Year's resolution to get fit very jealous."

If animals are voluntarily working to "keep fit," they would need to tap into their energy reserves. Understanding this opens a whole new window for studying animal behavior, Halsey said. "No one has previously observed animal behaviors and thought 'this behavior could be associated with keeping fit." 

Another study, recently published in the journal PLOS ONE, focuses on young humpback whales, who appear to work out in extended sequences of breaching. (Scroll to read more...)

For their study, researchers from California State University, Channel Islands, examined whales' myoglobin, which is a protein found in the muscle cells of animals and is responsible for storing oxygen. In terms of humpback whales, however, only young calves are seen "exercising." 

"These high levels of exercise have always been something of a paradox," co-author Rachel Cartwright said, "given the limitations on maternal energy resources during the breeding season."

In total, Cartwright and her team studied muscle tissue samples from 18 stranded baleen whales, and compared muscular myoglobin stores found in both young and adult baleen whales. Since whale calves develop oxygen-carrying myoglobin as they mature, researchers suggest exercise may drive may be crucial part of the animals' early development.

"This study provides a functional explanation for these high activity levels; this intense exercise drives development of oxygen stores in the muscle tissue, allowing young whales to build their breath-holding capacity and make sustained, extended dives," Cartwright added. 

These studies combined reflect how working out may be more common in the animal kingdom than previously thought. 

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