The January 13 issue of Science magazine contains a challenging article entitled "Birds don't need exercise to stay fit for epic flights." This title challenges the very root of my belief system. I preach and live by the principle that life's extent and content are direct results of fitness level, and physical exercise is the elixir that produces fitness.
The article cites the work of Lucy Hawkes at the University of Exeter in the UK where she is a physiological ecologist. She studies the bar headed goose. This animal is extraordinary. Its life pattern consists of summering and breeding in Mongolia and wintering in India, 3000 km away. Not only distant but high too with the migration route going directly over the Himalaya Range. I recall it can get pretty cold and oxygen deprived up there.
Hawkes and her colleagues were interested to see whether the geese gave any evidence of a training protocol before undertaking this exertion. The researchers fitted 31 geese with GPS, accelerometers, and miniature devices to measure pulse rate, body temperature, and altitude. They surveyed the birds before and after their flight to India and back.
The data revealed surprisingly that the birds did not do any extra activity in anticipation of their flight. Their pulse rate and temperature, both markers of fitness were unchanged before and after the flight indicating that they don't need exercise to stay fit. Hawkes predicates that the bar headed geese don't need exercise because they're better built than us humans for getting oxygen to muscle. When birds breathe, air goes not only to the lungs but also into internal air sacks that provide a continuous supply of oxygen to the lungs. And since they fly at such high altitudes they have evolved hearts that beat faster, have thinner lung surfaces, and are more efficient with their hemoglobin than other birds. Hawkes concludes that they're so good at getting oxygen and using it that they're already fit.
Other researchers study the barnacle goose which migrate from Norway, Russia, and Greenland to the UK, and they do not seem to increase their activity levels prior to the flight either. There seems to be some sort endogenous trigger that can trigger muscle growth without doing any exercise to trigger it.
Experimentally, when researchers try to induce extra exercise in birds they find that there is damage done by oxygen radicals and other charged molecules. There is an oxidative stress.
We humans are trapped by our physiology and anatomy in needing to exercise in order to yield the manifold benefits of fitness. The "use it or lose it" mantra still holds despite what the bar headed goose may tell you.