The boxers had sought higher altitudes to train.
Climate change is sparing the highest altitudes to some extent, some climbers say.
The programme, called "Project Loon", involves fitting transmitters to the balloons, which will fly at similar altitudes to Facebook's drones.
"Individuals must migrate and choose the right winds to fly at different altitudes to maximise the efficiency of their migration.
Women moving from low altitudes to high ones also have more trouble delivering oxygen to their babies during pregnancy.
We were approaching similar altitudes to the highest European mountain, Mont Blanc, at 4,800m, and the lack of oxygen was starting to bite.
Among its features, the development will boast a new vacuum facility that, together with existing test cells, will allow high altitudes to be simulated for rocket testing.
The 16km-walk is intoxicating: visitors descend down steps from near-Alpine altitudes to the bottom of the gorge in pine forest.
Airlines like their planes to climb fast, to reach thinner air where flying takes less fuel, but they will accept lower altitudes to cut delays, officials said.
Some kikik (kite) owners aim to fly their kites to extraordinary altitudes, to lead them through spectacular maneuvers, or to keep them airborne for as long as possible.
