Running and Weightlifting.
Cycling is non weight bearing and doesn't help your bones.
In fact cycling at a high level, your body takes calcium from your bones. Studies have found even amateur racers with low bone density, because of this.
Hence weight bearing activities like running and weightlifting are good for maintaining bone density.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.