Well, you wouldn't say 'stair climbing' you would say 'climbing the stairs'. There's... climbing the stairs (emphasizes the height of the stairs, they're so many it's as if you are climbing up a hill) going up the stairs ascending the stairs The opposites would be... going down the stairs descending the stairs

If you're clumsy, the answer is "falling down the stairs."

climbing (up) the stairs climbing down the stairs

Ascending the stairs / Descending the stairs. "Stair climbing" sounds a little funny. I'd use "climbing the stairs".