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The conclusion of a recent study reads:
Brief, intense stair climbing is a practical, time-efficient strategy to improve CRF in previously untrained women.
The study demonstrated that brief intense stair climbing improves cardiovascular fitness. This is the goal for activity. Just 30 min a week seemed to improve CV fitness.
The study had people climb stairs "intensely" in 60 sec or 30 sec intervals for 30 min a week.