Here's why: Unlike running, stair climbing has a vertical element.

Common activities such as running, swimming, and biking get your heart rate up, but none of them have the vertical element.

A splat is the vertical central element of a chair back.

For all its vertical elements, even basketball sometimes is reduced to how fast the feet can move.

These strong vertical elements would have distracted from the central figure.

The only vertical elements are the two dovecotes at the corners of the complex.

The large structural vertical elements support detailed glass and screens.

For that there was now a vertical element in the wind speed.

Side-scrolling segments with some vertical elements are an expected part of the game.

If the top member is sufficiently stiff then this vertical element may be eliminated.