Participants sprint up a staircase in the November Project fitness workout at the Presidio in San Francisco on Friday, Aug. 31, 2018. Paul Chinn/S.F. Chronicle People who do more short bursts of vi…

Participants sprint up a staircase in the November Project fitness workout at the Presidio in San Francisco on Friday, Aug. 31, 2018. Paul Chinn/S.F. Chronicle People who do more short bursts of vi…



