The average human lifespan is 25,915 days -- and that's the starting point for Reebok's latest spot, reminding us to make the most of the bodies we've been given. But while the insight -- use your body now because tomorrow you die -- might be depressing, an upbeat soundtrack and an inspiring story make this more of a feelgood ad as we watch a woman's lifetime of running prowess in reverse.

The film, by Venables, Bell & Partners, opens with an older woman running in a Reebok Spartan Race and ends with her as a baby in a crib -- along the way, we see her trail-running, jogging with a stroller, streaking across a college campus and outrunning a little boy in a childhood race. Michael Lawrence of Epoch directed the spot.

The ad dovetails with a social media campaign titled "Count Your Days" that allows users to calculate their potential number of remaining days, based on averages of age, gender and location. Visitors can share how they are planning to honor their bodies and their days remaining by sharing personal accomplishments via the hashtag #HonorYourDays and posting a photo to Instagram, Twitter or Facebook.