Why the seven-time Grand Slam champ and serial entrepreneur is backing a startup that bills itself as the Duolingo of walking.

Venus Williams has signed on as an investor and brand ambassador for the app, which incentivizes walking by offering rewards.

The tennis star will invest in and promote the app, which offers users rewards for walking and visiting specific sites.

The market for walking apps is heating up. One contender, WeWard, has been backed by Grand Slam tennis champion Venus Williams.

Venus Williams wants to get people walking. The tennis star, who recently released her health-focused book "Strive," has joined the app WeWard as a brand ambassador and investor. Through her role, Williams will be featured in a new advertisement,