(Wall Street Journal) – More people are using the app to train for marathons. Its makers are adding ways to tone down plans some users found too aggressive.

To provide users with personalized plans and progress feedback, Runna uses a combination of human-programmed inputs, machine-learning algorithms and generative artificial intelligence. It can nudge you to go faster if you’re outpacing the program, just like a human coach. The difference? Human coaches cost upward of $120 a month. Runna costs that for a whole year.

For some users, Runna’s savings came with a hidden cost: an injury from plans they said were too strenuous. Numerous cautionary tales popped up on TikTok, Reddit and other social-media platforms. Physical therapists whom I spoke to said that each week, they saw multiple injured clients who used the app. (Read More)