People overtrain after getting hooked on positive feedback, one expert saidALAMY

Sports psychologists say that apps for running can be dangerous and that the NHS must recognise that too much exercise is a bad thing.

They say that more people are “overindulging” in exercise at levels just shy of addiction. In part this is driven by the prevalence of fitness tracking apps and trackers on watches and smartphones.

The apps are designed to keep people engaged and provide positive feedback, but Martin Turner and Andrew Wood of Staffordshire University say that this can lead to psychological harm as people’s self-worth becomes tied to the amount of exercise they do.

That may prompt them to skip rest days while training, even if they know they are necessary, causing physical injury. Professor Turner said that vast swathes of…