When you work a physical job you are typically working for 8-12 hours straight with little break and you often do repeated, but non-ergonomic activity that lead

When you work a physical job you are typically working for 8-12 hours straight with little break and you often do repeated, but non-ergonomic activity that leads to joint damage such as standing on hard floors for 12 hours; bending over repeatedly with poor form to pick up a heavy tool; kneeling on hard floor; etc. Often, because of the long hours and fatigue, individuals resort to bad form to rest their tired muscles. Working out for leisure activity, however, is often higher intensity for a much shorter period of time and typically very controlled ergonomically to reduce joint stress / wear. Professional and enthusiast lifters know that when you can no longer maintain proper form you stop lifting. Runners train and build their bodies over a year or more to handle up to marathon distances. When it is your occupation you don’t have such a luxury, so bad form happens immediately and repeats for an entire career. Further, people who work out are usually making a conscious effort to improve health and make dozens of other small decisions such as improved diet and hydration that would be difficult to account for or control in a study. A nurse, plumber, or construction worker may be in good physical shape and making healthy choices or not. If they are not they are putting more physical stress on their body. A runner is making on e very clear healthy choice that probably correlates to a bunch of other healthy choices.