They would give you conditional letters of offer. You would have to go to a gym and you would have to demonstrate that you could lift that amount of weight before they would even look at you.
That has changed. The industry now is being more open to women, people with disabilities, and other segments of the population that would allow for other sources of labour. That wasn't always the case. The use of tele-mining, robotics.... The days of operating a jackleg are not completely gone, but they're certainly becoming few and far between.