When you’re lifting heavy things for a job, you lift whatever needs to be lifted in whatever motion it needs, with incentives to do it quickly. If you’re tired, you lift it anyway. If you feel a twinge, you probably ignore it because it’s probably nothing. Then you do it again the next day regardless of whether you feel like it.

Some of that can be mitigated by workplace rules, but it needs pretty radical overstaffing or acceptance of considerably slower work, neither of which Capital is a big fan of.

As a lifter you have full control over how many reps you do, you have all the time in the world to make sure your form is good before lifting, you don’t need to move around while carrying that weight, and you’re lifting conveniently-shaped weights.

Also, even the most well-maintained mechanical device will eventually suffer from material fatigue when put under load for significant amounts of time. Our bodies are no different.

A "sane" max limit is 30 kg for a "normal" worker in good shape, so the 25 kg makes a lot of sense.

There was a precise technique to lift the 50 kg sack and put it on your shoulder, one single, tiny mistake in the speed or in the amplitude of the movement and it was very, very likely you would strain your back.

In the old times it was rather common as an accident on building sites, and anyway even people that never made a mistake have had their backs ruined over the years.

The "main" study/manual on the matter is actually US originated, by NIOSH, dating to 1994, that has been recently updated:

https://www.cdc.gov/niosh/docs/94-110/default.html

not limited to construction only, it applies on whatever activities imply moving loads, particularly if in a repetitive manner.

Technically correct I guess? The thing is, in construction there is a lot less latitude for you to choose a) from where to lift b) where to put down c) how much you're going to lift d) how often.

> So the question then becomes: is this about technique? Are these labourers lifting with their backs, for example? Are they just never taught to lift things correctly?

rolls eyes

Mostly. In your gym lifting, do you do 300 reps a day? For five or six days per week? For 48 weeks of the year? For ten to forty years? I bet you have more rest days than that.

> is this about technique?

Technique is impossible to apply consistently in blue-collar jobs. You're not necessarily standing on a flat, stable, firm, grippy floor, lifting a stable, ideally-shaped, easily grasped, rigid, non-slippery mass straight up and down close to your torso. There are wind, rain, cold, heat, and much more to deal with.

> Labourers can be taught

This is broken thinking. For health and safety, tasks must be redesigned to fit humans, not the other way around.

Edited to add: humans get tired, get distracted, take shortcuts, hurry to get the job done, or simply make mistakes. Any task design that doesn't account for these and still keep people safe is faulty.

Part of it is that you find yourself having to lift in awkward positions often while you're having to carry heavy materials through obstacle courses, up on ladders and down stairs in ways that you'll inevitably have to compromise optimal form all while the wage clock is ticking so you have to hurry. In weightlifting you're afforded proper time and place to practice good form. That's coming from a Carpenter for twenty years and a weightlifter for four. Carpentry and a vehicle wreck pretty much destroyed my back but weightlifting and what I've learned from it has helped restore it somewhat.

The human body needs to run in a pretty thin zone of activity. Too little and you get the obesity issue, too much and if breaks. And that band is changing as you age.

If that physical activity is by choice and easily changed you can stay healthy a very long time, but that’s not how it is when it’s your job.