Great question — answering as the UphillTech team:
It's possible the answer will vary across countries/airports, however in many cases the limits you've mentioned are attributed to Occupational Health and Safety (OH&S) laws in the countries in question. These laws generally won't dictate the maximum weights themselves, but instead require employers to have in place a maximum amount that a single person (or two people working together) are allowed to lift. For many years the airline industry has used 50 pounds (23kg) as a standard for normal bags, and 70 pounds (32k) for 'heavy' bags (which would frequently require an additional charge due to their extra weight). Many airlines and affiliated companies (such as ground handing companies like...
Full answer by Doc: https://travel.stackexchange.com/a/204012 (CC BY-SA 4.0).
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