Once upon a time, as a lowly student, I had a job that solely consisted of lifting 25kg sheep food blocks off a conveyor belt and onto a nearby pallet until there was 1000 kg, then a fork-lift would come to take it away for wrapping (a far better job), and repeat. I think I topped out at 60-70 pallets in a twelve-hour shift. Australians, of course, are not as strong as Brits.
When I worked in the brewing industry, I regularly measured my days in tons. My record was shifting 11 tons of beer across two 8 hour shifts. I was really starting to go crazy by the end of that one. Lifting 300kg of grain into the hopper, then an hour or so later, digging it all out when it was at about 65°C. Was a great work out.
I was getting quite fit by the end of it, and could easily carry a 30l keg one in each hand (It was better balanced than carrying just one).
But it's bloody stupid. Sure we can lift 25kg blocks of sheep food, or toss around 50kg casks of beer. But we really really shouldn't. The amount of people who injure their backs due to manual handling accidents every year is costing the economy way too much.
It's also worth noting that picking up a 15kg bucket from the floor to the table, is very different, than say picking it up from the table and holding it up at head level to pour into some mixing machinery.
J