I was going to make some wisecrack such as "They say hard work never killed anyone - but I am not taking any chances", - before realising that this is indeed a serious matter.
Repetitive Strain Injury (RSI) is a rather common condition. One of its many sufferers is my wife, who worked for a number of years on an assembly line. Her only task was to lift the cartons of packaged garlic bread off a conveyor line and stack these on a pallet. While the cartons were not particularly heavy, just the sheer rate of repitition was enough to, in the end, cause irreversible injury to her back.
With the wisdom of hindsight, industry now realises the importance of rotating tasks around, so that nobody is performing the same repetitive movements for prolonged periods of time. Also, ergonomics plays a part; such things as the position of the computer's display relative to your eyes, position of the keyboard relative to your elbows, the height of your chair off the floor and its providing adequate lower-back support all play a part.
Of course, getting older doesn't help! There is a danger in that as young persons, we can seemingly get away with a lot - as in the handling and lifting heavy objects. It does come back to bite you, though, when you get older!