So there are ways to do physical labor that do not harm you, but a lot of these come down to management and are not up to the individual employee. You could definitely hurt yourself very badly if you do it wrong (which you won't generally do naturally -- our bodies give us lots of warnings -- but pressure from above can make you ignore those warnings and drastically shorten your working life).
Fortunately, the company where I did labor really tried to be a healthy place to work, and that made such a huge difference. A lot of my coworkers had been there for 30 years or more, and they were still zipping around like they were 20.
These are some things that really help:
- The work needs to not be too repetitive (you need to switch tasks several times a day, and each task needs to use different parts of your body).
- You need breaks. And not just at set times of day, but also just whenever you need it. If you do something to yourself that feels funny or not quite right (a warning sign that you are on the verge of a sprain or some other injury), you need to be able to stop working immediately until the feeling passes.
- You need to do work that is within your capability. It's OK to work extremely hard, to go home exhausted, and to feel muscle soreness the next day. But if you do something you're not strong enough or quick enough to handle with total control, you are likely to make mistakes that lead to injuries (tripping, dropping something, using poor form, etc.). Such injuries can be severe and lifelong, so you should absolutely never work at the edge of your ability.
- You need to be well-slept and well-hydrated (cold water and electrolytes should be available at all times, with absolutely no delay), and you must have appropriate clothing and a way to temporarily escape from the heat if you suddenly feel faint. You can work extremely hard under surprisingly harsh conditions (I did hard labor in humid, 100-110 F greenhouses day after day and felt great), so long as your body's basic needs are met.
There are proper postures to do a lot of activities and they are frequently not observed. Maintaining proper posture is a skill that must be trained until you don't have to think about it. Even something "mindlessly simple" like lifting a heavy object off the ground and carrying it somewhere requires proper posture and technique to reduce chance of injuries. Reduce, not eliminate. You can do everything right and still get injured.
When lifting things off the ground, most people will flex and extend the torso instead of using their much stronger leg muscles. The better form is to squat down by flexing the thighs, pick up the object then lift it up by extending the thighs, all while maintaining the spine aligned.
Physical education and conditioning is important in these jobs. In our every day lives.
This is one of several root causes behind our national opioid addiction epidemic. While pharmaceutical companies and doctors bear much of the blame, there are millions of people who suffer chronic pain from work injuries that can't be fully repaired.
Of course, some people take more precautions than others, and that helps, but it's no guarantee of safety.