While having an active job is good, it isn't really a substitute for dedicated exercise. Work activity tends to be a bit stop-start, and doesn't keep your heart rate elevated on a continual basis in the same way that dedicated exercise does.
Muscle soreness is a common response if you work them more than you are used to, and doesn't necessarily indicate a problem. But if you stop every time you get sore, you will never improve your fitness. Of course, it is important here to distinguish between generalized muscle soreness, and the sharper pain that may indicate a slight muscle strain or injury.
I agree that dedicated exercise will increase your fitness and the ability of your body to cope with the physical demands of work. A physical job should be a reason TO exercise, not a reason to avoid it.
The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man.
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