OOPS
INJURY PREVENTION
Whether working in sitting or standing, unless your job requires a lot of moving around into different positions and taking a rest or a frequent easy walk between tasks, you should take an exercise break at least every two hours and even every half an hour especially for leaning or bending or repetitive reaching work.
Any single task you are doing, even if sitting working at a computer, will bring the stabilising muscles of your body to fatigue in 30 minutes (1/2 hour). Fatique in stability or core muscles will alter the posture of the body during the task, and that alteration will create more stress on action muscles, leading to an overuse injury.
For heavy tasks, every few lifts may bring your stability muscles and action muscles to fatique. Failure to rest will lead to inadequate stability for your body. either the load will sag onto tissue, or the muscle might work in a faulty manner, causing an injury.
Fatique is noticed by not being able to hold your position comfortably or confidently while doing the task at a low speed.
The exercises here are the most likely exercises you will need to release fatiqued muscles and reverse any tendency for stiffness in joints and muscles.