Imagine placing a tomato between the palms of your hands and applying direct pressure. It might take a great deal of force to burst the tomato. However, give the motion a twist while applying the pressure, and it will take far less pressure to burst the tomato. Twisting while lifting, pushing, pulling, lowering, or raising may have the same effect on the back. Consequently, if twisting while taking any of these actions exposes the back to much greater risk of injury.
Acceleration is the rate of change of the speed at which the body part moves.
The faster that back and forth motion occurs, the greater the risk of injury. Other factors like the weight of the object being moved, will also increase risk. Heavy Dynamic Exertion Work requiring heavy physical exertion places a greater demand on the body's cardiovascular system to provide the necessary oxygen and metabolites to muscle tissue. If a muscle group's demand for metabolites and oxygen cannot be met, that muscle group will become fatigued, increasing the risk of injury. When the muscle is tired and sore, it's fatigued, and injury may more likely occur.