The speed of the assemblers movements can be very fast. There are usually a high number of motions for certain stations. There are sometimes work policies that allow employees to perform high volumes of work, in very short times, in order to leave early. This puts a very heavy demand on the rest of the population that must follow this pace. When there is machine-paced work, especially at the higher volumes, it puts a good deal of stress on the individual.
Humans work in sporadic bursts, do a lot, then enjoy the feeling of accomplishment, and rest.
Machines are unforgiving and produce at the rate of the production schedule. Humans do not function well like this. There is psychological stress as well. Psychological Stess Studies have shown that 50 percent of the people that have upper extremity problems, also have low back pain as well. One day the back will hurt, the next there is pain between the shoulder blades.