Manual assembly workstations are part of production processes that maintain a sequential operational dynamic, where the sequencing is structured based on the standard time assigned to each productive activity and the transportation time from one workstation to another. The standard time is defined based on the productive capacity of an average operator, plus the combination of tolerances and performance ratings that describe the operator's behavior in performing their task, maintaining this time throughout the workday. This situation conceals a differential between the operation's cycle time and the defined standard time, framing a chronological growth throughout the workday in the cycle time when the workstation does not involve ergonomic guidelines, mainly due to the activity's characteristics, such as high repetitiveness, monotony, high concentration, low locomotion, and short cycle times. This research is based on a multivariate classification of manual assembly workstations, showing an increase in cycle time of up to 70%. This increase is due to the effect of fatigue on the worker and entails an implicit decrease in production volume, reducing the company's profitability and affecting the operator's quality of life.