How do you group identical work standards when conducting a musculoskeletal hazard investigation?

Hello, I am in charge of safety and health at a manufacturing company.
I am preparing for a musculoskeletal hazard investigation and am asking for advice because it is a bit unclear what criteria to use to group workers into the same task.
Even if people work in the same process, the specific tasks assigned to each person differ slightly, and there are variations in the equipment used and the frequency of handling heavy objects.
For example, even within the same assembly process, there are cases where one side works mostly sitting down while the other side moves materials while standing.
I am wondering if cases like this can be grouped as the same task, or if they need to be investigated separately if the work posture or number of repetitions differs.
It is also realistically difficult to investigate every single process individually for those with a large number of personnel.
I am curious whether you usually group tasks first based on the process name and then select a representative worker, or if the work posture and equipment used must also be similar to be considered the same task.
I would also appreciate it if you could let me know how the criteria are established in cases involving shift work or work rotations.