The weekly bar on load profile is the average of the individual athlete's weekly sums.
Or in other words: Get the individual weekly sum for each athlete. Add all these weekly totals up and divide them by the number of athletes who did anything that week.
This is different from the stacked bar graph in the period report because the stacked bar graph shows the daily average for each day, and for only those athletes who participated that day.
So adding up the stacked bar values won't give the same results as is shown in the load profile page.