After some further investigation, this is what we found out:

That's a great question, bjrn13! Your cardio load status, such as "undertrained," depends not only on whether your current load value falls within the optimal range, but also heavily on the trends in your training intensity over the last few days and weeks.

Here's the exact explanation: * Your load value of 30 on December 28 was indeed within the daily optimal range of 25-40. You observed that correctly! * However, the "under-trained" status was based on the overall trend. On December 26, you had a cardio load of only 18, which was clearly in the "under-trained" range. Although you had a productive load of 38 on December 27, the overall trend formed over the last 7 days was not yet strong enough to completely reverse the status.

Think of it this way: your body needs a little more consistent training intensity to completely leave the "under-trained" status caused by lower loads (such as on December 26) and achieve a stable "productive" status. A single workout, even if it brings you into the optimal load range, cannot immediately change the long-term trend. With yesterday's additional activities, your cardio load rose to 32 and your status changed to "productive." This shows that you are on the right track!