Blue to Red following a HIT workout and back to Blue within 24 hours is not unusual if the activity doesn’t raise low and high/peak recovery load sufficiently to push form into yellow/tired the next day.
If you view the your HIT activities and click on the XFAI report icon
you’ll see two pills in the upper right. For example:
which equates to this on the Training page:
In your case the red and yellow pills after the first HIT day may have been 0.2 and 0.0 meaning 24 x .2 = 4.8 hours later your calculated form is back to blue/fresh.
Other clues to determine the severity of a HIT workout:
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Difficulty of the HIT workout compared to your current TL status stars count.
If you’re at 3+ status stars and the HIT workout is 3-diamond difficulty and not very long, the workout won’t push you into red to yellow recovery. -
Do a quick calc of the XSS goal divided by estimated indoor workout duration to determine XSS/hour.
In the example above 186/2.3 = 81 XSS/hr. 2+ hours of that strain level was enough to trigger two days of yellow/tired (rest/easy endurance optional).
If a HIT workout ends up ~65 XSS/hr and is only an hour long, that’s a lot less strain to recover from. Back to back HIT workouts are possible.