Back to back workouts

Is there a way to notify Xert that you have completed two workouts back to back? The MPA resets after the first workout, but in reality you are starting the second workout under fatigue.

No. Depending on the workout, MPA will reset during the first workout and during the cooling down. Xert cannot (currently) factor in how that impacts your MPA, going into the second workout, if at all.

It will measure your fatigue and give you the appropriate workout suggestion, depending on your XSS status.

But I can completely drain myself during a long activity and never even pull MPA down by much. I may then get a suggested workout I will simply not be able to complete.

This has been discussed before and modelling in this kind of action / fatigue is apparently extremely difficult. Xert is not factoring in that you will / could do two workouts back to back - it will advise you a workout that WILL drain you enough to never even want to start another, IF you pick one from the library that you think you can handle.