Note to self...

50 minutes of exercise that never takes your heart rate over 120 is beyond your limits. So duration definitely counts.

Of course, that was starting off with some relatively intense exercise - the push to 120 came early. So maybe 50 minutes of easier exercise is within reach.

And maybe 20 minutes of exercise with a higher heart rate would have been better. Figure that out, someday after you've recovered.

This is going to be a long flippin' road.