I have a little bit of experience with this and in short, unless you are very cleansed and healed it is probably something that will work out badly for you. To be clear that this is not a black and white issue, Dr. Shelton
has an entire chapter devoted to people while fasting who performed amazing feats of strength and such and includes a story about a guy who after fasting for a certain fairly large number of days ran a race against a reporter and soundly defeated him. But in most cases in today's world it seems that when people are fasting there is too much work to be done within their bodies for intense exercise to be practical and/or beneficial.
This was true for me as well in my little experiment with this where for 4 fasted days i performed intense cardio in the form of brisk uphill hiking. Everything i had read to that point said not to do this, but the explanation as to why was never clear and i wanted to see for myself what would happen. What i noticed especially after the 4th day was that my body was never calming down properly afterwards and even by the time i went to sleep... and even after a full night of sleeping 8 hours... my body was not appropriately slowed down, rested and restored, waking even with a mildly racing heart (maybe 80 bpm) rather than the 40-45 bpm that normal fasting had always led me to awaken to (even where substantial normal walking was included).
In summary, if you really wanted to exercise during your fast which i personally believe is a perfectly acceptable alternative for many people in many situations, particularly if you are in a fairly good state of health... and is supported particularly by many Russian fasting experts... i would encourage you to do something light to moderate or maybe even fully moderate, but not intense. Crossfit therefore which epitomizes high intensity is great outside of fasting, but i would recommend holding off on it during the fast.
To make my position completely clear, however, i believe that maximal cleansing and healing take place in a fast where we are moving around very little and laying down 23 hours per day. If a person wishes to sacrifice part of the cleansing and healing benefits to burn substantially more fat (a perfectly reasonable desire in many situations), then lots of semi-brisk walking can help accomplish that goal as in two or three hours per day without overwhelming the fasting body and keeping it from being able to fully recover each day.
Looking forward to your account. Many blessings.