Want to use a data from another form in a formula

Want to use a data from another form in a formula

Hi,

I have a form User with a list of user with some characteristic (one being MaxHR)
I have a second form RunningSessions which starts with selecting a User Name from the first form
I would like to create a field type = formula where an element is the MaxHR of the user selected above.

How can I do that ?

S�bastien