obviously I have misunderstood something myself.
What is it you are trying to do with this form? do you want the hidden element to contain the First name from the first record of the recordset?
The basic problem is this:
The form is after the repeat region.
once the repeat region loops through the recordset, the recordset is at the end, on an empty pointer.
your H1 tag works because it is before the repeat region, before the repeat region, the recordset is on the first record. so the h1 shows the first name contained in the first record?
is this what you want in the hidden element? the first record value? if so, you need to reset the recordset to beginning;
$row_Activities = mysql_fetch_assoc($Activities);