I guess I'm not sure how you want these to concatenate together...this sounds more like a radiobutton?

Anyhow - you can use if..then logic to look through each checkbox:

PHP Code:
if(checkbox1.selectedvariables.txtMessage 'Find Your Pace';
if(
checkbox2.selectedvariables.txtMessage 'Stress Escape';
//  ... 
Or you could combine these into one big string or something (again - not sure how these are supposed to work if more than one is selected):

PHP Code:
variables.txtMessage '';
if(
checkbox1.selectedvariables.txtMessage += 'Find Your Pace, ';
if(
checkbox2.selectedvariables.txtMessage += 'Stress Escape, ';
//  ...