Hi everyone, thanks for the suggestions.
Worked out the solution, I needed to give the array a value, so I just
on my after page loads I have this
javascript:var athleteList = new Array();
sessionScope.put("athleteList", athleteList);
So I changed my code to this and it worked. I obviously needed to initialise it differently
var newList = sessionScope.get("athleteList");
newList.length=0;
no idea why
var athleteList = new Array(); didn't work by itself, hopefully may help out some others.