Assuming you can get the locations of the peak, you can create an id variable.
% acc = ... m x 1 array
%locationidxofpeak = somefuntion....
strideid = zeros(length(acc),1);
strideid(locationidxofpeak) = 1;
strideid = cumsum(strideid);
% now stride id would be like [0 0 0 0 0 1 1 1 1 1 2 2 2 2 2 ....]
for i = min(strideid):max(strideid)
strideacc = acc(strideid == i);
% your code.
end
