if you want to compute a running rms value , you can use the movstd function - see help movstd
and use K = fs=8192 to average the computation over 1 second interval;
movstd Moving standard deviation value.
Y = movstd(X,K) for a vector X and positive integer scalar K computes a
centered moving standard deviation by sliding a window of length K
along X. Each element of Y is the local standard deviation of the
corresponding values of X inside the window, with Y the same size as X.
When K is even, the window is centered about the current and previous
elements of X. The sliding window is truncated at the endpoints where
there are fewer than K elements from X to fill the window.
now this will give you a rms calculation with the same time increment as your data, you can decide afterwards to plot only values with 1 second interval (so index values multiple of fs = 8192 )