Try something like this —
Fs = 5000;
T = 100;
t = linspace(0, T*Fs, T*Fs-1)/Fs;
s = sin(2*pi*t*25);
xrms = @(s, n) sqrt(movmean(s.^2, n)); % Calculate RMS Function, 'n': Window Of Consecutive Data
figure
plot(t, s, 'DisplayName','Signal')
hold on
plot(t, xrms(s,100), 'DisplayName','RMS(Signal)')
hold off
grid
legend('Location', 'best')
xlim([0 1])
The ‘xrms’ function produces the expected result of 
for the RMS value of a sine signal (after a short initial transient) over 100 data points (in this example).
for the RMS value of a sine signal (after a short initial transient) over 100 data points (in this example). .
