% setup vars
t = [0, 1, 2, 3, 4];
p = [0, -2, -5, -2, 0];

% generate graph lines
querypts = 0:0.001:4;
interpts = interp1(t, p, querypts, 'spline')';

ret_LHip  = [querypts', interpts];
ret_RHip  = [querypts', interpts];
ret_LKnee = [querypts', interpts];
ret_RKnee = [querypts', interpts];

% create graph
%figure
%plot(t, p,'o', querypts, interpts, ':.');