  The decoupling of spin and density dynamics is a remarkable feature of
quantum one-dimensional many-body systems. In a few-body regime, however,
little is known about this phenomenon. To address this problem, we study the
time evolution of a small system of strongly interacting fermions after a
sudden change in the trapping geometry. We show that, even at the few-body
level, the excitation spectrum of this system presents separate signatures of
spin and density dynamics. Moreover, we describe the effect of considering
additional internal states with SU(N) symmetry, which ultimately leads to the
vanishing of spin excitations in a completely balanced system.
