In structures with modes that have lower natural frequencies (less than approximately 4 times the maximum footstep frequency), it is possible for the dynamic response to build up (increase) over time. This is caused by a phenomenon known as resonance and occurs when the frequency of the excitation closely matches the natural frequency of a vibration mode of the structure. Resonance is most likely to occur when the walking frequency matches the natural frequency of the structure, but it is also possible when any of the first four harmonics of the walking frequency (f_w , 2f_w , 3f_w ,4f_w) match the natural frequency (f_n ). Resonance at higher harmonics is much less likely.

In structures whose fundamental mode of vibration has a natural frequency larger than about 12-15Hz, the dynamic response of each footfall tends to dissipate almost entirely before the next footfall. This type of response is referred to as impulsive because a buildup of response due to resonance is not likely in this frequency range.