Focusing on 3 mph (4.8 km/h) and looking at the frequencies
and accelerations of the harmonics provides more insight into the
large variation in power output. The acceleration amplitude and
frequency of the first 5 harmonics of the step frequency are shown
in Figs. 17 and 18. The amplitude ofthe 3rd harmonic, which is close
to the resonant frequency, has a mean value of 0.057 g, but has a
standard deviation of 0.019, or 33% of the mean. Additionally, the
frequency of the 3rd harmonic has a mean of 5.77 Hz and standard
deviation of 0.36 Hz, or 6% variation. With such large variation in
acceleration and frequency, it is expected that the power will vary
quite significantly.