Figure 5.

Power spectra of the magnitude of the three-axis accelerometer data each of the 100 balance and walking tests. The 200 densities are plotted on top of each other in order to see the maximum support that was observed at each frequency over all 200 tests. The shaded bars display the power spectra from the balance tests, and the colored bars denote the spectra of the walking tests. Since walking is highly periodic, in the spectra of these tests, most of the power is found in the lower frequencies associated with periodic walking. During the balance tests, periodic activities are observed for very short time durations, and the only periodic activity consistently recorded is the smartphone buzzer. This explains why we see that a lot of the power in the spectra is not found at the lower frequencies, but instead spread across the higher frequencies.