Acoustic waveforms were recorded every 60 seconds while cycling. This produced a dataset of 66,995 waveforms, with similar contributions from the different cells (Table ). An example waveform is shown in Fig. . It comprises a total of 4000 data points which correspond to a duration of 10 µs. The 9 peaks circled on the waveform are peaks that could be identified consistently for all cells under all cycling conditions thanks to their adequate prominence. They will later be used to form certain configurations of acoustic features. The final peak is widely believed to originate at the posterior side of the cell and can be termed the 'back wall echo' peak. As a convenient feature to visualise, the time-of-flight (ToF) of this 'back wall echo' peak is also plotted in Fig. .