HRV data were obtained using the ballistocardiography technique, using accelerometers mounted to next-generation moving microchips (Ramos-Castro et al.
On another note, we wish to point out that in this study, HRV was recorded using the ballistocardiography technique, taking advantage of the accelerometers already built into players' smart phones.
In a technique called ballistocardiography
, a heart patient would lie on a table with a low-friction suspension system; with every heartbeat, the table would move slightly, with a displacement corresponding to cardiac output.
Noninvasive methods of heart rate measurement, such as acoustocardiography (12,13) and ballistocardiography, (8,14) are also described.
Ballistocardiography measures small vibrations of the eggshell; the resultant signal is increased and processed in a microcomputer.