Fig. 4: Interference immunity of electrical noise.

a Signal outputs during fast walking (walking frequency ~0.8 Hz), showing that sports cause limited noise amplitude. Tests were carried out with the SE attached on a thumb. Inset shows pulse signal and motion artifacts. b Frequency-domain analysis of the pulse signal with motion artifacts. c Continuous wavelet transform of the same signal in panel (a), revealing temporal dependence frequencies which coincide with the onset and termination of intense physical activity.