| CPC A61B 5/0245 (2013.01) [A61B 5/0816 (2013.01); A61B 5/349 (2021.01); A61B 5/352 (2021.01); A61B 5/6823 (2013.01); A61B 5/7203 (2013.01); A61B 5/726 (2013.01)] | 8 Claims |

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1. An apparatus comprising:
a communication circuitry configured to support a wired or wireless communication technique;
at least one processor; and
at least one memory including a computer program code, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to perform operations during a physical exercise of the user comprising:
acquiring a heart activity measurement signal of a user, wherein the heart activity measurement signal comprises QRS complex waveforms and characterizes electric activity of the user's heart and is measured by at least one electrode pair configured to contact with the user's skin;
performing a wavelet transform on an in-phase (I) and quadrature (Q) components of the heart activity measurement signal;
computing a phase component of the heart activity measurement signal by determining an argument of the wavelet-transformed in-phase (I) and quadrature (Q) components of the heart activity measurement signal;
determining periodicity of the phase component of the heart activity measurement signal and determining a respiratory rate of the user from the periodicity of the phase component of the heart activity measurement signal; and
performing at least one of outputting the respiratory rate to the user via a user interface of the apparatus and transmitting the respiratory rate to another apparatus via the communication circuitry.
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