Abstract: A method of estimating a stress level of a human by an apparatus using heart activity measurement data includes: executing a breathing exercise application by the apparatus, starting a breathing exercise of the breathing exercise application and outputting, during the breathing exercise, breathing instructions to a user of the apparatus; acquiring a set of heart activity measurement data samples measured by a heart activity sensor from the user during the breathing exercise; computing a set of inter-heartbeat interval samples of the set of heart activity measurement data samples; computing a cardiac coherence of the user during the exercise from the set of inter-heartbeat interval samples; measuring a respiratory rate of the user during the breathing exercise; computing a score of the breathing exercise on the basis of the respiratory rate and the cardiac coherence, the score indicating a stress level of the user; and outputting the score through an interface of the apparatus.

Abstract: A method and an apparatus for performing the method are disclosed. The method includes obtaining cardiac output power data on a user; obtaining kinetic data characterizing physical exercise intensity of the physical exercise performed by the user; detecting that a measured cardiac output power exceeds a first threshold or that physical exercise intensity changes according to a rate exceeding a second threshold; upon the detecting, determining a synthetic cardiac output power parameter based at least partly on the kinetic data; and outputting the synthetic cardiac output power parameter.

Abstract: A method and an apparatus for performing the method are disclosed. The method includes obtaining cardiac output power data on a user; obtaining kinetic data characterizing physical exercise intensity of the physical exercise performed by the user; detecting that a measured cardiac output power exceeds a first threshold or that physical exercise intensity changes according to a rate exceeding a second threshold; upon the detecting, determining a synthetic cardiac output power parameter based at least partly on the kinetic data; and outputting the synthetic cardiac output power parameter.

Abstract: A wristband, an electronics module, and a wrist device are disclosed. The wristband and the electronics module form the modular wrist device. The electronics module, when mounted to the wristband, stiffens a structure of at least a portion of the wrist device in order to enable the wrist device to firmly attach against a wrist of a user and to enable optical heart activity measurement by the electronics module.

Abstract: A wristband, an electronics module, and a wrist device are disclosed. The wristband and the electronics module form the modular wrist device. The electronics module, when mounted to the wristband, stiffens a structure of at least a portion of the wrist device in order to enable the wrist device to firmly attach against a wrist of a user and to enable optical heart activity measurement by the electronics module.

Abstract: Performance intensity zones are disclosed. An apparatus comprises one or more processors, and one or more memories storing instructions, that, when executed by the one or more processors, cause the apparatus to: obtain performance intensity data measured from a user with at least one measurement sensor during a first activity and/or a second activity; and classify the performance intensity data in relation to a plurality of predetermined performance intensity zones, wherein each performance intensity zone is predetermined by a first numerical range for the first activity, and a second numerical range for the second activity, wherein the first activity and the second activity are different types of sports or different types of physical activities.