Measuring the heart rate (taking the pulse) is one the most useful ways of assessing the workload because it can be done so easily.
One can easily feel the pulses (the blood pressure in waves) at the radial artery in the wrist or at the carotid artery at the neck but to do this while a person is at work is an intrusion that may disturb his or her work, thereby producing a false result. Instruments have been devised which give a continuous record of heart rate during work. One kind uses the changes in tissue volume with each pulse: the most modern method uses the electrical current associated with the actions of the heart muscle (as can be seen in the electrocardiogram) and the heart rate is counted by the number of R peaks (the strongest action potential) per unit of time, usually per minute.