A system or a method for providing pacing guidance to an individual for a particular activity based on a physiological strain index (PSI) or an adaptive physiological strain index (aPSI). The system in at least one embodiment includes a heart rate monitor, a memory storing multiple pacing templates, a clock, an activity completion module, an output device, and a processor configured to perform multiple steps resulting in outputting pacing information to the individual. The pacing information selected in at least one embodiment is based on the individual's heart rate that provides in part a PSI or aPSI, the elapsed time for the activity, and the amount of progress through the activity.