“…Resting heart rate, walking heart rate and velocity are used to calculate either the Energy Efficiency Index (EEI) [2] or the Physiological Cost Index (PCI) [3]. These indexes are considered reasonable alternatives to direct measurement because of the linear relationship established between heart rate and oxygen consumption at submaximal workloads [4]. In addition, the assessment of heart rate can be performed with minimal equipment and expertise making this methodology easily applicable in a clinical setting.…”