Objectives: To develop a new method of representing energy expenditure using heart rate and to determine its reproducibility compared with the criterion standard of oxygen cost.
Design: Repeated-measures design.
Setting: University gait analysis laboratory and gymnasium at 2 spinal injury units.
Participants: Twenty unimpaired adults and 17 subjects with spinal cord injury (SCI).
Interventions: Not applicable.
Main outcome measures: Heart rate and oxygen consumption were measured on 20 unimpaired adults walking under controlled steady-state and nonsteady-state conditions. New methods of estimating energy expenditure by using heart rate were compared with oxygen consumption, oxygen cost, and Physiological Cost Index (PCI). Nine subjects with SCI, walking with and without functional electric stimulation, were assessed to determine use of these new measures with this group. Sensitivity to change of the new measurement techniques was investigated in 10 subjects with SCI, comparing wheelchair pushing to walking.
Results: The Total Heart Beat Index (THBI) was developed as a new index, calculated by dividing the total heartbeats during activity by distance traveled. High repeatability was found under steady-state and nonsteady-state conditions (intraclass correlation coefficients,.893-.995). Sensitivity to change in activity level was also shown.
Conclusions: The THBI is a simple parameter to calculate from continuous heart rate data and provides a reproducible alternative to gas analysis and the PCI.