Validity and reproducibility of crutch force and heart rate measurements to assess energy expenditure of paraplegic gait

Objective: To determine the validity and reproducibility of heart rate (HR) and crutch force measurements to estimate energy expenditure during parapl egic walking. Usefulness of these outcome measures in comparative trials wa s assessed in terms of responsiveness. Design: Cross-sectional validity was determined using one single (first) me asurement. Longitudinal validity as well as reproducibility were calculated using repeated measurements. Setting: Oxygen uptake and HR during steady state as well as axial crutch l oad were measured at subjects' self-selected walking speeds. Patients: Ten subjects with thoracic-level spinal cord injury were included in the study. All subjects had considerable experience with ambulation in the advanced reciprocating gait orthosis (ARGO). Main Outcome Measures: Oxygen uptake ((V) over dot O-2, mL/min) and oxygen cost (EO2, mL/m) were used as criterion standards. Crutch peak force (CPF), crutch force time integral (CFTI), HR, and physiological cost index (PCI) were used to estimate energy expenditure. Results: The PCI was found to be sensitive to detect differences between se ssions in criterion standard (r = .86). Smallest detectable difference (ie, point where difference exceeds measurement error) ranged from approximatel y 15% for CPF to 33.7% and 41.8% for EO2 and PCI, respectively. Conclusions: Although PCI is expected to be a valid measure for within-pati ent differences in (V) over dot O-2, responsiveness was lower compared to E O2 and CPF. The limited number of patients who can be included in studies o n paraplegic locomotion requires reproducible outcome measures. Therefore, CPF and EO2 are advocated in favor of PCI. (C) 1999 by the American Congres s of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation.