Should We Stick with Step Counts after Incomplete Spinal Cord Injury? A Case-Control Investigation

Abstract

Step count is a common metric or criterion to prescribe physical activity. Step activity benchmarks were designed to reflect an overall daily energy expenditure, but this objective measure is exposed to error when gait is impaired. Individuals with functional limitations are known to expend more energy during locomotion when compared to non-impaired controls (CON). PURPOSE: The primary goal was to evaluate metabolic cost per step for someone with an incomplete spinal cord injury (iSCI) when compared to a CON. A secondary goal was to evaluate estimated daily energy expended between the individuals to determine if step count is an appropriate metric for activity recommendations for those with functional limitations. METHODS: This case-control study included a participant with an iSCI and an age-, sex-, height-matched CON. Participants completed a 6-minute walk (6MWT) and timed walks at slow, moderate, and fast paces (matching the step monitor’s intensity benchmarks) while wearing a portable metabolic cart. Relative oxygen consumption (VO2) was determined using a 15-breath moving average. Daily step activity was recorded during the 7-day period between sessions. Stride length was determined using 3D motion analysis. RESULTS: Differences were observed between participants for average 6MWT VO2 (iSCI=21.5 ml/kg/min; CON=28.18 ml/kg/min), step length (iSCI: 0.36m; CON: 0.73m), energy expenditure during the 6MWT (iSCI: 0.34kcal/m; CON: 0.09kcal/m), and daily step activity (iSCI: 2616, CON: 9890). Estimated energy expended from walking for iSCI and CON was 336 kcal/day and 735 kcal/day, respectively, when extrapolating VO2 from paced walks to data retrieved from the step monitor. CONCLUSION: Supporting previous literature, it is likely inappropriate to standardize activity recommendations based on step metrics for those with functional limitations. Unrealistic expectations may heighten perceived barriers, undermine mobility related self-efficacy, and discourage adoption or adherence. Exercise prescription based on energy expenditure goals may serve as an alternative means to individualize recommended daily activity. Future research should attempt to establish new recommendations based on functional status for those outside of the typical gate norm.