Step-rate cut-points for physical activity intensity in patients with multiple sclerosis: The effect of disability status

Background Evaluating the relationship between step-rate and rate of oxygen uptake (VO₂) may allow for practical physical activity assessment in patients with multiple sclerosis (MS) of differing disability levels. Aims To examine whether the VO₂ to step-rate relationship during over-ground walking differs across varying disability levels among patients with MS and to develop step-rate thresholds for moderate- and vigorous-intensity physical activity. Materials and methods Adults with MS (N = 58; age: 51 ± 9 years; 48 women) completed one over-ground walking trial at comfortable speed, one at 0.22 m·s^{- 1} slower, and one at 0.22 m·s^{- 1} faster. Each trial lasted 6 min. VO₂ was measured with portable spirometry and steps with hand-tally. Disability status was classified as mild, moderate, or severe based on Expanded Disability Status Scale scores. Results Multi-level regression indicated that step-rate, disability status, and height significantly predicted VO₂ (p < 0.05). Based on this model, we developed step-rate thresholds for activity intensity that vary by disability status and height. A separate regression without height allowed for development of step-rate thresholds that vary only by disability status. Conclusion The VO₂ during over-ground walking differs among ambulatory patients with MS based on disability level and height, yielding different step-rate thresholds for physical activity intensity.