Quantifying cardiorespiratory responses resulting from speed and slope increments during motorized treadmill propulsion among manual wheelchair users

Abstract

Background: Cardiorespiratory fitness assessment and training among manual wheelchair (MW) users are predominantly done with an arm-crank ergometer. However, arm-crank ergometer biomechanics differ substantially from MW propulsion biomechanics. This study aimed to quantify cardiorespiratory responses resulting from speed and slope increments during MW propulsion on a motorized treadmill and to calculate a predictive equation based on speed and slope for estimating peak oxygen uptake (VO_2peak) in MW users.

Methods: In total, 17 long-term MW users completed 12 MW propulsion periods (PP), each lasting 2min, on a motorized treadmill, in a random order. Each PP was separated by a 2-min rest. PPs were characterized by a combination of 3 speeds (0.6, 0.8 and 1.0m/s) and 4 slopes (0°, 2.7°, 3.6° and 4.8°). Six key cardiorespiratory outcome measures (VO₂, heart rate, respiratory rate, minute ventilation and tidal volume) were recorded by using a gas-exchange analysis system. Rate of perceived exertion (RPE) was measured by using the modified 10-point Borg scale after each PP.

Results: For the 14 participants who completed the test, cardiorespiratory responses increased in response to speed and/or slope increments, except those recorded between the 3.6^o and 4.8^o slope, for which most outcome measures were comparable. The RPE was positively associated with cardiorespiratory response (r_s≥0.85). A VO₂ predictive equation (R²=99.7%) based on speed and slope for each PP was computed. This equation informed the development of a future testing protocol to linearly increase VO₂ via 1-min stages during treadmill MW propulsion.

Conclusions: Increasing speed and slope while propelling a MW on a motorized treadmill increases cardiorespiratory response along with RPE. RPE can be used to easily and accurately monitor cardiorespiratory responses during MW exercise. The VO₂ can be predicted to some extent by speed and slope during MW propulsion. A testing protocol is proposed to assess cardiorespiratory fitness during motorized MW propulsion.

Keywords: Cardiorespiratory fitness; Manual wheelchair users; Propulsion; Rehabilitation; Treadmill.