Oxygen Costs of the Incremental Shuttle Walk Test in Cardiac Rehabilitation Participants: An Historical and Contemporary Analysis.

Abstract

The incremental shuttle walk test (ISWT) is a standardised assessment for cardiac rehabilitation. Three studies have reported oxygen costs (VO₂)/metabolic equivalents (METs) of the ISWT. In spite of classic representations from these studies graphically showing curvilinear VO₂ responses to incremented walking speeds, linear regression techniques (also used by the American College of Sports Medicine [ACSM]) have been used to estimate VO₂. The two main aims of this study were to (i) resolve currently reported discrepancies in the ISWT VO₂-walking speed relationship, and (ii) derive an appropriate VO₂ versus walking speed regression equation. VO₂ was measured continuously during an ISWT in 32 coronary heart disease [cardiac] rehabilitation (CHD-CR) participants and 30 age-matched controls. Both CHD-CR and control group VO₂ responses were curvilinear in nature. For CHD-CR VO₂ = 4.4e^{0.23 × walkingspeed (km/h)}. The integrated area under the curve (iAUC) VO₂ across nine ISWT stages was greater in the CHD-CR group versus the control group (p < 0.001): CHD-CR = 423 (±86) ml·kg^-1·min^-1·km·h^-1; control = 316 (±52) ml·kg^-1·min^-1·km·h^-1. CHD-CR group vs. control VO₂ was up to 30 % greater at higher ISWT stages. The curvilinear nature of VO₂ responses during the ISWT concur with classic studies reported over 100 years. VO₂ estimates for walking using linear regression models (including the ACSM) clearly underestimate values in healthy and CHD-CR participants, and this study provides a resolution to this when the ISWT is used for CHD-CR populations.