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

Background: The incremental shuttle walk test (ISWT) is a standardised assessment for cardiac rehabilitation. Three studies have reported oxygen costs (VO<inf>2</inf>)/metabolic equivalents (METs) of the ISWT. In spite of classic representations from these studies graphically showing curvilinear VO<inf>2</inf> responses to incremented walking speeds, linear regression techniques (also used by the American College of Sports Medicine [ACSM]) have been used to estimate VO<inf>2</inf>. Purpose: The two main aims of this study were to (i) resolve currently reported discrepancies in the ISWT VO<inf>2</inf>-walking speed relationship, and (ii) derive an appropriate VO<inf>2</inf> versus walking speed regression equation. Methods: VO<inf>2</inf> was measured continuously during an ISWT in 32 coronary heart disease [cardiac] rehabilitation (CHD-CR) participants and 30 age-matched controls. Results: Both CHD-CR and control group VO<inf>2</inf> responses were curvilinear in nature. For CHD-CR VO<inf>2</inf> = 4.4e^{0.23 × walkingspeed (km/h)}. The integrated area under the curve (iAUC) VO<inf>2</inf> 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. Conclusions: CHD-CR group vs. control VO<inf>2</inf> was up to 30 % greater at higher ISWT stages. The curvilinear nature of VO<inf>2</inf> responses during the ISWT concur with classic studies reported over 100 years. VO<inf>2</inf> 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.