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 (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. Purpose: 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. Methods: VO2 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 VO2 responses were curvilinear in nature. For CHD-CR VO2 = 4.4e0.23 × 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. Conclusions: 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.