Validity of a customized submaximal treadmill protocol for determining VO_2max

Introduction: A customized submaximal exercise test for cycle ergometry was reported as a superior estimate of maximum oxygen uptake (VO_2max) in comparison to the traditional YMCA ergometry test. Purpose: Following similar methodology, we sought to validate a customized submaximal treadmill test (CustomTM) compared with the widely used Bruce submaximal protocol. Methods: Participants (29 women and 21 men; age = 31.37 ± 11.44 year, BMI = 24.02 ± 3.03) performed a graded exercise test (GXT) with a subsequent exhaustive, square-wave bout for the verification of “true” VO_2max. In counterbalanced order, subjects then completed submaximal protocols. The CustomTM protocol consisted of two 3-min stages estimated at 35 and 70% of VO_2max, where VO_2max was estimated with a linear regression equation utilizing sex, BMI, age, and self-reported physical activity. Results: VO₂ values from the GXT and verification bout were 47.2 ± 7.7 and 47.0 ± 7.7 ml kg⁻¹ min⁻¹, respectively (ICC = 0.99, CV = 2.0%, TE = 0.83 ml kg⁻¹ min⁻¹), with the highest value used as “true” VO_2max (47.7 ± 7.7 ml kg⁻¹ min⁻¹). Neither the Bruce (45.95 ± 6.97 ml kg⁻¹ min⁻¹) nor the CustomTM (47.3 ± 9.4 ml kg⁻¹ min⁻¹) protocol differed from “true” VO_2max. The CustomTM had a “very large” measurement agreement with “true” VO_2max (ICC = 0.78, CV of 9.1%, TE = 4.07 ml kg⁻¹ min⁻¹). Bruce had a “large” measurement agreement with “true” VO_2max (ICC = 0.62, CV of 10.0%, TE = 4.51 ml kg⁻¹ min⁻¹). Conclusion: The CustomTM was superior to the Bruce protocol, because it included a stage below and above gas exchange threshold, yielded a better measurement agreement for “true” VO_2max, and was more time efficient.