Characteristics of the participants at baseline.

VO2 max is a measure of cardiorespiratory fitness and a key indicator of overall health. It is predictive of cardiovascular events and shows a strong inverse association with all-cause mortality. Increased cardiorespiratory fitness is associated with reductions in coronary artery disease, diabetes and cancer. Apple Watch offers a less resource-intensive and more feasible alternative to the gold standard assessment for VO2 max, indirect calorimetry, but the accuracy of its measurements remains uncertain. This study aimed to assess the validity of VO2 max estimates from Apple Watch in comparison to indirect calorimetry. Thirty participants wore an Apple Watch for 5-10 days to generate a VO2 max estimate. Subsequently, they underwent a maximal exercise treadmill test in accordance with the modified Åstrand protocol. The agreement between measurements from Apple Watch and indirect calorimetry was assessed using Bland-Altman analysis, mean absolute percentage error (MAPE), and mean absolute error (MAE). Overall, Apple Watch underestimated VO2 max, with a mean difference of 6.07 mL/kg/min (95% CI 3.77–8.38). Limits of agreement indicated variability between measurement methods (lower -6.11 mL/kg/min; upper 18.26 mL/kg/min). MAPE was calculated as 13.31% (95% CI 10.01–16.61), and MAE was 6.92 mL/kg/min (95% CI 4.89–8.94). These findings indicate that Apple Watch VO2 max estimates require further refinement prior to clinical implementation. However, further consideration of Apple Watch as an alternative to conventional VO2 max prediction from submaximal exercise is warranted, given its practical utility.

最大摄氧量（VO2 max）是衡量心肺适能的指标，亦是整体健康状况的关键指征。其可预测心血管不良事件的发生风险，且与全因死亡率呈显著负相关。心肺适能提升与冠状动脉疾病、糖尿病及癌症的发病风险降低密切相关。苹果手表（Apple Watch）为金标准检测方法——间接测热法（indirect calorimetry）——提供了一种资源消耗更低、实操性更强的替代方案，但其测量准确性尚未明确。本研究旨在评估苹果手表估算的最大摄氧量与间接测热法的一致性效度。30名参与者佩戴苹果手表5至10天以生成最大摄氧量估算值，随后依照改良Åstrand方案完成最大负荷跑台运动试验。研究采用Bland-Altman分析、平均绝对百分比误差（mean absolute percentage error，MAPE）与平均绝对误差（mean absolute error，MAE），评估苹果手表与间接测热法测量结果的一致性。整体而言，苹果手表对最大摄氧量的估算值偏低，平均差值为6.07 mL/kg/min（95%置信区间3.77–8.38）。一致性界限显示两种测量方法间存在变异（下限-6.11 mL/kg/min；上限18.26 mL/kg/min）。MAPE计算值为13.31%（95%置信区间10.01–16.61），MAE为6.92 mL/kg/min（95%置信区间4.89–8.94）。本研究结果表明，苹果手表的最大摄氧量估算值在应用于临床场景前仍需进一步优化。不过，鉴于其实际应用价值，仍有必要进一步探讨将苹果手表作为亚极量运动衍生的传统最大摄氧量预测方法替代方案的可行性。