SupplementaryTable4_Methodological heterogeneity biases physical activity metrics derived from the Actigraph GT3X in multiple sclerosis: A rapid review and comparative study.xlsx

BackgroundPhysical activity (PA) is reduced in persons with multiple sclerosis (MS), though it is known to aid in symptom and fatigue management. Methods for measuring PA are diverse and the impact of this heterogeneity on study outcomes is unclear. We aimed to clarify this impact by comparing common methods for deriving PA metrics in MS populations.
MethodsFirst, a rapid review of existing literature identified methods for calculating PA in studies which used the Actigraph GT3X in populations with MS. We then compared methods in a prospective study on 42 persons with MS [EDSS 4.5 (3.5–6)] during a voluntary course of inpatient neurorehabilitation. Mixed-effects linear regression identified methodological factors which influenced PA measurements. Non-parametric hypothesis tests, correlations, and agreement statistics assessed overall and pairwise differences between methods.
ResultsIn the rapid review, searches identified 421 unique records. Sixty-nine records representing 51 eligible studies exhibited substantial heterogeneity in methodology and reporting practices. In a subsequent comparative study, multiple methods for deriving six PA metrics (step count, activity counts, total time in PA, sedentary time, time in light PA, time in moderate to vigorous PA), were identified and directly compared. All metrics were sensitive to methodological factors such as the selected preprocessing filter, data source (vertical vs. vector magnitude counts), and cutpoint. Additionally, sedentary time was sensitive to wear time definitions. Pairwise correlation and agreement between methods varied from weak (minimum correlation: 0.15, minimum agreement: 0.03) to perfect (maximum correlation: 1.00, maximum agreement: 1.00). Methodological factors biased both point estimates of PA and correlations between PA and clinical assessments.
ConclusionsMethodological heterogeneity of existing literature is high, and this heterogeneity may confound studies which use the Actigraph GT3X. Step counts were highly sensitive to the filter used to process raw accelerometer data. Sedentary time was particularly sensitive to methodology, and we recommend using total time in PA instead. Several, though not all, methods for deriving light PA and moderate to vigorous PA yielded nearly identical results. PA metrics based on vertical axis counts tended to outperform those based on vector magnitude counts. Additional research is needed to establish the relative validity of existing methods.

研究背景：身体活动（Physical Activity, PA）在多发性硬化（Multiple Sclerosis, MS）患者中普遍降低，但已有研究证实其有助于缓解症状与疲劳。当前身体活动的测量方法多种多样，且这种方法异质性对研究结果的影响尚不明确。本研究旨在通过对比多发性硬化人群中常用的身体活动指标推导方法，阐明该异质性的影响。

研究方法：首先，本研究通过快速回顾现有文献，梳理了在多发性硬化人群中使用Actigraph GT3X设备开展的身体活动测量研究中的计算方法。随后，本研究针对42名多发性硬化患者[扩展残疾状态量表（Expanded Disability Status Scale, EDSS）评分4.5（3.5~6）]在自愿参与的住院神经康复疗程中的数据，对上述方法进行了对比分析。采用混合效应线性回归模型，识别出影响身体活动测量结果的方法学因素；通过非参数假设检验、相关性分析及一致性统计量，评估了不同方法间的整体差异与两两差异。

研究结果：快速回顾阶段，检索共获得421条独立文献记录，其中69条记录对应51项符合纳入标准的研究，这些研究在方法学与报告规范上存在显著异质性。在后续的对比研究中，本研究共识别出6项身体活动指标[步数、活动计数、总身体活动时长、久坐时长、轻强度身体活动时长、中高强度身体活动时长]的多种推导方法，并进行了直接对比。所有指标均对方法学因素敏感，包括所选用的预处理滤波器、数据来源（垂直轴计数 vs 矢量模计数）以及截断阈值。此外，久坐时长对佩戴时长的定义十分敏感。不同方法间的两两相关性与一致性差异跨度较大，从弱相关（最低相关系数0.15，最低一致性系数0.03）到完全一致（最高相关系数1.00，最高一致性系数1.00）不等。方法学因素会对身体活动的点估计值，以及身体活动与临床评估指标间的相关性产生偏倚。

研究结论：现有文献的方法学异质性较高，该异质性可能会干扰使用Actigraph GT3X设备开展的研究结果。步数对用于处理原始加速度计数据的滤波器极为敏感。久坐时长对方法学尤为敏感，本研究建议采用总身体活动时长替代久坐时长作为指标。尽管并非全部，但多数用于推导轻强度与中高强度身体活动时长的方法可获得近乎一致的结果。基于垂直轴计数的身体活动指标往往优于基于矢量模计数的指标。未来仍需开展更多研究，以明确现有各类方法的相对有效性。