Objectives Inflammatory myopathies are characterized by muscle weakness that limits the activities of daily living. Daily step count is an accepted metric of physical activity. Wearable technologies such as Fitbit® enable tracking of daily step counts. We assessed the psychometric properties of Fitbit® and compared the accuracy of Fitbit® step counts to ActiGraph®. Methods This was a pilot, proof of concept, prospective observational study with four visits at 0, 1, 3 and 6 months in PM, DM, necrotizing myopathy (NM) or anti-synthetase syndrome (AS) subjects. Six core set measures (manual muscle testing, physician global disease activity, patient global disease activity, and extra-muscular disease activity, HAQ-Disability Index and creatine kinase), three functional tests (six-min walk, timed up-and-go, sit-to-stand tests) and SF-36 physical function-10 (PF10) were collected at each visit. Patients wore waist-worn Fitbit® One and ActiGraph® T3X-BT concurrently for 7 days/month for 6 months. Results Twenty-four (10 DM, 8 PM/NM, 6 AS) patients (17 females/7 males; 91% Caucasian) were enrolled. Test-retest reliability of daily steps was strong in 1-month follow-up (ICC 0.89). Daily steps and peak 1-min cadence showed moderate-strong correlations with physician global disease activity, patient global disease activity, HAQ-Disability Index, SF-36 PF10 and all three functional tests. Fitbit® and ActiGraph® step counts demonstrated good agreement and strong correlation (ICC 0.96). Conclusion Fitbit® daily steps and peak 1-min cadence are reliable and valid measures of physical activity in a cohort of myositis patients. This pilot data suggests that Fitbit® has a potential for use in clinical practice and trials to monitor physical activity in myositis patients, but larger studies are needed for further validation.

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基于消费者的活动跟踪器评估肌炎患者的身体活动

目标 炎症性肌病的特征是肌肉无力，限制了日常生活的活动。每日步数是公认的体育活动指标。Fitbit® 等可穿戴技术可以跟踪每日步数。我们评估了 Fitbit® 的心理测量特性，并将 Fitbit® 步数的准确性与 ActiGraph® 进行了比较。方法 这是一项试点、概念验证、前瞻性观察研究，在 0、1、3 和 6 个月对 PM、DM、坏死性肌病 (NM) 或抗合成酶综合征 (AS) 受试者进行了四次访问。六项核心组测量（手动肌肉测试、医生整体疾病活动、患者整体疾病活动和肌肉外疾病活动、HAQ 残疾指数和肌酸激酶）、三项功能测试（六分钟步行、定时起跑, 每次就诊时都收集了坐站测试）和 SF-36 身体功能 10（PF10）。患者同时佩戴腰部佩戴的 Fitbit® One 和 ActiGraph® T3X-BT 7 天/月，持续 6 个月。结果 24 名（10 名 DM，8 名 PM/NM，6 名 AS）患者（17 名女性/7 名男性；91% 白种人）被纳入研究。在 1 个月的随访中，每日步数的重测信度很高（ICC 0.89）。每日步数和峰值 1 分钟节奏与医生整体疾病活动、患者整体疾病活动、HAQ 残疾指数、SF-36 PF10 和所有三项功能测试显示出中强相关性。Fitbit® 和 ActiGraph® 步数显示出良好的一致性和强相关性 (ICC 0.96)。结论 Fitbit® 每日步数和峰值 1 分钟节奏是一组肌炎患者身体活动的可靠且有效的测量方法。