In total, we invited 140 FM patients for screening. Patients were diagnosed as having FM (as confirmed by physician and medical records) and met the 2011 American College of Rheumatology criteria, which require the presence of widespread pain as well as a number of other somatic (e.g., sleep disturbance, fatigue), psychological (e.g., depression, anxiety) and cognitive symptoms .
After screening the 140 FM patients, 107 participants met the inclusion and exclusion criteria described below. This study was approved by the Partners Human Research Committee, and written informed consent was obtained from all participants. Participants were screened for the following criteria. The inclusion criteria were as follows: (1) 18–75 years old, (2) female, (3) Wolfe et al.’s  research criteria for FM diagnosis for at least 1 year, (4) baseline pain intensity of at least 3/10 on average and pain report for at least 50 percent of days, and (5) fluent in English and able to provide written informed consent. The exclusion criteria included (1) comorbid acute pain condition or comorbid chronic pain condition that is rated by the subject as more painful than FM, (2) current use of stimulant medications, (3) pregnant or nursing, (4) any psychiatric disorder involving a history of psychosis (e.g. schizophrenia, severe personality disorders), (5) psychiatric hospitalization in the past 6 months, (6) current or recent use of illicit drugs, (7) active suicidal ideation, and (8) lower limb vascular surgery or current lower limb vascular dysfunction (as part of the assessment protocol, patients underwent sensory testing on the legs).
The baseline visit included the informed consent, completion of questionnaires, and confirmation of eligibility (described below). Sociodemographic information included date of birth, marital status, educational, current occupational status, duration of pain symptoms, and medical comorbidities (Table 1). In addition, participants were asked to complete daily diaries for 7 days using a Likert scale via the Research Electronic Data Capture (REDCap) assessing daily pain and negative cognitions on pain (e.g. catastrophizing). Four surveys were used to assess key study variables: (1) Revised Fibromyalgia Impact Questionnaire (FIQR), (2) Brief Pain Inventory (BPI), (3) Pain Catastrophizing Scale (PCS), Patient-Reported Outcomes Measurement Information System (PROMIS)-anxiety, PROMIS- depression.
FM pain and symptoms. In order to measure FM symptomatology, we used the FIQR  and the BPI . The FIQR is a 21-question measure with an 11-point numeric rating scale (NRS) of 0 to 10, with 10 being “worst.” The FIQR is divided into three subscales for scoring: (1) “function,” (2) “overall impact,” and (3) “symptoms,” as well as a total overall score to assess the total impact of FM symptoms on a patient’s life. The BPI is a 15-item measure, which includes two multi-item subscales that measure (1) pain intensity and (2) pain interference with daily activities; the BPI is well-validated in chronic pain and is frequently recommended as an outcome measure of pain severity and pain interference.
Emotional Distress- Anxiety and Depression: Participants completed the PROMIS anxiety and depression short forms, which are widely used and extensively validated [18, 19]. The anxiety subscale consists of 7 items that ask respondents about the frequency with which they experience emotions such as fear, stress, and anxiety (“never” to “always”). The depression subscale consists of 8 items in which respondents indicate the frequency with which they have experienced emotions such as worthlessness, hopelessness, and sadness (“never” to “always”). Higher scores indicate more severe symptoms of emotional distress.
Daily Pain Catastrophizing. Patients were asked to report their levels of catastrophizing (0 “not at all” to 4 “all the time”; same response scale as used in the PCS) once a day for a period of 7 days using a Likert scale via the Research Electronic Data Capture (REDCap). The Situational Catastrophizing Questionnaire (SCQ) is a six-question adaptation of the PCS (described above). It has been used by our group in other studies and has been described more fully by Edwards and his lab [20, 21]
Daily Physical activity. Patients were asked to report their levels of physical activity (0 “not at all” to 100 “all the time”) once a day for a period of 7 days using a Likert scale  via the Research Electronic Data Capture (REDCap).
Daily Fitbit Flex Step Counts (physical activity). The Fitbit Flex is a popular, relatively inexpensive, and widely available small wristband that tracks physical activity, including measures of the estimated number of steps per day. The Fitbit Flex provides a valid measure of physical activity [23-25]. The FitbitFlex wirelessly synchronizes data to a computer, tablet, or phone and provides participants with feedback through a user-friendly website. Patients in the study wore the Fitbit Flex for the week during which they completed daily diaries; Fitbit Flex data was downloaded and stored at the end of the week. Participants optionally kept their Fitbit Flex after completion of the study. These data were used as part of an exploratory analysis to explore whether objective and subjective measures of physical activity are correlated.
BMI (Body Mass Index). The BMI was calculated according to the following formula BMI = body mass [kg] / (height [m]) 2.
All analyses were conducted using IBM-SPSS v.24. Descriptive data for continuous variables are presented as means and standard deviations (SDs), and data for categorical variables are presented as percentages (see Table 1).
Statistical assumptions and Pearson’s correlation coefficients were analyzed using SPSS (v. 23; IBM Corporation, Armonk NY) for MacVR. We conducted both bivariate correlations, controlling for age and education level, and the significance of associations did not differ. Thus, we will only report bivariate correlations.
To test our moderation model, we used the SPSS PROCESS macro, as it allows to test moderation effects . We tested Model 1, in which daily physical activity was the predictor, pain intensity (BPI) the dependent variable, daily pain catastrophizing was the moderator of the relationship between physical activity and pain intensity controlling for FM symptoms (FIQR) and Body Mass Index (BMI).