Only skimmed part of the paper -- how they measured PEM. Thought there are a couple of points worthwhile to discuss:
"All interviews were conducted bedside in the volunteer’s hospital room with one study team member observing, except for the 4-hour post-CPET interview, which was conducted via telephone due to the volunteer undergoing respiratory exchange measurements in a metabolic chamber."
"Each interview lasted 30–45 min and was recorded and transcribed. By performing an assessment before undergoing CPET, we established each volunteer’s pre-CPET level. We sought to fully understand symptoms following CPET and to ascertain perceptions of the changes in symptom severity between timepoints."
"To gauge the severity of PEM, we asked ME/CFS volunteers to compare their current PEM with an episode in their day-to-day life during which they had severe PEM. Although the specific triggering event was different for each person, using the benchmark of ‘severe PEM’ created an individualised standard that could be compared across participants."
"Participants chose memorable events such as weddings and graduations. These memorable events created an internal standard for comparison that was salient to each participant’s experiences. [...]"
"VAS data were collected for 12 symptoms immediately following the QI and at the same six timepoints: physical fatigue, mental fatigue or mental fog, muscle aches, joint aches, headache, muscle weakness, light headedness, flu-like symptoms, sore throat, gastrointestinal symptoms, shortness of breath and sensitive to environment."
"Volunteers were provided a tablet and instructed ‘to place an ‘X’ on a line for each symptom to indicate how they felt RIGHT NOW’. (figure 1). Lines were anchored on the left and right side indicating ‘NOT AT ALL’ and ‘MOST EXTREME’."
[I think there are some good considerations and some less good considerations in that part. For now, hghlighted only the ones I find problematic with regard to potentially dismissing PEM while trying to capture it.]