Table 1.

Inclusion and exclusion criteria.

	Chronic low back pain	Fibromyalgia	Pain-free controls
Inclusion	At least 3 months duration of low back pain	Pain in at least 4 of 5 regions Symptoms have been present at a similar level for at least 3 months Widespread pain index (WPI) ≥ 7 and symptom severity score (SSS) ≥ 5, or WPI of 4–6 and SSS score ≥ 9 The diagnosis is valid irrespective of other diagnoses
Exclusion	<18 years old Unable to provide informed consent to participate in the study or provide accurate data Unable to speak or write in the English language Currently have cancers or are undergoing treatment for cancer (except for skin cancers) Diagnosed with any non-skin cancer within the last 2 years Pregnant women by self-report	< 18 years old Unable to provide informed consent to participate in the study or provide accurate data Unable to speak or write in the English language Currently have cancers or are undergoing treatment for cancer (except for skin cancers) Diagnosed with any non-skin cancer within the last 2 years Pregnant women by self-report	< 18 years old Unable to provide informed consent to participate in the study or provide accurate data Unable to speak or write in the English language Currently have cancers or are undergoing treatment for cancer (except for skin cancers) Diagnosed with any non-skin cancer within the last 2 years Pregnant women by self-report Any continuous pain lasting > 1 day during the last two weeks Any pain at the time of the study procedures.