title: The acute effect of maximal exercise on plasma beta-endorphin levels in fibromyalgia patients.
abstract: BACKGROUND
  This study aimed to investigate the effect of strenuous exercise on β-endorphine (β-END) level in fibromyalgia (FM) patients compared to healthy subjects.
  
  
  METHODS
  We enrolled 30 FM patients and 15 healthy individuals. All study participants underwent a treadmill exercise test using modified Bruce protocol (M.Bruce). The goal of the test was achieving at least 70% of the predicted maximal heart rate (HRMax). The serum levels of β-END were measured before and after the exercise program. Measurements were done while heart rate was at least 70% of its predicted maximum.
  
  
  RESULTS
  The mean ± the standard deviation (SD) of exercise duration in the FM and control groups were 24.26 ± 5.29 and 29.06 ± 3.26 minutes, respectively, indicating a shorter time to achieve the goal heart rate in FM patients (P< 0.003). Most FM patients attained 70% HRMax at lower stages (stage 2 and 3) of M.Bruce compared to the control group (70% versus 6.6%, respectively;P< 0.0001). Compared to healthy subjects, FM patients had lower serum β-END levels both in baseline and post-exercise status (Mean ± SD: 122.07 ± 28.56 µg/ml and 246.55 ± 29.57 µg/ml in the control group versus 90.12 ± 20.91 µg/ml and 179.80 ± 28.57 µg/ml in FM patients, respectively;P< 0.001).
  
  
  CONCLUSIONS
  We found that FM patients had lower levels of β-END in both basal and post-exercise status. Exercise increased serum the β-END level in both groups but the average increase in β-END in FM patients was significantly lower than in the control group.
authors.affiliation: Department of Rheumatology, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Bidari
authors.affiliation: Rheumatology Research Center, Razi Hospital, School of Medicine, Guilan University of Medical Sciences, Rasht, Iran.
authors.forename: Banafsheh
authors.initials: B
authors.lastname: Ghavidel-Parsa
authors.affiliation: Medical Laser Research Center, Iranian Center for Medical Laser (ICML), Academic Center for Education, Culture and Research (ACECR), Tehran, Iran.
authors.forename: Sahar
authors.initials: S
authors.lastname: Rajabi
authors.affiliation: Golestan Research Center of Gastroenterology and Hepatology, Golestan University of Medical Sciences, Gorgan, Iran.
authors.forename: Omid
authors.initials: O
authors.lastname: Sanaei
authors.affiliation: Medical Laser Research Center, Iranian Center for Medical Laser (ICML), Academic Center for Education, Culture and Research (ACECR), Tehran, Iran.
authors.forename: Mehrangiz
authors.initials: M
authors.lastname: Toutounchi
keywords: Beta-endorphin; Exercise; Fibromyalgia; Healthy subjects; Pain; Serum