The acute effect of maximal exercise on plasma beta-endorphin levels in fibromyalgia patients

Background: This study aimed to investigate the effect of strenuous exercise on ${\beta}$-endorphine (${\beta}$-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 ${\beta}$-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 ${\pm}$ the standard deviation (SD) of exercise duration in the FM and control groups were $24.26{\pm}5.29$ and $29.06{\pm}3.26$ 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 ${\beta}$-END levels both in baseline and post-exercise status ($Mean{\pm}SD$: $122.07{\pm}28.56{\mu}g/ml$ and $246.55{\pm}29.57{\mu}g/ml$ in the control group versus $90.12{\pm}20.91{\mu}g/ml$ and $179.80{\pm}28.57{\mu}g/ml$ in FM patients, respectively; P < 0.001). Conclusions: We found that FM patients had lower levels of ${\beta}$-END in both basal and post-exercise status. Exercise increased serum the ${\beta}$-END level in both groups but the average increase in ${\beta}$-END in FM patients was significantly lower than in the control group.