Why is this Review important?
Fibromyalgia is defined as a condition of generalized, chronic body pain lasting at least three months. Patients experience problems in physical functioning like fatigue, stiffness, widespread muscular tenderness, balance impairment, decreased energy, and sexual involvement and in perceptual sensitivity to touch, loud noises, bright lights, odors, and cold. They also might experience cognitive impairments (attention, memory) and psychological disorders (mood, sleep, anxiety, depression). All of these impairments might lead to a decline in quality of life, productivity loss, unemployment, and disability. 
Genetic factors may contribute to fibromyalgia following a triggering event, through a dysfunctional stress response of the hypothalamo-pituitary axis. Therefore, there is need for and emphasis on nonpharmacological individualized tailored therapy to play a role as a ‘first-line treatment.’
Flexibility exercise training, focused on increasing or maintaining the movement of major joints (shoulders, hips, knees, ankles, back, neck), postural stability, balance, range of motion, muscle strength, stiffness, general physical function, and psychological well-being might be useful for fibromyalgia patients.
Flexibility exercise training is studied with larger trials in fibromyalgia populations, and future treatment guidelines may discuss the possible benefits. As a result, it was essential to unscramble information available in literature in the Review.
What does this Review talk about?
The Review’s objective is to evaluate the benefits and harms of flexibility exercise training in adults with fibromyalgia (average age 48.6 years). Trials included here were conducted in seven countries. Since the fibromyalgia prevalence is 2.7% globally with a 3:1 female to male ratio, most of the studies (58.3%) included in this Review have only female participants.
Reviewers defined flexibility exercise training programs as involving complete range of motion targeting major muscle-tendon units. Exercise programs ranged from 4 to 20 weeks of training, 1 to 3 times a day, and each session ranged from 40 to 60 minutes. Each stretch (range of motion) was held for 6 to 60 seconds, but the intensity of stretches was not reported in most cases. The flexibility exercise training delivery mode was either supervised or unsupervised home-based.
Which studies were included in the Review?
Authors included 12 randomized control trials involving 743 people. The flexibility exercise training for fibromyalgia was compared to an untreated control group, land-based aerobic training, resistance training, or other interventions, but the main comparison was done between the flexibility exercise training and land-based aerobic training. In these 12 trials, published as of December 2017, major outcomes were health-related quality of life (HRQoL), pain intensity, stiffness, fatigue, and physical function. Major outcomes were self-reported by the participants and were expressed on a 0-to-100 scale [Fibromyalgia Impact Questionnaire (FIQ)], where higher scores indicated worse HRQoL.
Adverse events also were considered in the Review outcomes as withdrawal from treatment (dropout) and harms (like swelling or tendinitis), if reported in the study.  
Who will be interested in this Review?
Patients with fibromyalgia, loved ones/caregivers of patients with fibromyalgia, professionals dealing with fibromyalgia, professionals working with chronic-pain syndromes, general practitioners, and policymakers.
Key results of this Review
Flexibility exercise training resulted in little benefit at 8 to 20 weeks’ follow-up compared with land-based aerobic exercise training. But the quality of evidence was observed to be low to very low as it does not show significant improvement in health-related quality of life, pain, fatigue, or physical function. People who received flexibility exercise training rated fatigue as 4% better and stiffness as 30% better. But participants reported health-related quality of life as 4% worse and pain intensity as 5% worsened. Similarly, physical function was rated as 6% worse in the intervention group.
Safety aspects were unclear since withdrawal from treatment (dropout) was similar in both groups. Information on other harms was scarce; only one study reported that one participant had an ankle tendon swelling (tendinitis), but it was not clearly stated whether the tendinitis was due to the flexibility exercise training.
Authors’ conclusions
Very low evidence was observed for flexibility exercise training outcomes as better compared to aerobic training, and for all-cause withdrawals, it may lead to little or no difference. Uncertainty was observed for flexibility training’s long-term effects. Authors downgraded the evidence, due to the small number of trials and participants and the high risk of biases (selection, performance, detection). Flexibility exercise was presumed as well tolerated (safety as uncertain) with similar withdrawal rates across groups and scarce adverse events.
What next?
Authors recommended that future studies on the effects of flexible exercise training in fibromyalgia patients should: include methodologically calculated bigger sample size, precisely document patients’ characteristics, and report detailed information on both intervention and control treatments. All of this information in future studies will reveal the effects of flexibility exercise training that are most important for patients, clinicians, and policymakers.