Abstract: We included a total of 12 trials with 854 women in the review, with 10 trials and 754 women in the meta-analysis. Nine of the 10 studies compared exercise with no treatment, and one study compared exercise with NSAIDs. No studies compared exercise with attention control or with the oral contraceptive pill. Studies used low-intensity exercise (stretching, core strengthening or yoga) or high-intensity exercise (Zumba or aerobic training); none of the included studies used resistance training.  Exercise versus no treatment Exercise may have a large effect on reducing menstrual pain intensity compared to no exercise (standard mean difference (SMD) -1.86, 95% confidence interval (CI) -2.06 to -1.66; 9 randomised controlled trials (RCTs), n = 632; I2= 91%; low-quality evidence). This SMD corresponds to a 25 mm reduction on a 100 mm visual analogue scale (VAS) and is likely to be clinically significant. We are uncertain if there is any difference in adverse event rates between exercise and no treatment. We are uncertain if exercise reduces overall menstrual symptoms (as measured by the Moos Menstrual Distress Questionnaire (MMDQ)), such as back pain or fatigue compared to no treatment (mean difference (MD) -33.16, 95% CI -40.45 to -25.87; 1 RCT, n = 120; very low-quality evidence), or improves mental quality of life (MD 4.40, 95% CI 1.59 to 7.21; 1 RCT, n = 55; very low-quality evidence) or physical quality of life (as measured by the 12-Item Short Form Health Survey (SF-12)) compared to no exercise (MD 3.40, 95% CI -1.68 to 8.48; 1 RCT, n = 55; very low-quality evidence) when compared to no treatment. No studies reported on any changes in restriction of daily life activities or on absence from work or school. Exercise versus NSAIDs We are uncertain if exercise, when compared with mefenamic acid, reduced menstrual pain intensity (MD -7.40, 95% CI -8.36 to -6.44; 1 RCT, n = 122; very low-quality evidence), use of rescue analgesic medication (risk ratio (RR) 1.77, 95% CI 1.21 to 2.60; 1 RCT, n = 122; very low-quality evidence) or absence from work or school (RR 1.00, 95% CI 0.49 to 2.03; 1 RCT, n = 122; very low-quality evidence). None of the included studies reported on adverse events, overall menstrual symptoms, restriction of daily life activities or quality of life. The current low-quality evidence suggests that exercise, performed for about 45 to 60 minutes each time, three times per week or more, regardless of intensity, may provide a clinically significant reduction in menstrual pain intensity of around 25 mm on a 100 mm VAS. All studies used exercise regularly throughout the month, with some studies asking women not to exercise during menstruation. Given the overall health benefits of exercise, and the relatively low risk of side effects reported in the general population, women may consider using exercise, either alone or in conjunction with other modalities, such as NSAIDs, to manage menstrual pain. It is unclear if the benefits of exercise persist after regular exercise has stopped or if they are similar in women over the age of 25. Further research is required, using validated outcome measures, adequate blinding and suitable comparator groups reflecting current best practice or accounting for the extra attention given during exercise.

Plain-language summary: We found 12 studies including 854 women that examined the effect of exercise in women with period pain. The evidence is current to August 2019. Two trials did not report data suitable to be included in the meta-analysis, so we included 10 trials with 754 women in our meta-analysis. Eleven trials compared exercise with no treatment and one compared exercise with NSAIDs. Exercise, whether low-intensity, such as yoga, or high-intensity, such as aerobics, may provide a large reduction in the intensity of period pain, compared to not doing anything. This reduction in pain was likely to be important to women with period pain as it is over twice the minimum amount of pain reduction we think is needed to notice a difference. Most studies asked women to exercise at least three times per week, for about 45 to 60 minutes of exercise each time. It is unclear if exercising less frequently, or for a shorter duration would have the same results. Exercise was performed regularly throughout the month, with some studies asking women not to perform exercise during the period itself. The evidence for the safety of exercise was not well reported and so we cannot draw any conclusions. Other outcomes, such as the effect on overall menstrual symptoms or overall quality of life, were not well reported and the evidence was of very low quality, so we cannot be sure if exercise has any effect on these outcomes. No studies reported on rates of being absent from work or school or on restrictions of daily life activities. There was not enough evidence to determine if there was any benefit of exercise when compared to NSAIDs, a class of medications (like ibuprofen) commonly used to treat period pain, on menstrual pain intensity, need for additional pain-relieving medication, or absence from work or school. No studies reported on quality of life or restriction of daily life activities The quality of the evidence was low to very low. The main limitations were imprecision due to small sample sizes (too few women in the study), inconsistency (studies gave very different results) and risk of bias related to blinding (where researchers or participants knew what treatment they were getting).