REF-713 · Bruinvels, Goldsmith, Blagrove, Simpkin, Lewis, Morton, Suppiah, Rogers, Ackerman, Newell & Pedlar, 2021 · British Journal of Sports Medicine, 2021;55 · Paper · PubMed
In 6812 exercising women, a higher menstrual-symptom burden was associated with missing or changing training: ask what she feels, not only where she is in the cycle
Protocol
Online 39-part survey of n=6812 adult exercising women of reproductive age (mean age 38.3 ± 8.7 years) who were not using combined hormonal contraception, recruited through the Strava exercise app user database in seven geographical areas (Brazil n=892, France n=1355, Germany n=839, Spain n=834, UK and Ireland n=1350, USA n=1542; questions translated and localised).
Respondents reported the presence and frequency of 18 commonly reported menstrual-cycle symptoms, from which the authors proposed a Menstrual Symptom index (MSi), range 0-54 (54 = all 18 symptoms occurring very frequently).
The MSi was tested against self-reported outcomes: missing or changing training, missing a sporting event/competition, absenteeism from work/academia, and use of pain medication, controlling for body mass index, training volume and age.
Key Findings
Symptom prevalence among the 6812 respondents:
| Symptom | Reported by |
|---|---|
| Mood changes / anxiety | 90.6% |
| Tiredness / fatigue | 86.2% |
| Stomach cramps | 84.2% |
| Breast pain / tenderness | 83.1% |
A higher MSi was associated with a greater likelihood of missing or changing training (OR 1.09, CI 1.08-1.10), missing a sporting event/competition (OR 1.07, CI 1.06-1.08), absenteeism from work/academia (OR 1.08, CI 1.07-1.09) and use of pain medication (OR 1.09, CI 1.08-1.09), after controlling for BMI, training volume and age. The odds ratios are per MSi point.
Authors' conclusion: symptoms are very common in exercising women, and women report that they compromise exercise participation and work capacity.
Inference, not tested: prevalence is near-universal while the index varies between women, which is why a graded score rather than a yes/no question is the useful measure.
Practical Application
In 6812 exercising women not on combined hormonal contraception, mood changes/anxiety (90.6%), tiredness (86.2%), cramps (84.2%) and breast pain (83.1%) were the most common cycle symptoms, and a higher symptom index was associated with missing or changing training (OR 1.09 per index point) and missing competitions (OR 1.07). Ask about symptoms and their frequency, not only about cycle phase.
The phase question itself is weak: a meta-analysis found only a trivial, inconsistent group-level effect of cycle phase on performance (REF-335); REF-571 reaches the same conclusion for resistance training. What this survey links to lost or changed sessions is symptom burden, and it can be asked about per athlete.
The most prevalent symptom is mood/anxiety (90.6%), not cramps. A drop in motivation or a spike in perceived effort around the cycle is common, not an outlier — do not read it as poor discipline.
Not from this paper; the base's own practice: log a simple symptom severity score alongside the usual readiness inputs and act on the score, not the calendar date. Treat missed sessions around menstruation as a load-continuity problem with a nameable cause. If symptoms are severe or escalating, that is a medical referral (heavy bleeding — see REF-573; missed cycles — see REF-341), not a coaching adjustment.
Limitations
Self-reported cross-sectional survey — association, not causation. No hormone verification of cycle phase or symptom timing.
Self-selected sample recruited through the Strava app, which skews toward motivated, technology-engaged and relatively active women; prevalence figures should not be read as population estimates.
The MSi was newly proposed and, as the authors state, needs formal psychometric validation. Treat the index as a practical prompt, not a validated instrument.
Women using combined hormonal contraception were not included, so the findings do not describe them.
Recall bias in symptom reporting; gynaecological conditions not controlled.
Symptom management itself is a clinical matter — persistent, severe or worsening symptoms warrant referral to a physician rather than a coaching workaround.
How this entry was checked and changed
Content correction 2026-09-27
Title said the study showed symptom burden "not cycle phase" removes training days -> the survey did not measure phase; it found the symptom index associated with missing or changing training. Phase point now attributed to REF-335.
Removed the invented "a rider losing 2-4 days a month" figure; added the abstract's odds ratios, mean age, regional n and the exclusion of combined hormonal contraception users.
Limitation "contraceptive use not fully controlled" -> combined hormonal contraception users were excluded by design.
Monitoring advice relabelled as the base's own practice.