Guest blog by Kirsty Elliott-Sale
There are many female athletes who have questions about the role of the menstrual cycle in their performance (1). During the menstrual cycle, there are changes in the amount of two important hormones, oestrogen and progesterone. A ‘perfect’ menstrual cycle lasts 28 days and is commonly divided into three phases (2): (i) during the first phase (called the early follicular phase), oestrogen and progesterone levels are low; (ii) in the middle phase (called the ovulatory phase), oestrogen levels are high and progesterone levels are low; and (iii) in the final phase (called the mid-luteal phase), oestrogen and progesterone levels are high.
Is performance affected by menstrual cycle phase?
These short-term, rapid changes in hormone levels might affect exercise performance, but right now the information on this topic is inconsistent and researchers haven’t yet agreed on whether exercise performance is affected by menstrual cycle phase. In our recent paper, we investigated whether the changes in hormone levels caused by the different menstrual cycle phases affects exercise performance by finding and analysing previous studies on this topic (3). As part of our analysis, we compared exercise performance during the early follicular phase with all other phases of the cycle. We also examined the quality of the studies we identified, so we could rate our confidence in the evidence; i.e., low quality studies provide low quality evidence, giving us a lesser degree of confidence in the findings and vice versa.
Our investigation uncovered 78 studies that were relevant to our questions and all together these studies included data from 1193 participants. It is important to realise though that a large proportion (42%) of these studies fell into the "low quality of evidence" category. The results from our investigation show that exercise performance might be trivially reduced during the early follicular phase of the menstrual cycle, compared to all other phases. The size of the effect is based on a scale starting with trivial, followed by small, then medium, then large, meaning that the effect of the early follicular phase on exercise performance is less than small. This means that exercise performance might be slightly reduced in some sportswomen when the amount of natural oestrogen and progesterone is low, usually during days 1-5 of the menstrual cycle, with day 1 being the first day of menstrual bleeding.
The results from our investigation show that exercise performance might be trivially reduced during the early follicular phase of the menstrual cycle, compared to all other phases.
It is important to understand that the effect of the menstrual cycle phase on performance was very variable between studies, making it difficult form a consistent conclusion. When you add the small size of the effect, the inconsistency between studies and the poor quality of the research, general guidelines on exercise performance across the menstrual cycle cannot, and should not, be formed. Instead, we recommend that a personalised approach should be taken based on each athlete’s individual response to exercise performance across the menstrual cycle.
Take home message on menstrual cycle and performance
Our overall take-home message is that although exercise performance was trivially reduced (slightly poorer) during the early follicular phase of the menstrual cycle compared with the other phases, the effects are likely to be so small as to be meaningless for most sportswomen. It is worth noting that these tiny effects might have relevance to elite athletes where the difference between winning and losing is marginal. So we recommend that practitioners working with elite sportswomen need to track and consider the menstrual cycle, and be aware of the potential times during the cycle when exercise performance might be reduced (early follicular phase) or enhanced (all other MC phases). We suggest that this approach should be tailored to, and informed by, the individual athlete, so we are working on a case by case basis.