Barbell Medicine - From Bench to Bedside

In the third installment of this series, we’ll review the data on how the menstrual cycle affects training and sports performance. If you’re new to this series, check out Part I and II, available here and here

Data on the Effects of the Menstrual Cycle on Performance

The main question is how these menstrual cycle impacts training adaptations and performance. A range of research has been conducted on the effects of the different phases of the menstrual cycle on sports performance as well women’s self-reported evaluation of their own performance. A brief review about phases of the menstrual cycle:

  • Follicular Phase: Usually takes place on days 0-14. Begins with shedding of endometrium (menses). Estrogen levels rise gradually throughout this phase, whereas progesterone is low. Body temperature tends to be lower during this phase as well.
  • Luteal Phase: Usually takes place on days ~14-28. Begins with luteinizing hormone (LH) surge and subsequent ovulation.  Progesterone levels rise through the middle of this phase, then drop. Estrogen levels decrease slightly from LH surge, but are maintained until end of phase, which is marked by the onset of the next menses. Body temperature tends to be higher during this phase as well.
  • Average menstrual cycle lasts 28-35 days with 14-21 days in the follicular phase and 14 days in the luteal phase.

Now, let’s take a look at the data

Research by Kishali et al. asked women how they felt during training and competition for 4 sports (Judoka, Taek-wondo, Volleyball, and Basketball). The researchers asked if women took home a medal, what level the athletes competed at, how disruptive athletes’ menstrual cycles were, and how they felt about their performance across the cycle. In this study, women medaled regardless of their menstrual cycle phase and there were no significant differences in performance despite athletes reporting feeling significantly better during the first 14 days of their cycle compared to the second 14 days. Kishali et al., 2006.

A 1996 study set out to test if estrogen affected muscle strength by measuring force production during the follicular phase when estrogen is at its highest. The researchers tested strength in the following groups:

  • untrained women not on birth control (12)
  • trained women not on birth control (10)
  • trained women on birth control (5)
  • untrained men (6)

The researchers tested strength by having the subjects smash a transducer as hard as they could between their thumb and index finger at various times during their menstrual cycle. Researchers determined the phase of the menstrual cycle based on the basal body temperature and urine LH test kits. Both trained and untrained women exhibited increases of about 10% from the beginning to the end the follicular phase. Blood plasma estrogen levels were measured in the trained groups, e.g. those taking birth control and those who weren’t, and there were no correlations between the estrogen levels and relative muscle force. Further, the strength performance varied between individuals in relation to the menstrual cycle, though these changes were relatively small in magnitude at ±1.2 lbs of force compared with the 24 lbs of force average. Phillips et al., 1996 c

 Another group of researchers measured strength performance, this time in the middle of the cycle, e.g. right at ovulation. The researchers recruited 20 sedentary women; 10 taking oral contraceptives and 10 not taking oral contraceptives. Quadriceps strength and handgrip strength was tested weekly for the length of two menstrual cycles. Cycle phase was standardized based on the number of days since the start of menstruation using a 32 day cycle. Ovulation was predicted to be 14 days prior to menstruation, but was not directly measured. Quadriceps strength was tested using maximum voluntary isometric strength with electrical stimulation to ensure that each woman reached maximal activation. Quadriceps strength was significantly stronger during“mid cycle”, e.g. 12-18 days since the start of the cycle.  The significant difference was, at its greatest, 13.5 lbs (or 11.7 %) in untrained women from any point in the cycle to this mid cycle portion. 13.5 lbs in only quadriceps strength may seem like a lot, however the standard deviation within the sample was about 11.2 lbs indicating a high degree of intra-individual variability in strength. Of note, the electrical stimulation ensured that women can maximally engage their muscles during a contraction and that the central nervous system is not inhibiting muscle contraction during a certain phase due to fatigue. Sarwar et al., 1996.

Nevertheless, two out of the three studies reviewed so far suggest their may be a small impact of the cycle phase on strength performance, with strength peaking at the end of the  follicular phase as estrogen and LH are increasing. Is this right?

A 2003 study took blood samples from 7 women at the same time of day on day 2 (early follicular phase)  and day 21 (mid luteal phase) of their cycle to measure estradiol, progesterone and testosterone levels. Subjects had  maximal voluntary isometric force measured by smashing their thumb and index finger together (like Phillips study) on these days as well.  No significant differences in strength performance were observed despite relatively large variations in hormone levels, which suggests that strength performance is not directly tied to hormone concentrations. Elliott et al., 2003. Still, let’s not get too misty-eyed about tests on small hand muscles.

Researchers had 19 healthy women with regular menstrual cycles test isometric quadriceps strength with superimposed electrical stimulation, with isokinetic (constant speed) knee flexion and extension strength at multiple angles during different phases of the menstrual cycle. At each day of testing, blood samples were collected to obtain estrogen, progesterone, LH, and FSH levels. There were no differences in quadriceps strength or isokinetic knee flexion or extension strength across the different phases. Additionally, none of the performance metrics had any correlation with the concentrations of hormones. The superimposition of electrical stimulation with the isometric quadriceps strength test ensures maximal contraction of the muscle and removes central fatigue (fatigue moderated by the central nervous system instead of fatigue resulting from a lack of metabolic resources in the muscles) as a confounding variable. This allows for the direct evaluation of the effects of menstrual hormones on strength and indicates that strength changes that occasionally appear in training around the menstrual cycle are possibly occurring because of a different response. Janse De Jonge et al., 2001. Admittedly, this is a small sample size. However, the methods are well controlled and this is good evidence that training is not affected by serum hormone concentrations. 

Overall, these studies are only evaluating single muscle or single joint strength when powerlifting performance is dependent on whole body compound coordination and movement. Romero-Moraleda et al examined 13 female triathletes, none of whom were taking hormonal contraceptives. Each athlete completed 1-Repetition Maximum (1 RM) half squat testing on day one and then performed 3 testing days where 20% 40% 60% and 80% of 1 RM half squats were performed at maximal velocity. These testing days correlated with either early follicular, late follicular, or mid luteal phases of the menstrual cycle and the testing order was randomized. Menstrual cycle phase was determined through a combination of temperature, LH urine concentration, and menses. Hormone concentrations were not measured. Peak power, mean power, mean velocity and peak velocity did not differ across the phases of the menstrual cycle. Romero-Moraleda et al., 2019

A more recent study compared hormone levels to strength performance in  50 women (25 taking oral contraceptives (OC) and 25 who are not) during knee extension, knee flexion,  and grip strength. Estrogen and progesterone were collected before the early follicular phase, ovulatory phase, and the mid-luteal phase. The. researchers didn’t find any effect of hormone levels on strength performance, though strength levels were slightly higher in the follicular phase as compared to the luteal phase. Weidauer et al., 2020. The authors concluded that there may be a non-hormonally mediated cause of strength performance differences during different menstrual phases, though additional data is needed to support this hypothesis.

Other Factors Affecting Performance 

A number of other factors influencing performance have been identified while investigating the effect of the menstrual cycle on exercise.

For example, Birch et al.  examined maximal isometric lifting strength (MILS) of the deadlift at knee height of 10 untrained women. Each woman performed 3 lifts for 3 seconds each and the best one was recorded.  There was no differences in MILS between menstrual cycle phases, but there was a ~13 lb difference in strength performance between lifting at 6:00 AM and 6:00 PM.  This suggests that there is not an effect of menstrual cycle phase, but the time of day and may have a small impact on strength performance. Birch & Reilly, 2002. Diurnal variations in strength have been established previously, but are likely related to the time people habitually exercise. Vitale et al 2017 Rae et al 2015 Mood is also rarely discussed in research papers on the menstrual cycle but has a significant effect on training Beedie et al., 2000 and may play a role.

For barbell training and the menstrual cycle, the existing data is limited to proxies like single-muscle force output, half-squats, or similar.  There is no consensus for the actual differences in strength sport performance or training adaptations based on the phases of the menstrual cycle due to the lack of data.  A review of multiple sports show the variety of effects of responses to different phases of the menstrual cycle. Data towards the right side of the vertical line  favors increased performance during the early follicular phase, whereas data towards the left side of the line favors increased performance during other phases. McNulty et al., 2020

(Fig. 4: Forrest plot review multiple studies and the effect of menstrual cycle phase on training. The dotted vertical line indicates no effect and each individual horizontal lines represent a study. The width of each indicates a researcher is 95% confident the mean lies on that line. Larger lines indicate the mean has a larger range of possibilities. The last line on the bottom is the average. Because it is sitting close to the “favors other phases” side of the figure the conclusion drawn from the data is there is not a specific effect of the early follicular phase on training.)

Some of the studies described above do mention oral contraceptives and their effects. Overall, oral contraceptives have a complicated effect on the body because different kinds of oral contraceptives have different levels of hormones (typically progesterone) that make comparison between different pills difficult. Most of the studies seem to show no difference in strength outcomes between those who take hormonal birth control and those who don’t. The dulling of menstrual symptoms has been shown to result in some tolerance to training and a reason for training improvements. Knowles et al., 2019. A recent meta-analysis found that the oral contraceptives may slightly reduce exercise performance in women, but the effects on a group level are very small and the inter-individual variation is wide. Elliott-Sale et al., 2020 This suggests a need for individual management based on an athletes response to hormonal contraceptives. Ultimately, hormonal contraceptives are used for a handful of different conditions such as abnormal uterine bleeding, endometriosis, prevention of pregnancy etc. and one could argue that appropriately managing these have a larger impact on training success than the very small, if any, effect of hormonal contraceptives on exercise performance.  As always, this topic is to be discussed between you and your doctor. Remember a baby will be more impactful on your training than any birth control will be.

Throughout this section, we have shown a broad range of responses to strength training across the menstrual cycle. The data presented that do show a difference are not always of the highest quality, as variables are not uniformly measured between studies, don’t always measure actual hormonal variation, and are ultimately not difficult to interpret. Our original hypothesis was “There is no reliable difference in performance between the different phases of the menstrual cycle in strength sports.”

Going through all the evidence above, the data does not seem to overwhelmingly reject this hypothesis, though individual responses may vary.  Next week, we’ll tackle the last part of this series and look at the effects of training periodization according to the phases of the menstrual cycle to see if this style of training is beneficial. 

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