Does the menstrual cycle have an effect on strength training?
Updated: Apr 24
The menstrual cycle is a hormonal process that a woman’s body goes through approximately every 28 days to prepare for pregnancy, however there is inter and intra time variation between women. The menses/menstruation is more commonly known as a period and is the phase when blood and tissue is discharged from uterus lining.
Historically testing the menstrual cycle in relationship to sports performance has been a grey area because it is a complex barrier that often means that women are left out of clinical trials. As a result of years of women not being included in medical studies, it is now known that women react differently to several drugs (1) . Recent findings have shown that women are twice as likely to have an adverse reaction to drugs than males.
However, as we learn more about the menstrual cycle and it becomes increasingly necessary to include women In clinical trials, it has become apparent that more needs to be done to clarify how to include the menstrual cycle when testing for performance.
The menstrual cycle is often divided into two sections, the follicular and luteal phase, with ovulation dividing them both. From here, the phases can be broken down into more sections, ranging from early, mid and late follicular and luteal phases. It is the different levels of the hormones oestrogen and progesterone and the way they interact with each other that is believed to obscure the known effects of the menstrual cycle on performance.
In terms of hormone levels, it is essential to know that generally, women have low oestrogen and progesterone in the early follicular phase with oestrogen rising and peaking in the late follicular phase. After ovulation, oestrogen rises again, however this is when progesterone peaks in the mid-luteal phase.
One of the reasons it is difficult to monitor the menstrual cycle in relation to strength training is due to the methods of verifying each cycle. Currently there several invasive and non-invasive methods, however many of them are not accurate enough to give a clear indication of which phase the female is in. Most verification methods focus on the occurrence of ovulation so they can divide the follicular and luteal phase. This avoids the inclusion of non-ovulatory and luteal phase deficiency (LPD) cycles. Both have low progesterone during the second half of the cycle. Women who suffer with anovulation and LPD may still bleed and not be aware they have this problem, therefore methods such as calendar tracking do not work for women with these conditions (2).
The only method that can identify the two phases is the measurement of both oestrogen and progesterone. The three phases being early follicular, late follicular and mid luteal. Some studies state ' follicular phase' but don't say whether it's easy , mid or late. Another issue with research on the menstrual cycle is that they all test different phases of the cycle. The follicular phase is varied in length compared to the luteal phase and so it can be difficult to predict the day of ovulation. Also, the length of the cycle varies each time.
It is expected that there will be variations in the hormone concentration between different phases. In the same phase there is also a lot of variability in the hormone concentrations between women (3). Also, with the same women, progesterone levels fluctuate greatly during the mid-luteal phase, of up to 64 nmol/L within several hours (4). This is due to the pulsatile secretion of the hormones. Progesterone is highest in the morning (4) so timing of the day should be taken into account when doing studies. Also, exercise increases both progesterone and oestrogen levels (4).
Another thing to note is how oestrogen and progesterone interact with each other. Although two women have the same oestrogen levels at a certain point in their cycles, they might have varying progesterone levels and so the effect of oestrogen may be different to each of them (3).
Despite the difficulty in testing whether the menstrual cycle has an effect on strength training, current literature suggests that fluctuation of hormones throughout the menstrual cycle do not affect muscle contractile characteristics. There are conflicting results regarding the connection between muscle contractile characteristics and the menstrual cycle. Sarwar et al (5) showed that women with a regular menstrual cycle were stronger between days 12-18 and Phillip et at (6) showed increased adductor pollicis strength during the follicular phase and decreased strength during ovulation.
However other studies (4) showed a negative relationship with oestrogen and handgrip strength and another (7) showed the most strength during the mid-luteal phase. Other studies have shown no connection between muscle contractile characteristics and menstrual cycle. In Sarwar's study the hormone concentration levels were not measured to match the phases and might have included non-ovulatory cycles. (7) that found low strength in the follicular and highest in luteal phase but did not indicate the progesterone concentration level that indicates ovulation.
Although these studies give quantitative evidence that muscular strength is not affected by the menstrual cycle, in terms of qualitative research, 41% of exercising women believe that their menstrual cycle has a negative impact on performance and training (8). Oestrogen rises halfway through the follicular phase and peaks just before ovulation. During the luteal phase oestrogen and progesterone are elevated, prog peaks. Research investigating large fluctuations in female hormones show that different levels of oestrogen and progesterone can cause changes in the thermoregulatory, respiratory and renal systems. This may all have an effect on exercise and performance.
On top of this, it is essential to take into account how the menstrual cycle makes women feel. Although strength might not be directly affected, many women report feeling fatigued during certain phases in their cycle, disorientated and also have menstrual cramps that may affect performance. Therefore, it is necessary to also take into account the qualitative research.
Going forward, in order to test whether the menstrual cycle truly has an effect on strength training, testing needs to be done during each phase of the cycle and compared, using women that do not suffer from any menstrual conditions such as anovulation of LPD. As well as this, other qualitative factors need to be taken into consideration such as feelings of fatigue and pain during different phases. However, as cycle vary in time and hormone levels so greatly between women and within their own cycles, it will take a long time before testing can become more accurate.