The menstrual cycle and exercise
The menstrual cycle, due to alterations in ovarian hormones, can have a profound effect on the health, performance and emotional wellbeing of women. The things that probably first spring to mind are the negative effects of pre-menstrual tension, and how menstruation itself might result in a decrease in performance. However, it is not all doom and gloom. In fact, women may be at a distinct advantage at certain phases of their menstrual cycle in terms of being able to sustain a relatively high level of intense activity. Indeed, one of the reasons why it has been speculated that women could in the future outperform their male counterparts in certain ultra-distance events (Whipp and Ward, 1992) is because of these favourable changes that occur across the menstrual cycle.
Exercise to music class
If 20 women attend an exercise to music class – assuming that all of them have normal and regular menstrual cycles – it is probable that four of those women will be menstruating, four of them may be feeling the effects of pre-menstrual tension, and eight of them will have a raised core body temperature, swollen limbs and increased water retention due to elevated progesterone levels. It is, therefore, extremely important to be aware of the physiological and psychological changes that occur in women across the menstrual cycle, so that the training regime or the activity levels can be adapted.
Phases of the menstrual cycle
Figure 1 shows changes in hormones that occur across the menstrual cycle. The first part of the menstrual cycle (day 1 to 14 in a 28-day cycle) is termed the follicular phase, since it reflects the growth of the follicle in the ovary. Oestrogen is secreted in increasing amounts as the follicle grows. The follicular phase ends when the follicle ruptures, releasing an ovum. This is termed ovulation and usually occurs around the 14th day. Ovulation can be detected using a urine test kit, which measures the surge in luteinising hormone (LH) (Figure 1), or by keeping temperature records, since body temperature usually peaks at this time.
The second phase of the menstrual cycle is the luteal phase, which usually runs from day 14 to day 28. Both oestrogen and progesterone increase and remain elevated throughout the luteal phase until either the ovum is fertilised, or menstruation occurs. The oral contraceptive pill, as a result of synthetic oestrogens and progesterone, simulates pregnancy (when oestrogen and progesterone are produced continuously by the placenta). Ovarian follicles do not develop and ovulation does not occur.
Physiological effects
The most noticeable physiological changes that occur throughout the menstrual cycle are increases in body temperature, body weight and ventilation. A higher core temperature is associated with the luteal phase (second part) of the menstrual cycle owing to the thermogenic effect of progesterone (Cagnacci et al, 1996). Practically, this may mean that when women exercise during this phase, they are less effective at dissipating heat. There is usually a delay in their sweating response, a decrease in blood flow to the skin, and a reduction in vasodilation of the capillaries. Women may, therefore, be at greater risk of overheating, especially when exercise takes place in a hot environment or in a non-air-conditioned or non-ventilated area. Because of this increase in core body temperature during the luteal phase, it is also likely that heart rate at rest and during exercise may be elevated. This should be recognised, especially if heart rate is used to monitor exercise intensity, to assess recovery, or to predict exercise capacity or O2max.
Increases in body weight
Increases in body weight are also common, particularly in the pre-menstrual phase, due to water retention, alterations in electrolyte balance and glycogen storage (Reilly, 2000). This may mean that women feel more bloated during this time, may complain of lethargy during exercise, or may have swollen limbs. Increases in body weight may also be disadvantageous to women competing in events where the weight is not supported, such as in running. An increase in ventilation has also been observed in the mid-luteal phase of the menstrual cycle, thought to be a result of the increase in progesterone (Williams and Krahenbuhl, 1997). Breathing rate usually increases, and women report feeling breathless.
Better performance
On a more positive side, it has been suggested by some researchers that women perform better in endurance activities in their luteal phase of the menstrual cycle, since they are able to increase fat mobilisation and breakdown, and inhibit the use of glycogen (eg, Jurkowski-Hall et al, 1981). Less lactate builds up in the muscle and, as a consequence, women are able to sustain a relatively high intensity of exercise for longer. Generally, women also report that they feel the exercise to be easier at this time (Hackney et al, 1991).
All these changes are a result of increases in the hormone oestrogen, and they have important implications for performance. When competing, for instance, a personal best might be achieved more easily in the second phase of the menstrual cycle. Performance in the first phase of the menstrual cycle may be at a relative low, and training may need to be adapted.
Several studies, in contrast to the above, have found no significant differences in substrate use during exercise between the luteal and follicular phases, nor in the individual’s ability to sustain exercise easily (eg, De Bruyn-Prevost et al, 1984). It could be that differences might only be observed in a glycogen-depleted state, either as a result of diet or prolonged exercise. In athletes maintaining a relatively high carbohydrate diet, significant menstrual cycle phase differences in performance have not been observed (Berend et al, 1994).
Another contention is that fluctuations in substrate use and blood lactate concentration only occur in untrained females, whereas no phase-related differences have been reported in trained females. Hence, in general, it could be said that women perform better in endurance events in the second half of the menstrual cycle, although individual differences in fitness, training status, diet and hormonal response may mean that differences are insignificant or are not apparent in some women. Furthermore, the elevated performance during the latter part of the cycle may be offset by symptoms of pre-menstrual tension that some women experience which include, for instance, anxiety, nausea, irritability, bloatedness, weight gain and lack of concentration.
Depression of the immune system may be correlated with elevated levels of oestrogen and progesterone. It has, therefore been suggested (Daly and Ey, 1996), that women should avoid high training volumes and stress in the late luteal and early follicular phases of their menstrual cycle, since there is a greater risk of overtraining. Even though endurance performance might be improved in the latter part of the menstrual cycle, if the female athlete trains too much because they feel like they are able to, suppression in the immune system might lead to overtraining.
Luteinising hormone acts on the ovaries to produce androgens (mainly testosterone and androstenedione) and follicular-stimulating hormone (FSH) allows the ovaries to convert androgens into oestrogen (see Figure 1). Maximum testosterone occurs mid-cycle, coinciding with the LH surge. There is some suggestion that peaks in testosterone combined with oestrogen lead to increases in strength, and that strength training may be more effective in the middle of the cycle, although again, individuals have been found to differ.
The pill and its effects
The oral contraceptive pill is known to have both positive and negative health benefits. On the one hand, the positive health benefits include:
- decreased pain during menstruation
- decrease in ovarian, endometrial and possibly breast cancer
- reduced risk of ectopic pregnancy
- control over irregular periods
- regulation of iron in the diet, hence controlling anaemia
- control or regulation of symptoms of pre-menstrual tension
- reduction in the incidence of osteoporosis.
Similar to the effects of the second phase of the menstrual cycle, taking the pill might also lead to glycogen sparing and a greater utilisation of fat, meaning that endurance performance is prolonged. In addition, if a woman wants to compete in a particular performance, she might use the pill to manipulate the timing of her period. In contrast, the negative effects of taking the pill include:
- more frequent headaches
- water retention
- breast tenderness
- nausea
- weight gain
- hypertension
- cerebrovascular disease
- breast cancer.
These ailments may counteract the physiological benefits of taking the pill. Although the pill might improve aerobic performance, it could be a disadvantage for strength activity since androgens (testosterone) are suppressed.
Summary
Every woman is different. In the same woman, differences can even occur in hormonal concentration from month to month. However, if you are aware of the benefits and limitations that the menstrual cycle presents, then it could be possible to schedule physical activity according to individual needs. Very generally, increased intensity in strength training might be beneficial mid-cycle.
Scheduling of endurance events, including competitions and tests of personal bests, might be more appropriate for the second phase of the menstrual cycle. Ensuring that exercise takes place in a cool environment at all times, especially in the latter part of the menstrual cycle, would be wise. The fact that heart rate may be elevated in the latter part of the cycle, both at rest and during exercise, should be acknowledged.
Finally, you should have an appreciation of the emotional needs of women, as well as the physiological limitations. You should also be aware that a predisposition for overtraining is associated with pre-menstruation and menstruation.
Courtesy of Fitness Professionals UK
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