Saturday, 14 February 2015

The Menstrual Cycle and Performance

As a result of comments by tennis player Heather Watson, there has been some debate in the sports media recently as to whether or not periods affect performance.  As someone who suffered from period pain, and seemingly unexplained awful performances at 'the time of the month' in my younger days, I have no doubt but that they do. The research, however, may suggest otherwise, as I found when researching for my undergraduate project some 14 years ago.

Recent mainstream articles have indicated that there has been very little research in the area. Technically, that is not true.  The research, however, like much other research, may not be relevant in the high performance environment, and does not take into consideration the huge variation in menstrual symptoms between individuals.

The Menstrual Cycle and Hormone Fluctuations

The monthly cycles of ovum maturation, ovulation, endometrium thickening and menstrual flow are controlled by the interactions and fluctuations of a number of hormones. The ovarian hormones (oestrogen and progesterone); gonadrotropin-releasing hormone, secreted from the hypothalamus; the pituitary gonadrophic hormones (follicle stimulating hormone and luteinising hormone); and peptides (inhibin) all play an important role in the human menstrual cycle. The complicated interaction between these hormones involves both negative and positive feedback loops, and results in two main phases, each approximately two weeks in duration: the follicular phase (the time between the beginning of menses and ovulation), and the luteal phase (between ovulation and menses).


Menstrual hormones and physiological parameters

It is well know that the two main reproductive hormones - oestrogen and progesterone - affect muscle strength and bone health.  The steep decline in muscle strength (Greeves et al, 1999, Phillips et al, 1993a, Skelton et al, 1999) and bone mineral density that occurs during and after menopause reflects the sharp reduction in oestrogen and progesterone that occurs at this time. This has led investigators to question whether the much smaller fluctuations in oestrogen and progesterone that occur during the menstrual cycle have any effect on muscle strength performance or any other physiological parameter.

The results from subsequent studies - and there have been quite a few - are far from conclusive. Previous research has found increased muscle strength (Jacobson et al, 1998, Phillips et al, 1993b, Phillips et al, 1996) and increased heat tolerance (Tenaglia et al, 1999) during the follicular phase of the menstrual cycle. High progesterone levels characteristic of the luteal phase of the menstrual cycle are associated with decreased muscle coordination and increased susceptibility to injury (Moller-Nielse & Hammer, 1989), increased body temperature (Tenaglia et al, 1999), and reduced lactate production (Hall Jurkowski, 1981).  But not all research has found such variations.  Indeed a study of 80 females at the 1964 Tokyo Olympic Games indicated that gold medals were won during all phases of the menstrual cycle (Zaharieva, 1965).

Problems with the research

The current research may not be given the whole picture.  The factors which determine performance at the highest level are numerous and complex, and isolated studies on small groups of untrained females are unlikely to tell us much about what happens in an individual, highly trained athlete competing in an Olympic final.  The issues include the following:
  1. Few studies used trained individuals
  2. There are large individual variations in menstrual and premenstural symptoms between individuals.  Not only do some females suffer a lot more than others, but the timing of adverse symptoms may vary between individuals.  Scientific studies, by their very nature look at group average responses, but each athlete is an individual, and research based on average response is of little use in the performance environment.
  3. Determining the exact phase of the menstural cycle is difficult without measuring hormone levels.  There may be large variations in progesterone levels from one day to the next during the luteal phase of the cycle, so standardising testing points is notoriously difficult.
  4. In order to be scientifically sound, most studies take objective measures of muscle strength (or other variable), taking away the psychological element of performance.  In the real sporting world, psychological factors such as motivation will play a role.
  5. Because there is little scientific evidence to support menstrual cycle detriments to performance, there has been little research into what athletes who do suffer can do.

Menstrual pain and performance

The indirect effect of menstrual pain, and premenstrual symptoms such as fatigue, upste stomach, bloating, constipation, diarrhoea and headaches, are far more likely to be detrimental to performance that the direct effects of oestrogen or progesterone on muscle strength, carbohydrate metabolism or ventilation.

Dysmenorrhoea - very severe pain which precedes and/or accompanies menstruation and which interferes with daily activity - is experienced by some women.  While there is nothing to suggest that dysmenorrhoea is greater among athletes, it is obvious that this level of pain would affect performance.

The risk of anaemia

Anaemia is one of the greatest contributors to unexplained poor performance in female athletes. Those with regular heavy periods may be at particular risk or anaemia.  While all female athletes should have their haemoglobin and ferritin levels monitored, those with high monthly blood loss should be particularly cautious.

Menstrual Dysfunction

For all too many athletes, the problem is not menstrual pain, premenstrual symptoms, or cyclical variations in performance, but rather the complete absence of menstruation at all. Some studies have suggested that menstrual dysfunction may be as high as 50% in some endurance athletes (Wakat et al., 1982). While the absence of monthly pain and discomfort may not be top of an athlete's list of worries, inadequate levels of reproductive hormones can have much more far reaching consequences than any potential variation in performance over the cycle. Prolonged absence of menstruation (known as amenorrhoea) can have detrimental, irreversible and life-long effects on bone health, cardiovascular health, and even diabetes risk.  Infertility is also a potential problem, though in many cases this is reversible. While osteoporosis in later life may not be of immediate concern to a high performance athlete looking for Olympic glory, the associated increased stress fracture risk is, and time lost through injury will have a much greater effect on performance than any cyclical change in oestrogen or progesterone.  The consequences of amenorrhoea are compounded by its causes, with inadequate energy intake and low body fat percentages major contributors to the premature ageing of bone often seen in athletes.  The phenomenon, known as The Female Athlete Triad, has been covered in a separate post.

Regulating the cycle

In addition to using it as a form of birth control, athletes may use the contraceptive pill, which contains of low doses of oestrogen and progestins (substances which mimic the actions of progesterone), to control menstrual dysfunction, reduce menstrual discomfort and PMS symptoms, and to ensure that important competitions do not coincide with menses.  The pill can also be used to replace absent hormones in those with amenorrhoea.

Some studies have compared muscle strength, bone health, injury risk and various other physiological parameters between individuals using the pill and those with natural periods.  While the results are largely inconclusive, there doesn't appear to be any major differences in physiological parameters between the two groups.

It should be noted that oral contraceptives have changed considerably over the years, and not all research is relevant in the modern context.  Some research showing differences between oral contraceptive users and those not taking the pill may no longer be valid.

Regular natural cycles are preferable from a bone health perspective, but some level of hormones is better than none, and the pill, or other form of hormone replacement, may be prescribed for those with amenorrhoea.  The underlying causes of amenorrhoea should, however, also be addressed. Progesterone only pills or contraceptive injections may have sever detrimental effects on bone health. Depot medrozyprogesterone acetate (DMPA), an injectable, progesterone-only contraceptive, which may offer relief to those with sever menstrual symptoms, are associated with significantly reduced bone mineral density.

There are some things to be aware of if using the oral contraceptive pill.  Oral contraceptive use has been associated with significantly reduced serum levels of B Vitamins.

The aforementioned recent media coverage of the topic (Lewis, 2015) indicated that short-term interventions to delay menses is not the solution.  British 800m athlete Jessica Judd was given norethisterone, a hormonal tablet, to prevent her period - which was due on the day of the 800m heats at the 2013 World Championship - interfering with her performance, despite other female athletes knowing that this wasn't a solution.  Judd underperformed,

The final question

Should top athletes, often portrayed as invincible heroines, capable of overcoming even the most painful of hurdles and setbacks, be blaming something as common as a period for a sub-par performance?  Dam right they should.  And what's more, with the seemingly high rates of menstrual dysfunction in athletes, and the severe consequences of prolonged amenorrhoea, we should be celebrating the very fact that elite athletes are menstruating at all.

Recommendations

  • Athletes who experience very heavy periods should be particularly aware of the risk of anaemia. They should be aware of the signs and symptoms of low iron levels, have their ferritin and haemoglobin levels checked regularly, and act accordingly.
  • Though there is little scientific evidence to suggest that performance is affected by the menstrual cycle, considerable anecdotal evidence suggests that some athletes experience dips in performance in and around menses. Athletes with severe dysmenorrhoea may look to regulate their cycle so that menses doesn't coincide with an important event. This should be planned well in advance, and short-term measures should be avoided.
  • Progesterone-only contraceptives may increase bone turnover and/or reduce bone mineral density, placing an athlete at increased risk of stress fractures. Where possible, such contraceptives should be avoided.
  • The menstrual cycle, and other female issues, can be a major factor in an athlete's life. Coaches should be open to discussion of menstruation with their athletes, and aware of potential female health issues.

References and useful reading

  • Lewis, A. Curse or myth - do periods affect performance? BBC Sport Website, 22/1/15, retrieved 13/2/15
  • Paula Radcliffe: Sport has not learned about periods BBC Sport Website, 22/1/15, retrieved 14/2/15
  • Wakat, D, Sweeney, K, Rogol, A (1982) Reproductive system function in women cross-country runners. Medicine and Science in Sports and Exercise, 14, 263-269. Abstract
  • Zaharieva, E (1965) Survey of sports-women at the Tokyo Olympics. Journal of Sports Medicine and Physical Fitness, 5, 215.
  • Greeves, J, Cable, N, Rielly, T, Kingston, C (1999) Changes in muscle strength in women following the menopause: a longitudinal assessment of the efficacy of hormone replacement therapy. Clinical Science, 97, 79-84. Full text
  • Phillips, S, Gopinathan, J, Meehan, K, Bruce, S, Woledge, R  (1993a) Muscle strength changes during the menstual cycle in human adductor pollicis. Journal of physiology, 473: 125. 
  • Skelton, D, Phillips, S, Bruce C, Naylor, C, Woledge, R (1999) Hormone replacement therapy increases isometric muscle strength of adductor pollicis in postmenopausal women. Clinical Science, 96: 357-364. Full text.
  • Jacobson, B, Lentz, W, Kulling, F (1998) Strength and performance perceptions differences between four phases of the menstrual cycle. Medicine and Science in Sports and Exercise, 30: S208. 
  • Phillips, S, Rook, K, Siddle, N, Bruce, S, Woledge, R (1993b) Muscle weakness in women occurs at an earlier age than in men, but strength is preserved by hormone replacement therapy. Clinical Science, 84: 95-98. 
  • Phillips, S, Sanderson, A, Birch, K, Bruce S, Woledge, R (1996) Changes in maximal voluntary force of human adductor pollicis muscle during the menstural cycle.  Journal of Physiology, 496: 551-557.
  • Tenaglia, S, McLellan, T, Klentrou, P (1999) Influences of menstrual cycle and oral contraceptive on tolerance to uncompensable heat stress.  European Journal of Applied Physiology, 80: 76-83.
  • Moller-Nielse, I, Hammer, M (1989) Women's soccer injuries in relation to the menstrual cycle phase and oral contraceptive use. Medicine and Science in Sports and exercise, 21: 126-129.
  • Hall Jurkowski, J, Jones, N, Toews, C, Sutton, J (1981) Effects of menstrual cycle on blood lactate, O2 delivery, and performance during exercise.  Journal of Applied Phyiology. 51: 1493-1499.
  • Frankovich, R, Lebrun, C (2000) Menstrual cycle, contraception, and performance. The Athletic Woman, 19, 251-271. Full text
  • Bennell, K, White, S, Crossley, K (1999) The oral contraceptive pill: a revolution for sportswomen? British Journal of Sports Medicine, 33, 231-238. Full text

No comments:

Post a comment