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Shoe Clinic are proud to have...
Marnie Oberer as an Expert columnist.
Marnie is a nutritionist and athlete and has been the host of Eating Well on TV One for the past two years. She is a trained dietitian and has a degree and two postgraduate diplomas from the University of Otago.
By 28 Marnie had set up her own business consultancy, advising high performance athletes and teams. Marnie started competitive aerobics and caught the ‘marathon bug’ running in Australia, UK and USA.
Column 37, February 2011
Oral contraceptives and physical performance
In my first few years of running, after a baffling long plateau in my performance, my coach suggested the oral contraceptive (OCP) could be limiting my progression. I had also heard talk amongst fellow female runners about their negative experiences with the pill.
Soon after, I stopped taking my OCP (which contained both estrogen and progesterone) for several months. Within 2 weeks my performance improved measurably eg 20 secs faster over a 1500m race. Months later I restarted the pill, as a test, with negative effect.
My experiment could hardly be considered ‘scientific’, but it was evidence enough to me that the pill I was taking was limiting my performance.
What does the scientific literature say?
Currently the scientific literature, as well as the personal experiences of female runners taking the OCP, is varied.
One of the problems in trying to research the effects of the OCP on performance is that there are many different types eg they can contain progesterone only (otherwise known as the ‘mini-pill’), or a mixture of the sex hormones progesterone and estrogen (the ‘combination pill’). There are also around eight different types of progesterone that may be used, and varying ratios of progesterone to estrogen.
Other factors conflicting results include menstrual history, duration of OCP use, and the age at which women started on the OCP.
OCP and aerobic capacity
A Canadian trial published in 2003, involving 14 female athletes, demonstrated a mean reduction in aerobic capacity (VO2max) of 4.7% following 2 months of OCP usage.
Another similar study reported a 5% reduction in VO2max in a group of elite females after 2 months on the OCP. Maximum heart rate and endurance at 90% VO2max was not affected by the OCP in either study, and both sets of researchers concluded that the reductions in VO2max were reversible within 4-6 weeks of coming off the OCP.
Other studies have shown no impact of the OCP on performance however.
Even if the OCP does lead to a slight drop in VO2max, it is unclear whether this would translate to a reduction in performance, as the known benefits – for example, a reduction in pre-menstrual symptoms – might outweigh a slight drop in VO2max during training or competition.
OCP and body weight / body composition
The issue of weight gain is seen as a particular concern by athletes and coaches in distance running.
In a 2004 study of 26 endurance athletes, an increase in weight and body fat with the OCP was seen only in athletes who had erratic periods, or were not menstruating prior to the study. Importantly, however, there was little impact seen on performance. A very positive outcome in this study was the increase seen in bone mineral density.
While individuals respond differently to the OCP, most studies actually show no overall effect on body weight, especially with the newer, lower dose pills.
A 2009 study in Texas found that women on the OCP developed 40% less muscle mass when put on an intense workout regime comprising of 3 sessions a week, for 10 weeks. They seemed to have lower levels of muscle-building anabolic hormones, and higher levels of cortisol – a stress hormone associated with muscle break-down - than those not on the pill.
It was suggested that progestin - a synthetic form of progesterone – blocks the hormones that stimulate muscle growth. The researcher suggested those concerned with decreased muscle mass choose a lower dose OCP.
The big picture
A check-list of the possible pros and cons of the OCP for female athletes is set out below:
Advantages - Highly effective method of contraception, convenient and reversible
- Provides a source of estrogen for athletes not menstruating, decreasing their risk of stress-fractures/osteoporosis
- Reduces painful menstrual cramps
- May decrease pre-menstual symptoms (eg mood swings, nausea, headaches) which could negatively impact training/competition
- Can be used to manipulate the menstrual cycle for important events
- Associated with a decreased risk of ovarian and uterine cancer
- No known long-tem effect on fertility
- Possible protection from knee injuries by reducing the laxity in knee joints around ovulation
Disadvantages- Possibility of breakthrough bleeding, fluid retention, weight gain, breast tenderness and headaches (though these may be controlled by changing pills)
- No protection from sexually transmitted diseases
- Associated with a small increase in the risk of breast cancer if used for more than 10 years without having children
- Possibility of decreased VO2max, reducing performance??
- Possibility of reduced muscle mass
In summary, the evidence so far would suggest that women show differing individual responses to OCP use, both negative and positive. While the discrepancies are being examined, I would suggest female runners taking the OCP, monitor their own experiences – including when they are occurring in their cycle - and see a sports doctor to discuss the most suitable method of birth control while training or racing.
Marnie Oberer
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