Well, I was blessed to have run a full marathon on 'those days' and didn't really mind; the real nightmare for me is the week before I start my period (if I have it, which is usually 'off-season', in the colder winter months, when my inner sloth cuts back the mileage - we'll come back to that.) I was often wandering why what comes so easy one week later seems like an impossible feat just a few days before... it didn't take long to find the answer. I am a woman, I have a menstrual cycle, and my performance / physical capacity in general is acutely affected by two sex hormones: oestrogen and progesterone.
Oestrogen rules the first half of your cycle and is your buddy. In the follicular phase, the increasing concentration of estrogen will:
- adjust your body temperature set-point down in your hypothalamus - that's why your body temperature drops during this phase and your body responds to the temperature outside quicker by switching on its cooling mechanism. As a result, you don't feel like your boiling as you may towards the end of the luteal phase;
- your body uses more fat as energy source - estrogen promotes and speeds up the use of fat as energy source, thus helping you spare your glycogen reserves, and increasing your endurance on long runs;
- your muscles build up strength more quickly - in one study, quadriceps femoris strength after a series of 12 repetitions every second day over the two phases was tested, and - surprise surprise - the strength gains were at 27.6 per cent during the follicular phase training vs only 10.5 per cent during the luteal phase
- your breathing activity goes down - and since we associate our breathing activity (how fast we get 'winded') with perceived effort, running in your mid-follicural phase will seem easier;
- you don't retain so much water - hence you are lighter and experience less swelling; your blood circulation is also more efficient then;
Progesterone is king during the luteal phase and this is the bad guy who gives you PMS, increases your apetite so that you consume roughly 12% more calories than during the follicular phase, sets your body temperature at a higher level, thus putting you at risk of overheating, ratchets up your ventilatory activity, thus making you feel more winded, and makes you use mainly carbs as your energy source, thus making it harder for you to burn fat and stay on track for a longer run.
Period holidays, anyone? Amenorrhea
I mean, honestly, who actually invented the menstrual cycle in the first place? If you were to choose, wouldn't you rather...get rid of it at all? So most of endurance athletes actually welcome secondary amenorrhea - the condition when you period magically disappears as you increase your mileage, and replace your adipose tissue with muscle (when your fat stores edge towards the dangerously low, erm, 15 %) - your body thinks you are starving and reacts by shutting off oestrogen production (it's clearly not the best time to have a baby!). This may sound good enough, but estrogen plays one more imprtant role in your body - it regulates calcium absorbtion in your bones. Hence, low oestrogen due to excessive training may increase your risk of stress fractures. Not exactly what you want!
One thing we don't really think about is how sex hormones and menstrual cycle affect our performance. And it does. Don't stop running in the run up or on your period, but be considerate to yourself - it doesn't mean you're a bad runner if you feel winded and demoralized on these days!
Sources:
http://ubermotherrunner.com/2013/04/10/womens-hormones-and-running-guest-post-by-jason-karp-ph-d/
http://www.runnersworld.co.uk/staying-healthy/30-things-every-woman-should-know-about-running/285.html
http://www.elitefts.com/education/training/women-running-into-trouble/
http://www.shutupandrun.net/2012/11/how-your-period-affects-running.html
http://www.active.com/running/Articles/8-Ways-Estrogen-and-Progesterone-Affect-Your-Running?page=2
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