Have you noticed changes in your HRV (heart rate variability) throughout your cycle? Hormones influence just about everything; your nervous system is no exception.
HRV measures the time difference between heart beats. Your heart rate varies from beat to beat. A heart rate of 60 beats per minute is not one beat every second, it might be less than a second between beats or more than a second but averages out to be 60 beats in one minute. This fluctuation or change in time between beats is called heart rate variability or HRV.
HRV is under the influence of both the sympathetic (flight or fight) and parasympathetic (rest & digest) nervous systems. The sympathetic and parasympathetic nervous systems are part of your autonomic nervous system – the part of your brain that regulates all the involuntary or unconscious bodily functions like breathing, heart rate, blood pressure and alternate, like a seesaw as to which system is more dominant. Ideally there’s balance between the two, meaning you move through the day alternating between feeling more alert (sympathetic dominant) or more relaxed (parasympathetic dominant) at different times.
When the sympathetic nervous system is dominant your heart rate increases, breathing quickens, blood pressure rises, and less energy or resources go towards digestion and recovery. The opposite effect is at play when the parasympathetic system is dominant – breathing slows down, heart rate decreases, and more blood flows to your digestive tract.
Since both systems exert different effects on heart rate and HRV, we can use HRV and nighttime resting heart rate as markers of recovery. Sympathetic stimulation lowers your HRV, fewer variations between heartbeats whereas parasympathetic stimulation raises HRV showing more variance in timing of each heartbeat.
HRV and resting heartrate are the main markers used with sleep and fitness trackers that offer you insights or markers of recovery. They’re tracking your HRV and heartrate and the longer you wear them the more data they have to determine what’s “normal”. How your HRV and heartrate shift away from normal short-term and long-term drive the recommendations of needing more or less recovery.
Progesterone stimulates your sympathetic nervous system. This results in a slight lowering of your HRV in a high hormone phase. High hormone being the week before your period. This isn’t a false lowering; this is something to heed and adjust for. When you’re in a high hormone phase, when your estrogen and progesterone are at their highest (also called the luteal phase) you are less resilient to stress. Another way to say this is training and all forms of stress will be amplified in this high hormone phase because your hormones are pushing you further into a sympathetic or alert state. With less balance between the sympathetic and parasympathetic states, it’s somewhat harder to get adequate recovery.
In the high hormone phase your core temperature goes up, your body uses more amino acids, sleep can be disrupted and there’s more inflammation. Not to mention the catabolic (breaking down) effect of progesterone. These hormonally induced shifts all add to the catabolic and inflammatory effects of exercise.
You can still train hard and race fiercely in this period as you can in any phase of your cycle. You just need to know how to adjust your nutrition and recovery to best support what’s happening in your body.
One important adjustment you can make if your training and schedule allow is to align your deload week with your high hormone week. Everyone needs a deload week, adding it to your high hormone phase is doubly effective. Next to that important step you can increase your opportunities to sleep, bump up your protein intake and take extra care to ensure you’re eating enough.
You can also look at my Recovery Optimization Tool Kit. It’s free and the focus is on balancing the sympathetic and parasympathetic nervous systems. We’re usually sympathetic dominant with our busy schedules and endless demands, bringing in simple yet effective strategies to calm our nervous system goes a long way to not let hormonal fluctuations impede our training, careers, and pursuits.
I believe the most powerful component of understanding your body and your physiology is how you can adapt and adjust to keep crushing your goals! When you know what’s happening and what to expect you can prepare for it and keep moving forward.
As with everything, you need to track and listen to your body to find its rhythm and nuances. Getting specific with what your body needs is the best thing you can do to live your best and stay in pursuit of your biggest goals!