How to calculate your hydration
Hydration is more of a marketing campaign than a scientific campaign – have you ever stopped to consider if you really need 8 to 10 glasses of water a day? This is the same myth and blunder as the recommendation of 10,000 steps a day. The magic number “10,000” dates back to a marketing campaign conducted shortly before the start of the 1964 Tokyo Olympic Games. A company began selling a pedometer called the Manpo-kei: “man” meaning 10,000, “po” meaning steps and “kei” meaning meter. It was hugely successful, and the number seems to have stuck.
What you are looking for is Elevated Plasma Volume. Elevated plasma volume occurs when sodium is retained in the body, water is as well. This retention results in increased plasma and subsequently increased blood volume. Water alone, is not enough to do this.
There are some recommendations on how to do this BUT but they are not taking into account that there are specifically some sex differences in hormone pertubations that affect hydration and what us women need. You might ask why you need elevated plasma volume and the simple answer is successful adaptation through your training programme.
What you might consider before deciding on your hydration strategy, is that there are sex differences in renal water and electrolyte retention. Many consider this subtle and probably not of consequence and this is really big misstep in a position stand. The science behind this has not really been reviewed and a critical eye taken to the science and studies that are out there specific to women.
The initial studies started way back in the 80s with Stephenson and Kolka, where they were looking at hydration parameters and thermal regulatory parameters in female soldiers so it is known that this information exists but it is not widely used nor implemented into the hydration products or recommendations that you buy into.
It has been known for a very long time that there are sex differences between sweat rates, sodium losses, blood sodium levels at the end of exercise and finally someone has quantified it in a particular study just this year 2019. From this study it is known that there are sex differences between total body sweat rates, like men sweat more than women, and that there are some women that do have greater sweat rates that can rival some men, but in general have a lower sweat rate.
Sweat rates are greater in the luteal phase, but it occurs at a later onset so when you are looking specifically at follicular versus luteal phase, there can be a little bit of a difference , but it’s that heat generation at the start that becomes the metric that most people are looking at.
We also know that there are sweat sodium loss differences . Women lose way less sodium than men do in sweat. In the high hormone phase, we have less sweat sodium because across the board, our body has been kicking out more total body sodium and not retaining more, due to a switchover in our plasma osmolality and our hormones responsible for retaining sodium aldosterone, because progesterone and aldosterone compete for the same receptor site. When progesterone is elevated, aldosterone cannot tell the body to conserve more sodium so your body kicks out more.
(Aldosterone, the main mineralocorticoid hormone, is a steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands and colon).
Our sweat sodium is lower in the luteal phase than it is in the follicular phase, so when you are looking across the phases, and we know specifically that women have lower sweat sodium concentrations than men. When we look at total body sweat losses, this isn’t quite as large of a difference but there are still losses and total body sweat sodium losses, and this is dependent on where they collected the sweat which is why in this study there was no great difference because they used sweat patches in the same locations of the body. We know that the type of sweating and the sweat onset are patterned differently across men’s bodies than women’s.
This is why methods like Precision Hydration are actually not precise because they take one test at a particular time of the month, time of day, state of hydration, climate etc.
So how do I know how much I need?
Do your usual hydration and use a urine dipstick that has a urine-specificity gravity (USG), and you want to see what happens with that USG change.
So do your usual hydration and a specific training session and that’s your baseline (Test A).
You want to measure your urine-specific gravity before and after training, and if it’s longer than 2 ½ hours and you have a pee in the middle of it, see what your USG is doing and see if your hydration drink is actually working for you.
Then a week later, do the same test but use a functional hydration drink (with no carb added and high electrolyte) so that you’re actually absorbing that fluid and then compare the USG outcome on both tests.
You can also have a competition with your teammates and see who can wake up the most hydrated!
The urine-specific dipstick is a really good way of determining how hydrated you are and what kind of things you need to do, as if you come out significantly dehydrated in test A and then you do all the recovery metrics and you believe you’re rehydrated, and then wake up the next morning and you’re still dehydrated then you going to get in a chronic state of dehydration or hypohydration, with slightly low body water that’s going to affect fatigue, recovery, cognition, and adaptations.
Then when you do test B, see what happens when you do a specific hydration intervention.
So that’s what you’re drinking, how often you’re drinking, and change it up and see.
What is your hydration metric at the end of test B, and then the next morning?
I would love to hear your results!https://www.ncbi.nlm.nih.gov/pubmed/31230518 J Sports Sci. 2019 Oct;37(20):2356-2366. doi: 10.1080/02640414.2019.1633159. Epub 2019 Jun 2 https://www.ncbi.nlm.nih.gov/pubmed/25230913 Tohoku J Exp Med. 2014 Oct;234(2):117-22.