Nix Hydration Biosensor
Introduction
I received the Nix Hydration Biosensor early this year - having never heard of the product. Promo materials at the time mentioned Zdeno Chara using the product successfully for his new hobby of marathon running. As a big hockey fan, this was eye-catching just from a marketability point of view. Chara is something like 7 ft tall (on skates?) - I believe the tallest hockey player ever to play in the NHL.
Hockey digression aside, I was also unaware that such (purported) technology even existed - that is, analyzing/measuring sweat rate during exercise. I’ve been on somewhat of a journey, especially over the past several years (as most ultrarunners also tend to be), trying to dial in my fueling and hydration strategies. My biggest breakthrough was discovering Precision Hydration products several years ago- their neutral flavoring and focus on the salt/sweat aspect of hydration has been a game changer for me.
You’ve probably seen their products all over - they’ve really grown a lot, even in the big-time cycling world. Top cyclists undergo laboratory sweat-testing to determine the range of products (i.e. electrolyte/sodium levels) that would work best for them. I”ve long wanted to go to a lab for one of these tests, but they don’t have any testing sites near me, and I haven’t been able to coordinate something in another city.
So in my head, I was wondering - could the Nix Biosensor be a substitute on some level for this type of sweat testing? IF I could get a somewhat accurate reading of sweat volume and composition on the run - wouldn’t that be pretty much the ideal test scenario? Lab testing is great and all, but of course lab conditions cannot necessarily replicate the myriad of conditions you face out in the real world. So yes, the idea is extremely intriguing.. The execution…
How it works
Mike P: The Nix Biosensor itself is made up of two components - the sensor itself, and a non-reusable adhesive patch which you stick to your upper arm. First you stick the patch on your arm, then line up the sensor on the patch, twist, click, and you’re all set. You may wonder about placement of the patch, and how that relates to sweat readings. Don’t you sweat more in other areas? Underarms? Other essential areas? Like many other aspects of the sensor and this analysis - I’m not qualified to dig too deep into the “sciency” aspects of everything. So keep in mind I’m just giving the user perspective here.
Nix, through their proprietary data analysis, has determined a generalized correlation between your “actual” sweat rate and the sweat rate from a somewhat convenient location to get readings on the run - the upper arm. Like many aspects of this technology, you kind of have to take their word for it, and go with it.
So I found the patch itself to be unobtrusive and pretty much un-noticeable on the run. Yes, I know it’s there, but it didn’t bother me in any way. I ran a couple of raceswith it, ranging from 2 to 9+ hours, with no issue. The adhesive did not loosen at all, and also peeled off afterwards without fuss.
There are two ways to use the Nix sensor for on-the-run analysis. The primary way is to connect the sensor via Bluetooth to your smartphone. The Nix app then analyzes your sweat on the run, and provides notifications as to how much you should re-hydrate. There are notifications to “drink X oz”, and you can swipe on your phone to indicate that - yes, I drank that amount. It tracks the total volume of sweat lost, as well as the amount of fluid consumed on the run. The idea is to keep somewhat of a balance.
I find this on-the-run use case to be a bit cumbersome. I don’t typically carry my phone anyway, for one thing, and usually I’m either paying attention to other things, especially if it’s a race scenario, or conversely - trying to pay less attention to things at times. But of course during the times where you would be using the biosensor - that should be considered a data-gathering session, so focus should be required in some sense.
Luckily, the second scenario is that you can wear the Nix sensor, collect the data, and analyze afterwards. Here you eschew the on-the-run notifications and simply wear the patch on the run.
For this, you still need to pair the sensor with the Nix app on your phone, then start an activity within the app, then stop the activity on the phone when you are done. Note- the phone does not need to be with you (you can even leave it at home or in the car - with the app’s workout timer running).
The data is collected on the sensor on your arm, then transferred to the Nix app later on. Keep in mind - the Nix data is completely separate from your recorded activity data on your watch. There is no native data integration, so you should consider the Nix data as a completely separate dataset. The recorded data then shows up the same way within the Nix smartphone app as it would have if you had carried your phone the entire time.
If you are wondering about integration on your watch
Nix also has both a Garmin Device app and data field which you can download via the Connect IQ store. In this way, you can receive the hydration notifications directly on your watch. BUT - the Nix sensor itself never directly connects to your watch. I.e. tt is not a paired accessory on your watch. For the watch integration to work, you need to carry your smartphone on the run - the on-the-run data then flows from the sensor to your phone to your watch.
Yes, this is quite a convoluted setup. But in the absence of direct watch pairing or native datafield integration, it’s the best they can come up with. This method is really a non-starter for me. Perhaps it would be convenient to receive the hydration notifications on your watch - but you still need to carry your phone for it to work. It just seems like another extra step in the process making it more complicated.
The Good
A Test Race
Mike P: My first “test” was an early season extreme trail race - 4+ hours, 19 miles, 7,000 ft+ of vert. I went full out during the race - perhaps too much so for that early in the season, and actually dehydrated myself quite a bit (based on feel). I wore the sensor during the race, but started the activity on my phone, and left it in my bag at the start. After the race, I stopped the activity on my phone.
[A snippet from the spreadsheet downloaded via the app - notice the time is 3+ hours. The race was actually a little over 2 hours, but I wasn’t able to get to my car right away to stop the activity]
Note - the data needs to be manually analyzed in this scenario. The app will show averages based on the total activity time - which includes extra time before and after the race since I didn’t carry my phone with me. The Nix app allows you to manually export a spreadsheet with the hydration data. Here you’ll have to manually analyze the data, and/or re-average everything out as you see fit.
[Another snippet where I manually edited the spreadsheet - cutting out the non-activity time. I also re-adjusted the averages. This gives me accurate data for analysis. The activity cannot be cropped within the smartphone app - that would be immensely helpful.]
Data Analysis
In looking at the data - it showed, at least by my estimation, a very high amount of fluids that needed to be consumed. No way could I possibly drink that volume of fluids in this scenario.
Was this accurate? Possibly? I did get dehydrated during the race. But still that’s a lot. Interestingly, given the elevation change in portions of the race - long sustained climbs at high effort, long descent at low (sweat) effort, and even a few patches with very (relatively) humid conditions.
I did see variations in sweat rate over the different sections. Interesting. This leads me to believe that the sensor is reading relatively accurately.
The big question though is - relative to what? And also - what to make of the absolute values provided? That’s pretty much what I was getting at earlier - you kind of have to take them at their word if you’re looking at the actual values themselves.
[Data from a workout within the Nix app, Nix Index is based on weather conditions]
[The 27 oz “replenished” is what you enter during the run, or afterwards]
Nix also provides a further breakdown of sweat data beyond just pure Fluid Loss. They also give values for Total Electrolyte Loss, Sodium Loss, and Sweat Composition. The Electrolyte/Sodium Loss values are broken down into per hour values. This way you can get a sense of the amount of sodium you should look to take in, independent of the actual volume of fluid.
The Sweat Composition value (based on total electrolytes - not just sodium) can be used in conjunction with a provided Hydration Beverage Chart. This chart lists the electrolyte composition of many popular hydration products. The idea is that you should choose a product accordingly to match the level of electrolytes you are losing on the run.
Cost
Let’s just take it as a given that you trust the Nix data and analysis - or at least you have figured a way to correlate its data to some level of fluid intake/composition that works for you. The cost of the Biosensor itself is $129 which includes 4 non-reusable patches. That’s 4 individualized sweat tests, in conditions as specific as you can make them. (Refill patches are also sold - currently 4 for $25).
How much does a lab sweat test cost? Easily several hundred dollars. Then of course the data you get there is at least somewhat influenced by the conditions inside the lab. Obviously, on the run, in the field, data collection (BIG CAVEAT - if accurate) would be preferable. So assuming you are somewhat comfortable with the data analysis - after the initial $129 outlay, $6.25 for a personal sweat test is an amazing value.
Other Test Cases
Following that initial test run/race, I wore the Nix sensor for several longer training runs during the peak of the hot summer months. The sweat rates that I got seemed to track according to the weather and effort. I got values that were lower than that initial test race, which confirmed (?) that those very high values from the race were accurate (at least - relatively speaking). Could this be an indicator or at least confirmation that I really need to be taking in more fluids during runs - especially higher efforts like races?
[“Sweat Profile” is a composition of all of your workouts. Unfortunately, this does average in the time before and after workouts when I did not carry my phone with me. Also, I had one test run with extremely wonky data - saying I needed to drink 40+ oz per hour - in conditions that clearly were not the case. This skews my data - and I should probably delete that workout from my app]
I also found the Sweat Composition data to be useful. At a minimum, it seemed to at least provide a sanity check as far as things I had learned or experimented with before even using the Nix
sensor. Yes, I seem to be a “salty” sweater, and yes, it seems like I should be taking in more fluids than I have been in the past. I’ve been leaning into this direction through my usage of Precision Hydration products over the past few years. The Nix data does seem to track with my own personal testing, so as far as I’m concerned - it does seem “accurate” in a sense.
The Bad
Tech integration/bugs
This is the major issue with the Nix system. I’ve described above the test cases, runs, and data analysis - when everything works. Unfortunately it doesn’t “just work” most of the time. Bluetooth connectivity between the pod and the smartphone app is spotty at best. Any type of connection or pairing that displays a progress indicator - is completely unreliable. A percentage of whatever is going on has no bearing on the actual completion time.
In fact, whenever I use the pod, I have to completely “forget” the pod via the app, and reconnect it as if it was the first time. Maybe once or twice it actually reconnected, but I believe only during the same session/day. If I use the sensor one day, then want to use it again a week later - I would need to completely disconnect/reconnect the pod. Very frustrating.
When I followed the process described above (capturing the data without actually carrying my smartphone) this process was also highly buggy. After stopping the workout, the process of syncing the data from the pod would take excessively long - I’m talking 10s of minutes, sometimes 30+, and sometimes it would never finish at all.
[Unfortunately - need to do this many times]
The app gives you a message when the sync fails where you can try to rescue your lost data via the Help section. This worked a couple of times for me, and a couple of times the data was completely lost - including a 50 mile race where I wore the sensor for 9 hours. Again highly frustrating, and not to mention - a waste of a sensor patch (and $$$).
Overall, it just seems like the tech integrations are not ready for primetime. I haven’t noticed any firmware updates since I received the pod, but perhaps I need to check again. It’s definitely a bummer to have the entire process be so unreliable the majority of the time.
[This doesn’t even work sometimes]
As I’m typing this now, I thought about checking to see if there are any updates. I’m actually trying to connect my pod to the app, which is not working. I also can’t “forget” it either - it just returns to the previous screen and the pod still shows up ??? Maybe I’ll just let it “rest” for a few days and try again later???
Accuracy
If you’ve read this far - you’ve noticed that my testing and review is littered with “assumptions of accuracy”, or essentially “buying in” to what Nix is selling here. I don’t really see any way around this. I’m sure there may be qualified scientists that have a bone to pick with some of the Nix data and claims - but I’m just not that person. I’m also not the person to dispute those arguments either.
If you’re in that boat (skeptical) there’s really nothing I can claim to prove the Nix data is “accurate” or useful. I can only report that it does seem to track with my personal testing outside of the Nix device, so I’d ultimately lean towards accepting their data and claims.
Cost
Similar to accuracy - I’ve listed cost as both “good” and “bad”. If you believe in the data - at least in the sense of its “relative” accuracy - then the cost falls into the “pro” category. If you’re a complete skeptic and see the entire setup along the lines of snake oil - the cost factor will fall into the “con” category.
Conclusion
Mike P: The idea behind the Nix biosensor is very promising - right up my alley in fact as an ultrarunning data geek. Being able to test your sweat rate and perhaps more importantly sweat composition in different weather scenarios (cold, warm, dry, humid, hot, etc.) as well as effort scenarios has the potential to be a game changer. That is of course assuming that the data is reasonable, accurate, and trustworthy. I’ve refrained from delving into scientific considerations throughout this review. As much as that is important, I just don’t see it being feasible.
What I have found is that the data and information provided by the Nix sensors does seem to be relatively consistent across testing sessions. I’ve come into this testing with an improving sense of my own personal fueling and hydration needs. Perhaps that gives a certain bias, but the fact that the data somewhat matches my own testing and feelings about hydration - I take it as a good thing.
If the Nix would have told me that I need to be drinking less when all signs point to me needing to actually drink more - then I’d be more concerned about the accuracy of the device. But my personal Nix data indicates that I should really be upping my fluid intakes - even a bit more than I have been over the past season or so. I have been dealing with cramping and dehydration issues in several races over the past several seasons. Given that history/context - I do find the Nix data to be accurate and actionable.
Unfortunately, the technical aspects of the setup and usage are a HUGE downside. If everything between the pod and the app - connections, syncing after workouts, etc., worked seamlessly - it would leave me with a much more positive experience using the product. As it stands now, I like the data, I do think it’s helpful, but it comes with a ton of frustration to actually use the product.
Constantly having to disconnect, reconnect, forget, re-pair the pod - is extremely frustrating to say the least. Also the vagary of syncing the pod post-run, the excessive duration of that process, having to recover data multiple times, even losing activity data completely (happened more than once) - unfortunately this has been a recurring part of the Nix experience.
Will I continue to use the product? As of now, I can’t connect the pod at all to the app, so step one will have to be possibly reinstalling the app itself on my phone and trying to set everything up again. Aside from that - I’ll probably take the findings that I have already and shoot for better execution of my hydration process. As with anything, knowledge is one thing, execution is another… But as for ordering more patches for continued use, I’ll say maybe..
The Nix Hydration Biosensor is available at Nix HERE
Mike Postaski currently focuses on long mountainous ultras - anywhere from 50K up to his favorite - 100M. 5'10", 138 lbs, midfoot/forefoot striker - he typically averages 70 mpw (mostly on trails), ramping up to 100+ mpw during race buildups. A recent 2:39 road marathoner, his easy running pace ranges from 7:30 - 9:00/mi. From 2022-23 Mike has won the Standhope 100M, IMTUF 100M, and Scout Mountain 100M trail ultras, winning the Scout 50M in 2024. He also set a CR of 123.74M at the Pulse Endurance Runs 24H and completed the Boise Trails Challenge on foot in 3 days 13 hours, besting the previous record by 7 hours. Mike's shoe preferences lean towards firmer, dense cushioning, and shoes with narrower profiles. He prefers extra forefoot space, especially for long ultras, and he strongly dislikes pointy toe boxes.
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