Fitness
Measuring bioactive nitric oxide during exercise could help improve fitness, and this new device provides real-time data
The heart is the master dispatcher for our lifeblood. It has the crucial burden of balancing physiological economics during rest, during a ride, and while recovering. If the heart can’t pump enough blood to equal demand for nutrients and oxygen, fatigue sets in, you bonk, and sometimes, you have to quit. Rest and replenishment are the only salvation.
It is well understood that the body’s managerial mechanisms run much deeper, especially during exercise. Governing a cyclist’s overall ability to continue putting out power during any type of effort are the cellular and molecular constituents produced and delivered alongside every contraction of the restless courier in our chest. Oxygen, glucose, fatty acids, lactate, hemoglobin, bicarbonate, nitric oxide — all are important, each playing a role in how well we are able to respond to the stresses of exercise. They also dictate how well the body can adapt and repair between exercise sessions.
We make an intentional point to try and measure and understand the importance of biomarkers and vitals in athletic training and performance, with the current boom in wearable technologies making it possible to deliver insights never previously fathomed. Though no lack of data exists, is there a best measure to understanding an athlete’s exercise capacity and fitness?
Being able to measure blood flow has been a decades-long quest in sports medicine. Exercise physiologists often focus on the mitochondria, bioenergetics, and oxygen consumption (VO2) as a pathway to understanding someone’s performance capacity and upper limits. Coaches use biological outputs such as lactate and heart rate layered atop metrics like power to guide training strategy. The integration of all of these somatic informatics is rightfully based on what we know as best practice today.
But what are the true regulators and rate limiters of performance? We know that the ability to do work (ride a bike) is based on a few basic orderly factors:
- Muscles need oxygen
- and fuel (glucose, fatty acids)
- to synthesize ATP
- which is used to output mechanical energy
- so that they can contract
- and work (exercise) can be done.
But a crucial step is missing: the regulation of delivering oxygen and fuel. The body was divinely designed to compensate and adapt to changing conditions, and at the level of muscle oxygenation and work output, here is how that concept is applied. At the onset of exercise, a shift in blood flow must occur to ensure oxygen and nutrients are delivered where they are needed most — your working skeletal muscles, the heart, and brain, primarily. The ability to measure and understand how this happens is crucial. As it turns out, one molecule is inadvertently responsible, and without it, everything else is impossible.
Hello, SNO.
Performance regulation: There’s a new kid in town.
Nitric oxide (NO) has been hailed as one of the most important regulators of cardiovascular health, impacting blood pressure, inflammation, and overall vascular function. It is a potent vasodilator, responsible for directing and improving blood flow to areas of the body where blood flow is needed most. This happens during periods of oxygen demand and supply mismatch, like exercise, and it happens almost immediately. The supplement market is booming with products that help athletes improve NO production, such as L-arginine, to help maximize blood flow to muscles during a workout.
All of this stated, the classic understanding of how NO is produced and directs blood flow is beginning to change, which inevitably impacts how we think of performance regulation. Let’s break it down. We know that:
- Muscles need oxygen,
- and oxygen is carried by hemoglobin in red blood cells.
- Oxygen must be transferred from red blood cells to muscles
- so work (exercise) can be done.
Further:
- When exercise starts,
- muscles begin consuming oxygen at a higher rate.
- A dip in available oxygen happens.
- Oxygen is increasingly offloaded from red blood cells to try and match the new demand.
Remember: supply must match demand.
Now what? An economic dance ensues between red blood cells (where oxygen is carried), and the oxygen tension in the muscle itself. A newer discovery has explained how this interplay impacts overall dispersion of blood during a workout so muscles can be adequately fueled and exercise can continue, and it is meticulously regulated.
During conditions where oxygen tension in muscles (and therefore red blood cells) decreases, a nitric oxide derivative called S-nitrosohemoglobin (SNO-Hb) is also produced and offloaded by hemoglobin alongside oxygen. SNO-Hb, part of a group of compounds called S-nitrosothiols, or SNOs, dilates the tiny blood vessels in the muscle tissue itself (capillaries, arterioles). Blood flow increases, and oxygen delivery can now meet the heightened demand. This goes for nutrient delivery too, like increased need for fatty acids and glucose.
Why is measuring SNO helpful?
It could be hypothesized that many of the foundational benefits of exercise are due to these well-controlled increases in blood flow. There is a system-wide effect on the heart and brain, too. Further, there are adaptations to the cardiovascular system and blood profile in response to training. More exercise leads to more hemoglobin, a larger blood volume, and a greater and faster NO response. The latter specifically leads to a better blood flow response, and therefore improved oxygen and nutrient delivery. Theoretically, the same goes for bioactive NO derivative, SNO, at the tissue level. In this perspective, SNO is sitting in the driver’s seat and orchestrating it all.
Devices exist on the market today that measure oxygen saturation in muscles and other tissues (SmO2 or tissue oximeters), but that only paints a partial picture of the impact certain types and intensities of exercise have on an individual. Being able to measure someone’s SNO response to exercise would offer the first look into the gatekeeper of muscle oxygenation. Why do we care? All of this impacts the ability for mitochondria to output adenosine triphosphate (ATP). It is also an indicator of muscular damage during injury and nourishment during rehabilitation. These processes all require oxygen.
Measuring SNO is specific, and it may indicate the readiness and effectiveness of exercise on a personalized level. It can be associative to overall VO2, and oxygen consumption specific to the muscle (called mVO2) as well. It may be an indicator of power output and capacity, and could also correlate to lactate efflux. Further, and most importantly, it can stand alone as its own measurement. As with anything truly new and disruptive, a lot of research needs to be conducted, but there is evidence indicating the usefulness of SNO as a novel biomarker to gauge fitness and performance.
How can we measure SNO? NNOXX has a device
There is a device available today that non-invasively measures SNO, plus muscle oxygenation (SmO2) and muscle oxygen consumption (mVO2) from a company called NNOXX. (Full disclosure: I have consulted with NNOXX on clinical and regulatory affairs.) It’s the only device of its kind, delivering continuously streaming data that can be accessed at any point during a ride or workout. NNOXX helps athletes understand the efficiency and effectiveness of an exercise by measuring these performance indicators directly in exercising muscle, in real time.
One differentiating thing about these biomarkers is that they are exercise “blind,” meaning you can ride or you can lift, and you will still produce SNO and use oxygen, just not in the same way (a topic for a different article). The $299 NNOXX device can be used to make individualized assessments during many types of exercise — biking, lifting, and running, as examples — and only needs to be placed on the exercising muscle during your workout.
So how can riders use NNOXX to help improve their cycling performance?

NNOXX provides a Performance Readiness Score
Muscle recovery can be impacted by insufficient calories, poor sleep, dehydration, overreaching, or even the onset of illness. NNOXX is differentiated because the biological assessments are measured and delivered in real-time based on rates of oxygenation and deoxygenation, plus the bioactive nitric oxide response while you’re exercising. All you have to do is a guided four-minute cycling protocol and the app will give you both a Muscle Readiness and Aerobic Readiness percentage tailored to your physiological status. You’ll be given a recommendation of how to proceed based on your score. You can also see a seven-day trend.
NNOXX can help you understand how well you performed compared to other rides or exercise sessions.
The app provides individualized performance indicators, including a Power Index, Endurance Index, and Economy. These indicators are based on your personal rates of muscle deoxygenation, reoxygenation and other factors, measured in real-time during your workout. After your workout is finished, you’ll receive your score for the day, your average range, and 60-day comparative trend.
This feature is really useful if riders have regular routes or workouts, and they’re interested in seeing if they’re improving, especially when making changes to their routine (e.g. more sleep, additional interval sessions, changes in recovery or dietary habits, or longer rides).
Further, users can potentially infer if a specific type of riding is best for them. For example, if the data shows you’re more efficient at climbing than previously thought, it may be something worth capitalizing on or integrating more often into your routine. The opposite can be a takeaway, too. If the app indicates you perform better doing power activities than long rides, you can use this to create a goal around improving your endurance.
What if I am new to mountain biking or cross-training and to improve my performance without hiring a coach or personal trainer?
The NNOXX app provides an AI-guided coach to customize your ride or other workout to be the most effective and efficient. The output is based on the effects of your real-time SNO production. As data is aggregated, workouts can be compared and personalized to your individual physical performance to help maximize gains.
For a new-to-market device and a new biomarker, the metrics provided by the device do seem to be physiologically reliable and accurate. Because the data is provided continuously with relatively no lag, the information can easily be compared to other performance indicators. Users can see how their body is compensating for increases in cadence or terrain grade, as examples.
NNOXX recently released a feature that allows users to import their Strava and Peloton data into the High Performance Platform on their website. Comparisons between SNO and SmO2 can be made alongside work, power, heart rate, and others on a single platform.
Again, the SNO biomarker and associated performance indicators are new. Like most things in science and medicine, it takes time to build up a bank of clinical evidence that is trustworthy, and the data on SNO as a performance biometric promises to evolve as discoveries are made and information is added. The digital technology boom is allowing researchers and developers to change the landscape at an unmatched speed, and NNOXX is a great example of what I believe is a positive outcome of the race.
Sources
Premont, R. T., Reynolds, J. D., Zhang, R., & Stamler, J. S. (2020). Role of nitric oxide carried by hemoglobin in cardiovascular physiology: developments on a three-gas respiratory cycle. Circulation research, 126(1), 129-158.
Reynolds, J. D., Posina, K., Zhu, L., Jenkins, T., Matto, F., Hausladen, A., … & Stamler, J. S. (2023). Control of tissue oxygenation by S-nitrosohemoglobin in human subjects. Proceedings of the National Academy of Sciences, 120(9), e2220769120.
Fitness
The Case for Ditching Your Fitness Trackers
Credit: René Ramos/Lifehacker/ZaZa studio/Adobe Stock/Andriy Onufriyenko/Moment/Vadym Kalitnyk/iStock/Getty Images
I have a love-hate relationship with the smartwatch on my wrist. This relationship is no doubt shaped by the fact that I write about fitness tech for a living, but I know I’m not alone in succumbing to an obsession with numbers from my wearables. Did I hit 10,000 steps? What’s my resting heart rate today? Is my sleep score better than yesterday’s? When did progressive overload turn into screen time overload, too?
The fitness tech boom is showing no signs of slowing down any time soon—and with it, we consume a constant stream of promises that this data will make us healthier, stronger, and faster. With the sheer amount of health insights potentially available to us at any time, it’s easy to get overwhelmed. I’ve watched my least health-anxious friends become consumed by metrics they’d never heard of two years ago. They’re tracking bone density trends, obsessing over cortisol levels, panicking about stress scores that fluctuate for reasons no algorithm can fully explain. I can feel my fitness trackers pull me away from genuine wellness and into a mental health disaster. The good news: When I look up from my screens and start talking to real people, I see I’m not alone in wanting to unplug and push back against the overly quantified self.
A growing anti-tech fitness movement
When I put out a call on Instagram asking people about their relationship with posting workout data and fitness content, I received hundreds of responses from people exhausted by the performance of fitness. Even if your only audience is your own reflection, simply owning a wearable can create a real barrier between feeling good about your body and your fitness journey. Did I work out enough today? Will my friends see that I skipped a workout? Should I push through injury to maintain my streak?
For these reasons, celebrity trainer Lauren Kleban says she doesn’t like to rely on wearables at all. “Counting steps or calories can quickly spiral into a bit of an obsession,” says Kleban, and that “takes the joy out of movement and away from learning what’s truly best for us.” She says her clients want to focus on their mind and body connection, now more than ever. There’s a real, growing desire to rebuild a sense of intuition that doesn’t depend on feedback from a watch.
Similarly, Marshall Weber, a certified personal trainer and owner of Jack City Fitness, says that he’s “definitely been surprised by the growing push towards unplugged fitness,” but that he “totally gets it.” Weber says he’s had clients express feeling “overwhelmed with their Fitbit or Apple Watch micromanaging their training.” When every workout becomes about numbers and keeping up with an average, it’s all too easy to lose touch with your body. “The anti-tech movement is about taking back that personal connection,” Weber says. After all, when was the last time you finished a workout and didn’t immediately look at your stats, but instead just noticed how you felt?
This is the paradox at the heart of fitness technology. Tools designed to help us understand our bodies have created a new kind of illiteracy. Maybe you can tell me why you’re aiming for Zone 2 workouts, but can’t actually recognize what that effort feels like without a screen telling you. In a sense, you might be outsourcing your own intuition to algorithms.
If nothing else, the data risks are real. (Because if you think you own all your health data, think again.) Every heart rate spike, every missed workout, every late-night stress indicator gets recorded, stored, and potentially shared. Still, for me, the more insidious risk is psychological: the erosion of our ability to know ourselves without consulting a device first.
What do you think so far?
How to unplug and exercise intuitively
So what does unplugged fitness actually look like in practice? It’s not about rejecting all technology or pretending GPS watches and heart rate monitors don’t have value—I promise. Look, I crave data and answers as much as—and maybe more than—the average gym-goer. I’m simply not woo-woo enough to ditch my Garmin altogether.
Instead, I argue for re-establishing a hierarchy in which technology serves your training, not the other way around. “Sometimes, the best performance boost is just learning to listen to what your body is saying and feeling,” says Weber. But what does “listening to your body” actually look like?
If you’re like me, and need to rebuild a connection with your body from the ground-up, try these approaches:
-
Start with tech-free workouts. Designate certain runs, yoga sessions, or strength workouts as completely unplugged. No watch, no phone, no tracking. Notice what changes when there’s no device to check.
-
Relearn your body’s signals. Can you gauge your effort level without looking at a heart rate monitor? Do you actually know what “recovery pace” feels like for you, or are you just matching a number? Practice assessing fatigue, energy, soreness, and readiness without checking your watch.
-
Replace metrics with sensory awareness. Instead of tracking pace, notice your breathing pattern. Instead of counting calories burned, pay attention to how your muscles feel. Instead of obsessing over sleep scores, ask yourself a simple question in the morning: how do I actually feel?
-
Set goals that can’t be gamified. Rather than chasing step counts or streak days, aim for qualitative improvements. Can you hold a plank with better form? Does that hill feel easier than last month? Are you enjoying your workouts more? These are the markers of real progress.
-
Create tech boundaries. Maybe you use your GPS watch for long runs but leave it home for everything else. Perhaps you track workouts but delete the social features. Find the minimum effective dose of technology that serves your goals without dominating your headspace.
-
Reconnect with in-person community. The loss of shared gym culture—people actually talking to each other instead of staying plugged into individual screens—represents more than just nostalgia. There’s real value in working out alongside others, in having conversations about training instead of just comparing data, in building knowledge through shared experience rather than algorithm-driven insights.
The bottom line
Unplugging is easier said than done, but you don’t need to go cold turkey. Maybe in the new year, you can set “body literacy” as a worthwhile resolution. At the end of the day, exercise should add to your life, not become another source of performance anxiety. It should be energizing, not exhausting—and I don’t just mean physically. The never-ending irony of modern fitness culture is that in our pursuit of optimal health, we keep inventing new forms of stress and anxiety. When all forms of wellness come with trackable metrics and social pressure, I think we’ve fundamentally missed the point.
Fitness
How to avoid exercise burnout and still build muscle, according to an expert
Many of us have experienced the overwhelming feeling of mental and physical exhaustion that comes with exercise burnout. When you push yourself too hard without sufficient rest and recovery, it ultimately becomes counterproductive to your fitness goals, and your energy will tank along with your motivation. Not only that, your performance will suffer when you overtrain and under-recover, and you’re left sinking further into the couch, wondering how you’ll lift that next weight, swim that next lap, or run that next mile.
With a combo of the right nutrition, rest, recovery, and lowering your training intensity, you can get back on track. To learn more about avoiding burnout and torching fat while sculpting muscle for men, I asked certified personal trainer and Vice President of Education for Body Fit Training, Steve Stonehouse, to share some of his vast knowledge on the subject. With decades of experience in fitness education, fitness programming, and personal training, Steve Stonehouse developed an in-depth knowledge of weight loss, improving body fat composition, building muscle, and the best exercise plans that generate serious results.
Expert advice on burning fat
The Manual: As the Vice President of Education for Body Fit Training, what are your top tips for burning fat and improving body composition for men?
Steve Stonehouse: As the programmer and head of education, this is a little cliché, but I go for balance. Not every workout can be this CrossFit type, give it all you’ve got, smoke yourself, and work out — that’s not sustainable. The other end of the spectrum is just walking at a moderate pace for 20 minutes on a treadmill three times a week, because that’s not going to do it either. There’s value in both of those scenarios.
It’s best to have a session or two each week where the intensity is very high, and you’re testing yourself and pushing yourself closer to your limits. That’s anaerobic exercise, which is 90% intensity or above. It’s fine, safe, and healthy to get there occasionally, but every workout can’t be one of those. Your body isn’t built to train that way; you’re gonna burn out, and you could get injured, or both.
There’s a place for some moderate intensity as well, so if I were focusing on heart rate, I would say in the 80s, so it’s hard but not max effort, and it’s more sustainable. When you’re in that 70 to high 80s range, we categorize that as building aerobic capacity. Overall, I suggest an approach with recovery, moderate intensity, and then high intensity every now and again to test yourself.
The best cardio for fat loss
TM: How does cardio help with fat loss, and what types of cardio do you recommend?
Steve Stonehouse: I’m a big fan of high-intensity cardio. Sometimes, people think if some is good, more is probably better, but more isn’t always better. If I were putting a program together for six days a week, I’d have three days as some type of cardio-driven day, and three of those days I would have some version of resistance training. Maybe some days are heavier, and other days are a little lighter with higher rep targets and less rest.
Of those three cardio days, I’d recommend that one of them be a high-intensity max effort type HIIT session. Another could be hard with a heart rate in the 80s, but not max effort. That third cardio day could be more metabolic conditioning, like kettlebell swings, sled pushes, rower, or SkiErg, and things like that.
Ramping up muscle growth
TM: What types of exercise are the most effective for ramping up muscle growth?
Steve Stonehouse: We’re moving into a great space right now in fitness, and it seems like every 10 or 15 years, there’s this new movement. CrossFit first popped up and led the charge for metabolic conditioning and no days off. It’s the idea that if you still feel good at the end of a workout, you didn’t train hard enough. I think we’re phasing out of that and into wanting to lift heavy again. People who wouldn’t have touched a barbell ten years ago are lifting heavy now.
Keep in mind that heavy is a relative term. You can get stronger with some lighter dumbbells, but there are limits to that. A blend is nice, but you do need to include those times when you’re lifting heavy and challenging yourself at a low rep target.
Say, I’m going to do barbell deadlifts for five reps. If I can do eight, then that weight is too light. It’s intended to be a weight that you can’t get 15 reps of. There are advantages to lifting heavy with low-rep targets and longer rest times. For example, we’re going to do four sets of five reps of barbell deadlifts with two minutes of rest in between sets. If you can do more than five or six reps, that weight is too light. There’s a lot of value in lifting heavy.
TM: We know it’s probably difficult to choose, but what are your top three favorite fat-burning, muscle-building exercises right now?
Steve Stonehouse:
- Barbell Zercher squat
- Barbell deadlift
- Flat barbell bench press
TM: How often should you work out to build muscle?
Steve Stonehouse: For the heavy session with five or six reps and longer rest periods, you could have a day each week that’s primarily focused on upper-body heavy strength training. Then, you could split it up and have another day that’s primarily focused on the lower body. You could do that, so you’re not in the gym for two hours; it’s more like a reasonable 45 or 50 minutes. If you were feeling ambitious, you could get a third one in toward the end of the week and have a bit of a mixed session where there’s not as much volume, but you have upper-body and lower-body focus.
With that type of heavy volume, you’re going to need a decent amount of time to rest. So, if I were doing a heavy bench press today, I probably wouldn’t do that again until next week — same thing with squats, deadlifts, or any larger main lifts.
Incorporating sufficient rest days and progressive overload
TM: Are rest days important for the best results?
Steve Stonehouse: Yes. Rest and recovery are two different things. A recovery session would include a bit of activity, but at a lower intensity. Recovery is restoring to a natural, healthy state, and rest is inactivity.
TM: With resistance training, do you recommend incorporating progressive overload, where you gradually increase the weights over time to develop muscle strength and mass?Steve Stonehouse: 100%. We do strength training regularly at BFT. We have a portion of our performance app, and you can enter your five-rep max. On different days, the performance app tells you how much weight you should be lifting on that day to appropriately follow that progressive overload model.
Fitness
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