The gear closet you do not need
You are looking at your gear closet on a Sunday afternoon. There is a watch with full mapping and a barometric altimeter. There is a chest strap you bought when you read that wrist-based heart rate was unreliable. There is a ring you wear at night for sleep tracking. There is a continuous glucose monitor you wore for two weeks last spring and never reordered. There is your phone, running three apps that each claim to read your readiness for tomorrow. There’s also a respiratory rate sensor that a friend gave you that you never figured out how to use.
You have spent, probably, two thousand dollars on all of it. You are not training measurably better than you were five years ago. You are training with more numbers.
There is a smaller version of this stack that does most of the useful work and stays out of the way enough for the training to be the training. What follows is what that smaller stack looks like, how to judge whether the next device marketed to you belongs in it, and how to keep the data honest once you own the tech.
What is a tech stack supposed to do for a mountain athlete?
A tech stack has three jobs. It records what you produced in a session, it reads what that production cost your body, and it establishes a recovery baseline across weeks.
Recording production means that pace, distance, vertical gain, and time at intensity, are captured so that one session can be compared to another over months and years. The cost is measured by heart rate response, perceived exertion, and the relationship between the two, which is the part of the stack that tells you whether you are getting fitter or accumulating fatigue. The recovery baseline is your resting heart rate, heart rate variability, and sleep, read as trends across weeks rather than as daily verdicts.
Two devices do most of that work. A GPS watch with a barometric altimeter handles production and a real heart rate monitor handles the cost. The recovery baseline builds itself out of those same two devices over time. Everything else is situational, and their function and utility depend on your needs.
Before you buy anything, answer this: which of the three jobs does this device do, and does it do that job better than what you already own? An honest answer prevents most of the wasted spending we see in our coaching practice.
How do you tell whether a new training device is worth buying?
All training technology travels the same arc. It is introduced, hyped past its actual capability, and then falls into disillusionment as early adopters find its limits. A smaller and more patient group works out what it genuinely offers, and eventually it settles into infrastructure that the next generation takes for granted. The useful question about a new device is not whether the technology works, but where on that arc it sits, and what your training looks like if you wait two years before buying it.
Heart rate monitoring is the cleanest case study available. The first wireless monitor reached the consumer market in 1983, and by the middle of the 1990s most serious endurance athletes had one. The hype phase taught athletes that they needed to know their heart rate, which was true, but it did not teach them what to do with the number. The learning phase took the endurance community roughly a decade and produced the skills we now treat as foundational: how to test for the aerobic and anaerobic thresholds, how to read cardiac drift, how to interpret heart rate against perceived effort, and how to recognize when heart rate is responding to heat, dehydration, poor sleep, a menstrual cycle phase, or an illness you have not noticed yet. The device does not do that work, the athlete has to.
Knowing where a category sits tells you how much of that interpretive work you will have to do yourself. Continuous glucose monitoring is moving through the middle of the arc about forty years behind heart rate. Pulse oximetry went through it more quietly. Respiratory rate is at the early end now and emerging in a new way.
What tech does a mountain athlete actually need?
You’ll need two devices: a GPS watch with a barometric altimeter, and a real heart rate input, meaning either a chest strap or an arm-mounted optical band. Roughly $500 to $1,000 for both, and less if you buy last season’s watch. Almost everything else is optional, and most of what is optional is decoration.
Sleep tracking and heart rate variability come along with most modern watches and rings and are useful for daily trends. A pulse oximeter earns its place if you are going to altitude or running a structured hypoxic protocol. A continuous glucose monitor could be useful for some specific situations. Respiratory rate is worth watching and it will be interesting to see the progression of some of the new devices coming to market this year.
Choosing the best GPS watch for mountain endurance sports
The specific model matters less than the four features: a barometric altimeter, accurate vertical-gain recording, long battery life, and the ability to read heart rate from an external sensor. The Garmin Fenix and Enduro series, the Coros Vertix 2S, and the Suunto Vertical all meet that standard.
The barometric altimeter is the load-bearing feature. Vertical gain is one of the two fundamental load metrics in mountain training, and GPS altitude is too noisy to carry it, with typical vertical errors of ten to fifty meters from satellite geometry and signal obstruction. A barometric altimeter measures air pressure directly and can detect a climb of a few steps, though it drifts as weather moves through. Modern watches combine the two, calibrating the barometer against GPS across a session, which gives vertical-gain recording accurate enough to compare one big day to another and one season to the last.
Battery life matters because mountain days are long. A watch that holds GPS for forty-five to sixty hours covers most expedition use. Pick the battery profile that matches the longest day you actually train for.
Keep in mind that the model released two seasons ago usually does about ninety percent of what the current one does, at a meaningfully lower price on the secondary market. Plenty of athletes upgrade the moment a new watch launches, and their old one is often the right purchase for someone who is training rather than collecting gear.
Why heart rate carries more weight in the mountains
Mountain athletes depend on a real heart rate input more than cyclists do, because the mountains do not give us a clean output metric. Cycling power is one of the cleanest measurements in endurance sport because the production is repeatable. The same wattage feels roughly the same three weeks running, which is what lets a cyclist triangulate: when heart rate looks strange, power says whether the strangeness is in the body or in the sensor.
The mountains do not offer that. Pace means very little in steep terrain, and vertical speed varies with snow, terrain, pack weight, environmental conditions, and technical difficulty. What we work with instead is the triangulation of pace, heart rate, and rate of perceived exertion. Heart rate carries more of the load for us, which makes the sensor on the back of the wrist the weakest link in the measurement.
Heart rate is also reading more than effort, and using it well means knowing when the number is telling you about something other than the session. It tends to run higher at a given effort when you are dehydrated, hot, at altitude, short on sleep, or fighting an illness you have not noticed yet, and in many athletes it sits slightly higher through the luteal phase of the menstrual cycle, with individual variation wide enough that your own pattern matters more than the population one. A heart rate you cannot drive upward at all can also point to fatigue rather than fitness.
This is the single most important thing to get right in the stack. For an athlete working close to the aerobic threshold, and particularly for one whose aerobic base has fallen behind their top-end fitness, a real heart rate input is the piece of equipment the whole approach rests on. It is also what makes the Continuous AeT reading in the Training Groups dashboard usable, since that reading is only as good as the heart rate data feeding it. An arm band or chest strap gives it something to work with. An optical wrist sensor does not.
Chest strap or arm band: which heart rate monitor is more accurate?
Both are accurate to use in training, while chest straps remain the reference standard, reading the heart’s electrical signal directly in the way an ECG does and agreeing with reference measurement at about 0.996, where 1.0 is perfect agreement. Arm-mounted optical bands such as the Polar Verity Sense and Wahoo TICKR FIT test within roughly ninety-one percent of that, with a real comfort advantage. For most athletes, the right choice is to use the option that you will actually wear.
Chest straps, most commonly the Wahoo TICKR, Garmin HRM-Pro, and Polar H10, are accurate, durable, and relatively inexpensive. They are also uncomfortable enough that plenty of athletes who buy them stop wearing them on long days, and a chest strap living in a drawer is less useful than an arm band on your bicep.
Arm-mounted monitors use the same optical sensing a watch uses, in a location where the band holds more reliably against thinner, more vascular skin. Independent testing has them tracking chest straps closely under most conditions, with the largest divergences during rapid heart rate transient in very short intervals. One placement detail is worth getting right: rotate the band so the sensor sits on the inside of your upper arm rather than the outside, where the skin is thinner and the vessels closer to the surface.
For many mountain athletes, an arm band is a practical choice for most sessions. For VO2max work, very short intervals, or data you intend to treat as laboratory grade, a chest strap is worth the discomfort. If you are training seriously and own neither, that is the first gap to close.
The limitations of an optical wrist sensor
For resting measurements and daily-life data, the sensor on your watch is usually fine. For training, it is not. Wrist-based optical sensors lose accuracy under the conditions mountain athletes train in: motion, arm loading, and rapid changes in heart rate. The error increases as the work gets harder.
The sensor sits against a part of the body that moves and flexes throughout a workout, and it tends to lose or smooth the signal. Cleveland Clinic researchers, presenting at the American College of Cardiology’s annual meeting, put four wrist monitors against a four-lead ECG in fifty adults and found errors of plus or minus fifteen to plus or minus thirty-four beats per minute, worst on equipment that loads the arms.
That study is old enough now that the hardware has improved substantially, though the newest testing says the problem has not gone away.
Measured across rest, moderate work, and vigorous work, wrist monitors agreed almost perfectly with a chest strap at rest, then came apart under load: average error climbed to twelve and fifteen percent, with individual readings capable of missing by forty to sixty beats per minute.
Cold is the second problem. Chilled skin constricts the vessels at the surface of the wrist, and the optical signal the sensor depends on gets measurably weaker when that happens. Whether that shows up as a worse heart rate number in the field is less settled. A 2026 chamber study at ten degrees Celsius, about fifty Fahrenheit, found no significant accuracy loss across ten devices, though its subjects were walking on a treadmill, not skinning uphill in a January wind. Read cold as a reason to trust the number less, not as proof it is wrong.
The upshot of this is that wrist-born monitoring is fine for daily resting heart rate, sleep, and overnight heart rate variability. It is not fine for working near your aerobic threshold, and it is not fine for interpreting what a hard workout cost you.
Should you track sleep and heart rate variability?
Track both, and read them as trends rather than as daily verdicts. Sleep duration and quality across weeks tell you something real, while a single bad night tells you very little. Heart rate variability read as one morning number is noisy and easy to misread. Read against your own rolling baseline across seven to fourteen days, it is one of the earliest signals you have for accumulated fatigue, incoming illness, and stress arriving from outside training.
It is worth knowing what these devices actually measure, which is movement, a heart rate proxy, and sometimes skin temperature, rather than sleep architecture directly. The stages your app reports are inferred. Duration and consistency are the parts of the sleep data worth trusting, and both are useful.
Heart rate variability reflects how your body is responding to stress rather than what you are capable of, and an athlete with a low reading can still complete a hard workout. The question it answers is not whether you can train hard today, but whether your body will absorb a hard stimulus productively today, or whether the same session lands as more accumulated stress.
Marco Altini, who has done as much as anyone to move heart rate variability from a laboratory metric to a usable training tool, gives two frames worth keeping. Read your own pattern against your own baseline rather than against population norms, since two athletes can sit forty milliseconds apart and both be at their personal normal. And treat single days as noise: measure consistently, at the same time, in the same body position, and read the trend across a week or two. One low morning is not a reason to change a plan. Three or four in a row against your own baseline is a signal worth heeding.
For menstruating athletes, at the population level, heart rate variability tends to run lower and resting heart rate slightly higher through the luteal phase than the follicular phase, and sleep quality tends to dip toward the end of the luteal phase. Two qualifications matter as much as the pattern. Individual variation is larger than the difference between groups, and the same athlete can show different patterns from one cycle to the next as symptoms, training, and outside stress all move. The physiological shift also does not reliably predict a performance shift, and studies that measured both have found resting physiology moving across the cycle while performance held steady. Track the raw numbers and read them against a cycle-aware baseline of your own rather than against a device’s composite readiness scoring, which will otherwise flag half of every month as a problem when nothing is wrong.
Should mountain athletes use a continuous glucose monitor?
A separate caveat matters for athletes with a flagged A1C. A 2025 Mass General Brigham analysis of nearly a thousand adults wearing continuous glucose monitors found that the link between monitor glucose and A1C held in people with diabetes, weakened in people with prediabetes, and disappeared entirely in people without diabetes. The two numbers are not measuring the same thing. Your monitor reports the glucose in your blood over the past two weeks. Your A1C reports how much of that glucose stuck to your red blood cells, which depends on how long those cells have been alive. In hematologically normal people, average red cell age ranges from thirty-eight to sixty days, and researchers have modeled that this spread alone can produce three different A1C results in three people with identical glucose control.
Endurance training is one of the things that changes red cell turnover. What that does to an athlete’s A1C specifically has not been studied, so treat it as a reason for caution rather than an explanation you can lean on. If your A1C comes back flagged, that number may be telling you something about your metabolism or something about your red blood cells, and a glucose monitor alone will not tell you which.
When is a pulse oximeter useful at altitude?
A pulse oximeter is useful when you are acclimatizing at altitude or running a structured hypoxic protocol. Read it as a trend across days, alongside resting heart rate and how you actually feel, rather than as a single morning number to act on.
A pulse oximeter measures the percentage of hemoglobin saturated with oxygen, reported as SpO2, and a healthy person at rest at sea level usually reads between 96 and 99 percent. Saturation falls at altitude, and the pattern of recovery across days of acclimatization is one of the clearer signals available to an athlete going high. A morning reading taken consistently, under the same conditions each day, tracks acclimatization in a way subjective feel does not.
Be careful with the saturation decision matrices that circulate in altitude-tent communities, the ones that tell you to raise simulated altitude above one number and lower it below another. Those figures come from equipment manufacturers rather than from published research, and we could find no peer-reviewed protocol that uses absolute saturation as the control variable. Another issue is that many consumer oximeters are not calibrated to read accurately below about 90 percent, which is precisely where those rules place their stop signals. A protocol whose stop signal sits inside its instrument’s error band is not much of a protocol. A more defensible read combines a low saturation with a resting heart rate that has climbed more than about ten percent above your own baseline, along with how you are sleeping and how you are recovering from sessions.
Most modern watches include wrist-based pulse oximetry, and the caveats that apply to wrist-based heart rate apply here as well. A dedicated finger oximeter is inexpensive and worth carrying on any trip where altitude is a real variable. For athletes neither at altitude nor in a hypoxic protocol, daily pulse oximetry is not a useful training tool, because normal variation in the measurement is larger than any training signal it might carry.
Is respiratory rate worth watching?
It’s worth watching, but not worth buying a device to track – yet. Respiratory rate sits at the early end of the adoption arc. The sensors are improving, the underlying signal is real, and the training applications are still being developed.
The physiology is what makes the category interesting. Breathing is a more honest cost signal than heart rate, which is distorted by heat, dehydration, caffeine, cycle phase, and illness. Respiratory rate is less affected by most of those. At altitude in particular, where heart rate becomes less reliable and the body’s primary response to hypoxia is to breathe harder, respiratory rate can read the cost of the work better than heart rate does.
The forward-looking hypothesis is that minute ventilation could serve as a pace-independent, fatigue-resistant signal of how hard the body is actually working, something closer to what power gives cyclists. The consumer devices are not yet refined enough to coach from on their own. For now, watch respiratory rate as a leading indicator alongside heart rate during altitude acclimatization, and the newly-released Tymewear chest sensor that tracks both heart rate and ventilation is one to watch.
Readiness scores are an opinion, not a measurement
The inputs underneath the score, meaning resting heart rate, heart rate variability, and sleep, are real signals worth reading as trends. The composite score built on top of them is weakly validated and correlates inconsistently with how athletes report feeling.
Readiness, recovery, and training-readiness scores are constructed metrics. A 2025 review catalogued fourteen of them across ten manufacturers, including Garmin, WHOOP, Oura, Polar, Coros, and Suunto. Heart rate variability fed eighty-six percent of them and resting heart rate seventy-nine percent, but the manufacturers disagreed on what window of data to use and how to weight it, and not one disclosed its formula. Few offered any published validation.1 There is also no agreed reference standard for readiness itself, so even a well-built composite can only ever be checked against proxies.
What happens when someone checks is instructive. Researchers followed twenty-three NCAA Division 1 swimmers through a heavy training block wearing WHOOP and set the data against a validated stress and recovery questionnaire. The underlying metrics behaved sensibly. Heart rate variability tracked both sport-specific stress and total stress (r = -0.46 for each), and in the male swimmers resting heart rate tracked general stress (r = 0.75). The recovery score assembled from those same inputs correlated with none of the four measures, with coefficients between -0.05 and 0.06.2 The parts carried signal. The number on the screen did not.
There is a deeper problem than validation, which is what the composite cannot see at all. On any given day, the most common limiter for an endurance athlete is muscular soreness from yesterday’s work, and no consumer device measures it. A score presented as a complete picture of readiness quietly hides the fact that a major input is missing from it. That is the argument for breaking the score apart, reading the components, and setting them against your own report of how you feel.
Why will two devices give different numbers for the same workout?
No two sensors read the same physiological event identically, and the gaps are large enough to change decisions. A chest strap and an arm band usually agree within a beat or two. A chest strap and a wrist sensor during a hard interval can disagree by twenty beats or more. Two pulse oximeters on the same finger can differ by a point or two. Two continuous glucose sensors on the same arm can differ by ten to fifteen milligrams per deciliter. This is not a reason to distrust your data. It is a reason to know which comparisons are valid.
A heart rate trend tracked on the same arm band for six months is valid, because the band is reading itself against itself. A trend that switched from a wrist sensor to a chest strap halfway through is not, because the change in the number reflects the change in the sensor rather than a change in you. If you switch sensors, start a new baseline and note it in your log.
Context shapes every reading. Heart rate variability trends lower through the luteal phase. Sleep shortens with travel across time zones. Saturation falls at altitude and moves with cold-driven peripheral vasoconstriction. Glucose responds to carbohydrate intake, exercise intensity, sleep debt, and a long list of variables that have nothing to do with metabolic health. Reading a measurement without reading the backdrop generates false signals.
Consistency is what turns measurements into a trend. Morning heart rate variability measured in bed at 6:30 is a different measurement from the same reading taken standing in the kitchen at 7:15. Discipline in how you take the reading is worth more than the price of the device taking it.
When the device and your body disagree, investigate the disagreement rather than defaulting to either one. Sometimes the device is right and you are underestimating your fatigue. Sometimes you are right and the sensor slipped, the night was cold, or the strap sat wrong. A reading that says recovered on a morning you feel wrecked is not permission to train hard.
Where your training data should live: TrainingPeaks
TrainingPeaks is the closest thing to a common language the coaching world has settled on, and most credible coaching tools, ours included, connect to it. The question worth asking about any platform is whether it adds numbers or adds clarity.
Ecosystem lock-in is the part athletes tend to discover late. Data that lives inside a manufacturer’s app in that manufacturer’s format may not travel with you when you change watch brands, which is one more argument for keeping the record that matters in a platform built for training rather than for hardware.
The Uphill Athlete dashboard we use in our Training Group exists to interpret rather than to duplicate. The raw data stays where it already lives. What the dashboard adds is a read on three questions: what should I do now, what is the highest-leverage part of my training to improve, and am I getting fitter? For athletes in Training Groups, it carries a Continuous AeT reading, which keeps your aerobic threshold current from the training you are already doing rather than waiting for the next scheduled test. The standard we hold it to is the one we would apply to any device: you should be looking at fewer numbers after adding it, not more.
The tech that is not worth buying
The stack matters as much for what it excludes as for what it includes. Substrate utilization scores from consumer devices do not earn a place, because the real measurement requires expired-gas analysis and the consumer approximation is not reliable enough to act on. Composite readiness scores used as a daily decision input do not, for the reasons above. Recovery boots and percussive massagers are rarely harmful and rarely load-bearing, and the money is almost always better spent on sleep, food, and coaching. A second watch bought for more data is buying anxiety, and a heart rate band is the better addition. Daily-wear glucose monitors without specific questions attached are expensive and noisy as a default state. And three apps reading your readiness off the same underlying data give you three opinions rather than three readings, so pick one and learn to read your own trend in it.
Roughly a third of consumers who buy a wearable stop using it inside a year. Less equipment, used more intentionally, tends to produce better training than more equipment read in passing.
Start from what you already own
If you own a Garmin Fenix, Forerunner, or Enduro, or a Coros Apex or Vertix, you have the watch you need, and adding an arm band completes the stack. An Apple Watch is a capable daily-life device but not the right primary watch for mountain training, because battery life and barometric altimeter performance are not in the same class as the dedicated units. A WHOOP or an Oura ring is good for sleep and heart rate variability trends and does not substitute for a GPS watch with an altimeter or for a heart rate sensor at intensity, so pair it with both and let the ring become your recovery layer while the watch and heart rate input become your training layer.
If you own nothing yet, buy the GPS watch first, add the heart rate band within a month, and buy nothing else for six months. Spend that time learning to read what those two produce.
From data to decisions
The stack does not coach the athlete. The stack produces data. The translation from data into training decisions is the actual work, and it is the part almost every athlete underestimates.
The athletes who get the most out of any tech stack are the ones whose own sense of their body stays the primary signal, with the data serving as confirmation, calibration, or challenge. The devices will keep getting better and the principles for using them well will not change much. An athlete who reads production, cost, and subjective sense together, knows the limits of each, and stays with one stack long enough to learn it will be ahead of the athlete who chases the next device.
For athletes who want structure around this, our Training Groups provide training plans, access to a community of mountain athletes, and a dashboard that keeps your aerobic threshold current from the training you are already doing. For athletes who want more targeted training guidance and data decisions made with them for a specific event or training cycle, one-to-one coaching is the right next step.
Sources:
Accuracy of Wrist-based Heart Rate Monitors
Gillinov S, Etiwy M, Wang R, et al. Variable Accuracy of Wearable Heart Rate Monitors during Aerobic Exercise. Medicine & Science in Sports & Exercise. 2017;49(8):1697-1703. Presented at the American College of Cardiology 66th Annual Scientific Session, March 2017.
Moghaddam M, Collins JP, Gardner CE, Rabel MC. Impact of Anatomical Placement on the Accuracy of Wearable Heart Rate Monitors During Rest and Various Exercise Intensities. Sensors. 2026;26(1):176.
Jung S, Thomson S, Pantelopoulos A, et al. Differential Sensitivity of Impedance Plethysmography and Photoplethysmography Sensors to Temperature-Induced Peripheral Vasoconstriction. Scientific Reports. 2026.
Gielen J, Van Oost CN, Debard G, et al. Accuracy of Optical Heart Rate Measurements for 10 Commercial Wearables in Different Climate Conditions and Activities. JMIR Formative Research. 2026;10:e85186.
Continuous Glucose Monitors
Rodriguez JA, Palermo NE, Song W, et al. Diabetes Technology & Therapeutics. Published online October 1, 2025. doi:10.1177/15209156251379506
Cohen RM, Franco RS, Khera PK, et al. Red cell life span heterogeneity in hematologically normal people is sufficient to alter HbA1c. Blood. 2008;112(10):4284-4291.
Smith JA. Exercise, training and red blood cell turnover. Sports Medicine. 1995. PMID 7740249.
Readiness Score
https://marcoaltini.substack.com/p/paper-readiness-recovery-and-strain
Doherty C, Baldwin M, Lambe R, Burke D, Altini M. Readiness, recovery, and strain: an evaluation of composite health scores in consumer wearables. Translational Exercise Biomedicine. 2025;2:128-144. doi:10.1515/teb-2025-0001
Lundstrom EA, De Souza MJ, Koltun KJ, et al. Wearable technology metrics are associated with energy deficiency and psychological stress in elite swimmers. International Journal of Sports Science & Coaching. 2024;19(4):1578-1587. doi:10.1177/17479541231206424