77 Watts at 135 Beats: Why Cycling Power Measures Altitude Better Than Running Pace
Ladakh field log · Day 4
Yesterday I told you a faster run was not proof of anything, because the route was flatter and I had worked harder. Today I have a number that cannot make those excuses. Seventy seven watts, at 135 beats per minute.
Day four in Leh. I rode in the morning, partly to take the impact out after two consecutive running days at altitude, and partly because a bike carries an instrument my running shoes do not. Then I ran again in the evening, which turned out to be the more interesting half of the day.
That instrument turns out to answer the question this whole series is built on far better than pace ever will. And the evening run showed me the cost of not listening to it.
Why this matters more than yesterday's pace: a watt is a watt on any hill, in any wind, on any surface. Power cannot be flattered by a downhill or ruined by a headwind. It is the honest measure of work performed.
Why Power Beats Pace at Altitude
In yesterday's log I published two runs one day apart and showed that a one minute fifty six second per kilometre improvement was mostly a flatter route and a harder effort, not adaptation. That was an honest correction, but it exposed a real problem with running as a measuring tool.
Pace is not a measure of work. It is a measure of work divided by everything else. Gradient, surface, wind, temperature, shoes, how you slept. Change any of them and the number moves without your fitness moving at all.
Power is different. A power meter measures the actual force you apply to the pedals and the speed at which you turn them. Ride uphill, ride into a headwind, ride on gravel: 77 watts is still 77 watts. The environment cannot inflate it or deflate it.
The Full File
| Metric | Reading | What it tells you |
|---|---|---|
| Distance | 13.65 km | In one hour and one minute |
| Average speed | 13.3 km/h | Slow, deliberately |
| Average heart rate | 135 bpm | Easy aerobic, same band as yesterday's run |
| Average power | 77 W | The headline number |
| Normalised power | 98 W | Adjusts for how variable the effort was |
| Intensity factor | 0.54 | Comfortably an easy session |
| Efficiency factor | 0.57 | Watts per heartbeat. My baseline. |
| Variability index | 1.27 | The effort was choppy, not steady |
| Elevation gain | 265 m | A net climb from Choglamsar up to Leh |
| Torque effectiveness | 73 to 79% | How much of each pedal stroke did useful work |
| Training load | 32, low | A genuinely light session |
| Conditions | 10°C, 65% humidity, 7 km/h wind | Cold morning, near still |
What 77 Watts at 135 Beats Actually Means
Some context on that number. Seventy seven watts is not training. At sea level, for a trained endurance athlete, it is the power you produce while chatting on a flat road, or spinning your legs out the day after a race. It is close to the lowest meaningful output a bike will record.
My heart rate sat at 135 beats per minute to produce it.
For comparison, yesterday I ran at 138 beats per minute. Almost the same cardiac cost, on a session that produced a fraction of the mechanical work. My heart is doing normal aerobic labour to support an output that would barely register at sea level.
That is the same dissociation between effort and output I described in the running logs, but stated in a unit that leaves no room for argument. There is no hill to blame and no headwind to blame. There is simply less oxygen arriving, so less work gets done for the same effort.
Efficiency Factor, and the Test I Am Running for Eight Weeks
Efficiency factor is a simple idea. Take your average power and divide it by your average heart rate. It tells you how many watts each heartbeat is buying you.
Mine today was 0.57. Seventy seven watts, 135 beats.
If altitude adaptation does what it is supposed to do, that number should climb over the coming weeks. More oxygen carried per unit of blood means more power available at the same heart rate. The heartbeat stays constant and the watts go up.
- The same test, weekly. Forty five to sixty minutes on the bike, heart rate held in the same band, as steady as the road allows.
- One number published each time. Efficiency factor, alongside the raw power and heart rate it came from.
- Baseline set today at 0.57. That is the line everything after this is measured against.
- Published whether it rises or not. If it flattens or falls, that goes up too, with what I think went wrong.
That is the whole experiment, and it is deliberately boring. One metric, one protocol, repeated. Anyone can check the arithmetic.
And Then I Ran in the Evening
Ten hours after the ride, at 6:39 PM, I went out for a short run. Twenty eight minutes, three kilometres, nothing ambitious.
It was the most useful data I collected all day, and not because it went well.
| Metric | 27 July, 6:08 PM Chuchot Yakma, flat | 28 July, 6:39 PM Murtse road, climbing |
|---|---|---|
| Average heart rate | 138 bpm | 148 bpm |
| Average pace | 8'48" per km | 9'24" per km |
| Running efficiency | 95% | 84% |
| Distance | 6.81 km | 3.01 km |
| Duration | 1:00:00 | 28:17 |
| Elevation gain | 20 m | 42 m |
| Training load | 81 | 53 |
| Conditions | 19°C | 14°C |
Two different roads, at almost the same time of evening, one day apart.
Ten beats per minute higher. Thirty six seconds per kilometre slower.
That combination is the one I watch for above all others. A rising heart rate on its own can mean many things. A slowing pace on its own can be the route or the weather. But heart rate up and pace down, together, usually means the body is paying more and producing less. It is often the first sign to appear before anything else goes wrong.
What the week actually looks like
| Day | Session | Training load |
|---|---|---|
| Day 2, 26 July | Easy run, 5.59 km | 58 |
| Day 3, 27 July | Zone 2 run, 6.81 km | 81 |
| Day 4, 28 July, AM | Easy ride, 13.65 km | 32 |
| Day 4, 28 July, PM | Easy run, 3.01 km | 53 |
That is four sessions in three days, on days two through four at 3,500 metres, with day four carrying a combined load of 85, the heaviest of the week.
- Take tomorrow off. The evidence here is suggestive rather than conclusive, but a rest day is the cheapest possible response to an ambiguous fatigue signal, and it costs almost nothing.
- Fix a test route and stop guessing. Two days running, I have compared runs on different roads and had to caveat the answer away. One flat route, one time of day, one heart rate ceiling. Until that exists, none of these running comparisons will mean much.
- Double sessions do not belong in the first week at altitude. Aerobic volume is fine. Stacking it into one day buys very little and costs recovery you have not yet earned.
- Four sessions in three days on days two to four is more than our residential protocol allows. Our group rests on days one and two, trains short on day three, and never doubles in week one.
- I am not following my own protocol. I have the altitude history to make that call for myself, and I said so in the first log in this series. It is still worth naming plainly, because a reader should not copy this pattern.
I am publishing this because it is exactly the kind of day most coaches quietly leave out. The morning ride was clean and controlled and made a nice headline. The evening run was the one that actually taught me something.
Where This Measurement Is Weak
Three things you should know before you put weight on that 0.57.
Today's ride was not steady
My variability index was 1.27, which means normalised power sat well above average power. In plain terms, the effort was choppy rather than smooth, which is what happens riding a highway with traffic, junctions and a net climb. Efficiency factor is most reliable on steady efforts. Future tests need to be smoother than this one, and I will say so each time if they are not.
Heart rate drifts for reasons that are not fitness
Sleep, hydration, heat, caffeine and accumulated fatigue all move heart rate around. A single week-to-week change in efficiency factor could be any of those. Only a trend across several weeks means anything, which is exactly why I am not going to make claims from the second data point.
Adaptation on the bike is not the same as running faster
Even if the number climbs, that shows a physiological change, not a race result. The most cited research on altitude training found athletes who lived and trained high gained the blood adaptation and still did not run faster, because training quality at altitude is degraded [2]. A rising efficiency factor is evidence of adaptation. It is not a promise of performance.
Riding at Altitude, Practically
- Ride by heart rate or power, never by speed. Your speed will be poor and it means nothing here.
- The morning is cold. It was 10°C at 8:11 AM in late July. Layer properly, and expect your hands to suffer before the rest of you does.
- Everything is a climb somewhere. Today gained 265 metres across 13.65 kilometres without feeling like a mountain route. Plan for that.
- Traffic on the main roads is real. Choglamsar to Leh is a working highway, not a training loop. Ride early.
- Cycling is a useful way to keep aerobic volume while sparing your legs in the first weeks, when running impact and altitude fatigue stack up quickly.
- The 48 hour rule still applies [1]. Do not arrive and ride on day one because the effort feels controllable.
Frequently Asked Questions
Does altitude affect cycling power?
Yes, substantially. Less oxygen is available per breath, so less energy can be produced aerobically, and power output at any given heart rate falls. On day four in Leh I averaged 77 watts at 135 beats per minute, a heart rate that would normally support considerably more power at sea level. The effect is largest in the first weeks and eases as you adapt.
Is power or heart rate better for training at altitude?
Use heart rate to set the effort and power to measure it. Heart rate tells you how hard your body is working, which is what you want to control at altitude. Power tells you how much work actually got done, which is what you want to track over time. Speed is the least useful of the three up here.
What is efficiency factor and why does it matter at altitude?
Efficiency factor is average power divided by average heart rate, so it describes how many watts each heartbeat produces. It is useful at altitude because it is not affected by gradient, wind or surface. If it rises over weeks while your heart rate protocol stays the same, that is meaningful evidence of adaptation. Mine was 0.57 on day four.
Why is power a better measure than pace at altitude?
Because pace is affected by gradient, surface, wind and temperature, while power is not. A watt is the same amount of work whether you produce it uphill or on the flat. If you want to compare two sessions weeks apart and draw a conclusion about your body rather than about the road, power is the far cleaner instrument.
How long does it take to adapt to cycling at high altitude?
Early changes in the first days are largely ventilatory and modest. Meaningful increases in oxygen carrying capacity develop over weeks. Most people should expect their power at a given heart rate to remain well below sea level values for the first two weeks, with gradual improvement after that, and considerable variation between individuals.
Should you cycle or run when acclimatising?
Both have a place, and cycling has one clear advantage in the first weeks. It lets you accumulate aerobic time without the impact loading of running, at a point when your body is already managing the stress of altitude. I ran on days two and three, and rode on the morning of day four for exactly that reason, before undoing some of the benefit with an evening run.
Can you do two training sessions in one day at altitude?
You can, but in the first week it is rarely a good idea. I rode in the morning and ran in the evening on day four, and the evening run came in ten beats per minute higher and thirty six seconds per kilometre slower than the previous evening's run, though on a steeper route. Aerobic volume is valuable at altitude. Stacking it into a single day costs recovery you have not yet earned, and our residential group does not double in week one.
How do you know if you are training too hard at altitude?
The most useful signal is a rising heart rate alongside a slowing pace on the same route at the same time of day. Either one alone can be explained by the weather or the terrain, and if the routes differ the comparison is weak. Watch also for a falling heart rate recovery, a rising resting heart rate, disturbed sleep, and appetite loss. No single reading is decisive. Look for several pointing the same way.
- All training figures in this log are from the author's own device files recorded on 26, 27 and 28 July 2026, using a COROS watch with a chest heart rate monitor, and a bicycle power meter for the ride. Raw activity screenshots are published alongside these articles.
- Levine BD, Stray-Gundersen J. "Living high-training low": effect of moderate-altitude acclimatization with low-altitude training on performance. Journal of Applied Physiology. 1997;83(1):102-112. Randomised controlled trial, 39 competitive runners. The live high, train high group gained red cell mass and VO2max but no improvement in 5 km time. PubMed
- Health advisory, District Administration Leh, Union Territory of Ladakh. All arriving tourists must complete at least 48 hours of acclimatisation before travelling to higher altitude areas. leh.nic.in
Niraj Kumar Borah
Founder and head coach of Fitness Bootcamp, a residential health transformation programme running in Rishikesh, Ladakh, Manali, and the north east. Since 2020 he has guided more than 4,600 guests through structured, fully supported transformations.
He has spent four to six months of each year in Ladakh for several years, and has raced the Ladakh Marathon in 2023 and 2024. He is here from July to September 2026, running the routes and testing the acclimatisation protocol our residential group will follow from 16 August, and racing the 11.2 km on 13 September. He publishes his own training data daily, including the sessions that go badly.
- VDOT Certified Distance Running Coach · VDOT O2
- Certified Heart Rate Performance Specialist · NESTA
- Precision Nutrition Level 1 · Precision Nutrition
- Affiliated HYROX Performance Coach · verify on the HYROX register
- Mountaineering, Adventure Course · Jawahar Institute of Mountaineering, J&K
- Ladakh Marathon · 5 km 2023, 11.2 km 2024, racing the 11.2 km on 13 September 2026
- Full background and competition record · read here
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See the programmeThis log is general educational information about the physiology of altitude and training, and is not medical advice. Ascent to high altitude carries real medical risk, including acute mountain sickness and, rarely, high altitude pulmonary or cerebral oedema, which are emergencies. If you have any cardiovascular, respiratory, or haematological condition, are pregnant, or have a history of altitude illness, please speak with your doctor before travelling to altitude. Individual responses vary considerably, and the readings published here are one person's and should not be used as a benchmark for your own. Figures were recorded on 28 July 2026. If you believe any figure here is inaccurate, please contact us with the source and we will correct it.
