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Comment by qwertox | Hacker News Reader

When I do sports (riding bike every day for at least one hour in mostly anaerobic mode) after not eating for at least 18 hours or so (which I don't do often), I feel like I've got unlimited resources of energy available.

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Color me skeptical. In the anaerobic zone you're going to be at something like 90% of max heart rate and getting almost all of your energy from carbohydrate stores. Most people deplete those in less than an hour, especially when fasted.

When I'm following a polarized training program I find I can do the long, slow aerobic workouts just fine when fasted. But when doing high intensity anaerobic intervals I fall apart quickly if I haven't eaten some carbs before.

As a runner I was told that the liver holds about 600 calories of glucose, which would be roughly an hour of exercise. Though the body doesn’t run straight to the egde of zero glucose, I think it alters the fat/glucose ratio during the first hour of exercise and the 50/50 point is about 30 minutes. Obviously very roughly and assuming normal physiology but matches your experience.

The fat/glucose ratio depends on effort intensity and individual physiology. At very low aerobic intensities metabolically healthy people get most of their energy from fat. As intensity increases the mix shifts until you're burning almost 100% glucose and 0% fat near max anaerobic effort. This makes sense because fat metabolism requires more oxygen and you hit a limit on how much oxygen you can pull into your bloodstream. Once stored glucose is depleted then either you need to consume some carbs, or drop the intensity way down. The point at which that happens varies widely based on multiple variables.

I must add to this that I'm a bit overweight, since I don't do any upper body training. I have a BMI of 28 with strong muscles in the legs and probably a good heart, but a lot of belly fat. My HRmax is usually a bit below 180, but definitely above 175, so I'm in anaerobic mode at above 145, where 150 to 160 is what I usually aim for, tending towards the lower limit.

My theory is that at this point I'm somehow just taking the energy out of the body fat, but I'm probably very wrong with this assumption.

Yes, your body is then running on fat via ketones.

I once did a 6 mile hike in (and up) weekend camping trip with just some salt for electrolytes and a pack of hotdogs.

As you're on a bike, it would be a lot better to get a power meter, take an FTP test and then ride 20% above your FTP to properly ride in an anaerobic zone. You'll quickly find that long anaerobic exercise isn't possible

Heart rate is too affected by other factors like hydration, temperature, stress etc to be reliable.

How do you ride bike in anaerobic mode consistently without going dangerously fast?

I've been looking for a device that makes pedaling heavier if activated but haven't found it yet.

A parachute?

The tachycardia experienced by skydivers isn't the same sort of stimulation that exercisers are looking for. But it's an interesting thought.

Hehe, not practical on my daily commute. It also doesn't work with strong tailwinds.

stationary bike. but keeping a top % hr for an hour straight is very impressive if true.

A dynamo connected to a resistance will do. An old bike had a dynamo connected to a rechargeable light, the bike felt heavier the more the battery depleted.

Alternatively get a Turbo trainer or rollers with resistance for stationary training. Lots of people love it but it's not for me, though rollers aren't bad but the it gets very hot even outdoors with a fan.

I investigated the dynamo solution, but it turns out that modern dynamos have a large airgap which ensures that you can only get a few watts of energy out of them (so you don't overload the lights).

Find a steep hill and you can pedal as hard as you like without going very fast. But in general there's nothing particularly dangerous about riding fast if you have decent bike handling skills and watch out for traffic.

Unfortunately, changing the route of my daily commute to one with more hills is not really an option.

Without hills the only way is to ride in a suburban or rural area. You can do 25-30mph safely for miles between lights there which, should be hard enough for most people. Big cities are fundamentally not safe serious athletic cycling, anaerobic or otherwise. At best you spike your heartrate sprinting between lights then stress your body with high HR waiting at a light. Or guys will do near 30mph in a paceline around Central Park and act offended when some tourist steps out in front of them.

Not consistently, but around 2/3 of the time. I'm usually on trails where there aren't many people and which I know well, so I can go full speed, which is between 30 and 40, rarely 50 kmh downwards. This is on a MTB with offroad tires, which kind of glues you to the ground.

These are the last 3 days https://imgur.com/a/MG7AlOw

Top is Thursday, middle Friday, bottom Saturday.

The lower part of the image contains a red line, which is my heart rate. You can dimly see a green and a red region, where red is anaerobic, the transparent area below it aerobic, the green area fat burning, the area above red is the warning zone above 90%.

The white and green line is the speed, where white is GPS-speed and green is a speed sensor on the wheel. Blue is the pedal cadence, apparently the battery is dying.

Black is GPS altitude, dotted black is barometer and magenta is environment temperature (an ESP32 with a Bosch sensor connected via BLE to the phone).

The first one was Thursday in the morning, because I had my second vaccine that afternoon.

The second one in the late afternoon because I wanted to wait as long as possible because of the vaccine. You can see in the white speed profile that I was doing the bedding-in of new break-pads while going down the hill. This was with another bike where apparently both the speed and the candence sensors are dead.

The third one was a longer ride today where I went up the mountain on the other side (shortly after 5pm) with an average speed of around 7 kmh climbing a height of 170 m. This was a total of 28 km in 1:30 h.

Maybe some kind of strong elastic band which you use to apply constant pressure on the brake lever(s)?

You can get an indoor trainer like a wahoo kickr which attaches to your back wheel.

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