I started getting interested in bikes when I was 13. My interest has waxed and waned over the years, but never really went away. I’ve thought of myself as a cyclist since I got my first pair of cleats at 17. I’ve always been interested in bikes as objects of technology and craftsmanship, and I’ve always enjoyed riding them. At various points I’ve gotten to be a pretty strong rider, but I’ve never been methodical about it—beyond following Eddy Merckx’s advice to ride lots, and perhaps alternating long days with short days, I’ve never been interested in structured training. Lately I have gotten interested, and like so many things, once you pry the lid open on a subject, you discover it goes much deeper than you ever imagined.

I’ve been trying to digest a lot of the concepts involved in structured training, but I haven’t found any one place that packages them up so far. There is a book (and a paper that preceded it) that, well, “wrote the book” on a lot of this, and I may eventually break down and get it. For now, this is my own cheatsheet. Some of this may be wrong. I’m not going to link back to citations for everything. Caveat lector.


Watt
The unit of measure for power. Training these days is structured around power and heart rate. In the past, cyclists would ride to time, or to distance, or to speed.
Kilojoule
The unit of measure for total work performed during a workout. Note that watts are a measure of instantaneous power, but kilojoules are a measure of work over time (same as watt-hours: there are 3600 joules in 1 watt-hour). Thanks to a statistical fluke, the work performed in kilojoules is treated as equal to the calories burned during a workout. So you burn 1000 kCal in a 1000 kJ workout.
Functional threshold power (FTP)
The maximum average effort a cyclist can put out for one hour, measured in watts. The gold standard for this is to ride an hour all-out. Most people don’t do this because it’s awful—instead, most people ride a 20-minute FTP test and deduct a certain percentage from that result—typically 5%, but if you’re not exceptionally fit, it should be 10% or 15%. Even riding 20 minutes on the road is difficult just for logistical reasons—you’d want 7 or more miles of level road with no stops, or a hill climb that’s a few miles long, again without stops—so I suspect most people do FTP tests on stationary bikes. FTP is a training tool: it’s used as a baseline for other workouts. All my interval patterns are based on percentages of FTP. It’s also good for bragging rights (unless your FTP is as low as mine, in which case you prefer not to talk about it). I’ve seen articles on how to maximize your FTP test results, but this seems wrong-headed if you’re using it as a training tool, since all the training you base on it will be off. The most celebrated record in cycling is the hour record, which is pretty much what it sounds like: how far you can go in an hour (on a track bike, in a velodrome). The current men’s record for this is about 55 km, and it’s estimated that riders are putting out about 440 watts at that level (which sounds less impressive when you realize it’s about 3/5 horsepower—less than a chainsaw engine puts out).
W/kg
Your power-to-weight ratio. Usually refers to Your FTP divided by your weight, but may be used to describe the power you can maintain over shorter periods. A small, strong rider will have a better power-to-weight ratio than a big rider who’s not so strong, but the big rider may have a higher absolute wattage output. These numbers can be important in different contexts: riding fast over level ground is mostly a matter of raw power because once you get past about 16 mph, almost all the drag you encounter is aerodynamic drag, and that increases with the square of your speed. But riding fast up a hill is more about W/kg, because you’re going slower in the first place (so aerodynamics are less important) and gravitational drag becomes a big part of the total resistance you encounter.
Critical power
The maximum power that can be maintained indefinitely, in watts. You can put out higher power, but only for a limited period of time, and there’s an asymptotic curve plotting the relationship between power output and duration, so you can put out very high power for a few seconds, fairly high power for a few minutes, and critical power for hours. Going beyond CP means relying to some extent on anaerobic capacity.
W’ (w prime)
The capacity for work above critical power, in kilojoules. You can put out effort in the W’ range for 10–15 minutes. The problem with going into the W’ range is that it costs a lot of energy, and once you’re done, you’re very depleted.
Normalized power
This is a weighted average power for a workout. Because all the time you spend above critical power tends to burn you out more quickly, a workout in which your effort fluctuates between high and low levels will be harder than a steady-state workout at the same average power. Normalized power reflects that.
Intensity
Normalized power divided by FTP.
Training Stress Score (TSS)
This is way of expressing a workout’s duration and intensity. Riding for one hour at FTP will have a TSS of 100. This is used to set weekly training goals, so for example you’ll aim for your all your workouts in a week to add up to a TSS of, say, 350.
Chronic training load (CTL)
Average TSS over 42 days.
Acute training load (ATL)
Average TSS over 7 days.
Training stress balance (TSB)
CTL minus ATL. I’ve also seen this referred to as “form.” The idea is that you want to be fresh for big events, so you taper off your training in the days beforehand. This metric is used to optimize your tapering.
Heartrate (HR)
Everyone has a maximum heartrate that’s estimated based on age, and heart-rate zones are all calculated based on your max HR. I’ve seen 220 minus age (for men) and 226 minus age (for women) as the most common way to compute this. Going by this, my max HR is 166 (as of this writing). I’ve also seen 208-(0.7 × age), which for me winds up being a few bpm higher (the results from these two equations match for men when they’re 40, for women when they’re 60). I’ve pushed myself to 165 bpm during workouts and held it steady there for a minute or two, so I’ll call these formulas close enough for me. Resting heart rate can improve dramatically with exercise. Four-time Tour de France winner Miguel Indurain was reputed to have a RHR of 26 bpm in his prime.
Zone
Can refer to heart-rate zones or power zones. Anyone who has used a fitbit with heart-rate monitoring has seen the yellow/orange/red zones. And it’s my understanding that the theory behind Orange Theory fitness boutiques is that they keep you in the orange zone. It turns out there are numerous different zone systems, with different numbers of zones and different breakpoints between them, and if you keep track of your data with more than one app/service, keeping their zones in alignment is a chore. Zones are another training tool, where you aim to keep your heart rate or power in a certain zone for a certain period of time during your workout.
Lactate threshold
A limit on sustained effort. Any effort beyond LT will basically be a sprint that can only be sustained for about 2½ minutes. This is really interesting to me. When I was younger, we thought of lactic acid as the waste product of exercise, and that lactic-acid accumulation occurred because your body was working too hard to clear it. Now we understand that lactate is part of the energy-transport system (also, we talk about lactate now, not lactic acid), and LT occurs because your body is producing it faster than it can process it. The body needs to deliver oxygen to the muscles in order to clear the lactate from them. We used to talk about the “anaerobic threshold,” that is, a level of intensity where you couldn’t get enough oxygen to your muscles to prevent lactic-acid accumulation, and to some extent, we still do, but nowadays we mostly talk about the lactate threshold to refer to the same idea. I get the impression this is because what we’re describing is the actual measured blood-lactate concentration. Apparently there are numerous ways to define LT, although the one I’ve seen used the most is where the lactate concentration is 4 mmol/l. This is also sometimes called LT2, to distinguish it from LT1, which is the point at which your body starts accummulating lactate faster than it can clear it (“onset of blood lactate accumulation” or OBLA). The effort in watts where LT1 and LT2 are reached can be measured, and obviously, the higher the wattage the better.
VO2max
The amount of oxygen you can breathe in per minute, in units of ml/min (sometimes expressed relative to body weight, ml/min/kg). The gold standard for testing this is to exercise to exhaustion while wearing a mask that measures the volume of air you breathe, but it can be approximated based on max and resting HR, or heart rate after specified exercises. There’s obviously a relationship between VO2max and LT, and LT is generally estimated to occur at 50–60% VO2max for untrained athletes, and 70–80% for highly trained athletes.
Intervals
A workout where you alternate periods of high intensity with low intensity.
HIIT
High-intensity interval training. A style of intervals where you ride close to VO2max with relatively long “on” intervals.
Sprint intervals
A style of intervals where you ride beyond VO2max with short “on” intervals.
Polarized training
An approach to training based on long periods at low intensity and short periods at very high intensity. The balance can be in the range 85/15 to 95/5. The idea is that you spend all your time in Zones 1/2 or 5, and none in Zones 3/4 (assuming you use a 5-zone system)—or that you simplify your zones to “easy/no-mans-land/hard.”
Threshold training
The opposite of polarized training: spend all your time in Zones 3/4. There seem to be different definitions for this (just as there are different definitions of zones), but the general idea seems to be steady-state training at 75–90% of FTP. Current scholarship seems to be that polarized training gets results faster, but threshold training has a lot of adherents.
Sweetspot training
Same as threshold training
Moderate intensity continuous training (MICT)
Same as threshold training
High-volume training
Long miles at low intensity. Also called “base mileage.” My understanding is that you’re supposed to have a lot of base mileage before you attempt higher-intensity training.
Cadence
Pedal speed, measured in rpm. Most experienced road cyclists aim to keep their cadence around 80–90 rpm. There’s evidence that lower cadences are more energy-efficient, but it’s easier to produce more power at higher cadences.
Bike computer
Also called a “head unit.” Bike computers used to just compute riding time, speed, and distance, and if you were really fancy, you got one with a barometric altimeter. Those still exist, but these days, fancier ones are tantamount to smartphones (many of them run the Android OS), and connect to a constellation of other devices.
Heartrate monitor (HRM)
There are two types: the traditional chest strap, which monitors the electrical activity in your chest muscles, and the newer optical type, often built into a watch or armband, which visually detects the changes in your veins as blood flows through (word of the day for this: photoplethysmograph). Chest straps are usually cheaper and have longer battery life. Some of the optical ones can also work as pulse oximeters.
Power meter
A meticulously calibrated strain gauge applied to a part of the bike’s drivetrain (pedals, crankarms, crank spider, rear hub) that transmits its readings to a bike computer. Although they’re coming down in price, power meters are still really expensive, and add at least $200 to the price of whatever part they’re attached to. Having a power meter on the bike has transformed competitive cycling, as racers know how much power they can put out for how long, and don’t make heroic-but-doomed breakaways.
Smart trainer
An old-fashioned stationary trainer would usually let you vary resistance manually, but did not calibrate this beyond “easy” to “hard.” A smart trainer uses computer control to apply resistance, and can measure power reliably. Smart trainers can use smartphones or bike computers as their controllers and front ends.
Golden Cheetah
Freeware analytic software. I first downloaded it about four years ago, and was so confused by what I was seeing that did not look at it again until last week. I still don’t understand half of what’s going on in there, but I’ve got a little bit of a handle on it.

Formulas for various concepts