Nearly every profession, sports, or area of study has its own language, and subsequently its own acronyms and abbreviations. Cycling training terms can sound like gibberish to non-cyclists, and can be confusing to long-time riders, too. Here’s a reference guide to some of the most common terms and abbreviations used in cycling training. And because definitions are not very useful on their own, we added context for how to use them.
Note: Several cycling training terms used throughout this post are trademarked by TrainingPeaks, including Training Stress Score®, Normalized Power®, and Intensity Factor®. Additionally, terms including Acute Training Load, Chronic Training Load, Training Stress Balance, and Efficiency Factor are featured in TrainingPeaks software. In some cases, metrics that represent similar concepts are used in other apps.
Acute Training Load (ATL)
Short-term average of daily training load, measured by daily TSS. The default in TrainingPeaks is a 7-day rolling average. ATL is typically considered a proxy for ‘fatigue’. Strava uses the term “Fatigue” to denote a similar concept, but it is based on “Bike Score”, which is comparable to but slightly different than TSS.
Anaerobic Capacity (AC)
Your anaerobic capacity is the amount of work you can perform at an intensity above lactate threshold power output. It is not your peak power output above lactate threshold power. Whether you perform a higher power but shorter effort, or a slightly longer effort at a lower power output, the amount of work you can do stays the same. In other words, a cyclist with a lactate threshold of 300 watts and an anaerobic capacity of 20 Kilojoules (the work they can produce), could us their anaerobic capacity for a 1000-watt sprint that lasts just under 30 seconds or a 500-watt effort that lasts 1:45. In order to produce 1200 watts for that 30-second sprint, or to maintain that 500-watt effort for 2 minutes, you have to increase anaerobic capacity.
Average Power (AP)
A simple measure of power output in Watts divided by time. AP includes data from each timestamp (depending on the sampling rate of a power meter), including coasting or measurements showing zero watts. All data points are weighted equally, meaning AP offers little insight into the variability (or steadiness) of an effort or ride. As a result, a steady moderate-paced ride and a high-intensity interval workout can have very similar APs.
Chronic Training Load (CTL)
Long-term weighted average of daily TSS. The default in TrainingPeaks is 42 days. CTL is often thought of as an athlete’s ‘fitness’, but this can be misleading. Although ‘high fitness’ might sound like you should be fast, a high CTL does not always indicate high performance. It may be better to think of it as ‘training workload you’ve been doing consistently’.
Chronic Training Load is very volume dependent, but it doesn’t tell you as much about the quality or specificity of the work. For instance, you can maintain a high CTL by riding moderate-paced endurance rides 6-7 days a week. Daily TSS will be stay pretty consistent, so the weighted average will stay pretty consistent. Or, you can achieve the same CTL by mixing endurance rides and structured intervals and taking 1-2 rest or recovery days each week. The first method lacks the specificity to improve performance and the rest necessary to make positive adaptations. The second method features days with higher TSS and rest days with zero TSS. The weighted average may be similar, but the performance outcome will be very different.
If you have a Strava membership, the “Fitness” line on the “Fitness and Freshness” chart is similar to CTL. It is calculated a bit differently, so don’t expect Strava and TrainingPeaks numbers to match.
If you want to learn more, take a listen to our podcast episode on CTL.
Efficiency Factor (EF)
Normalized Power divided by Average Heart Rate for a given duration. This can provide some insight on whether your fitness is improving. As you gain fitness, you should be able to produce the same NP at a lower average heart rate, or a higher NP at the same average heart rate. This indicates you have adapted to training and can now achieve a greater output for the same oxygen consumption.
One caution on EF is that it relies on Average Heart Rate, which can be affected by heat, hydration status, stimulants like caffeine, fatigue, and lifestyle stress. As a result, it is best to look at the trend of EF over time, rather than focusing on EF today vs. yesterday. Significant changes from day to day are more likely caused by aforementioned external factors.
Functional Threshold Power (FTP)
Functional Threshold Power is the maximum power you can theoretically maintain for 60 minutes. It is typically determined through one of three types of field tests: an 8-minute FTP test, 20-minute FTP test, or a Ramp Test. It can also be determined through analysis of accumulated power data. A rider’s FTP is then used in calculations that establish power zones for interval training.
FTP is not the same thing as Lactate Threshold. However, FTP testing is non-invasive, economical, and easily repeatable. And coaches can use FTP to predict power at lactate threshold when athletes cannot directly measure blood lactate during a test. From a practical standpoint, it determines the highest amount of work your aerobic system can sustain for prolonged efforts.
A high FTP indicates an athlete has a strong aerobic engine. That’s a good thing; it means you can perform a lot of work before blood lactate production exceeds your ability to process it and break lactate down to usable energy. One goal of endurance training is to increase ‘fractional utilization’, which is power at FTP as a percentage of power at VO2 max. If your fractional utilization is 80% during a 30-minute hillclimb today and (all else being equal) we improve fractional utilization to 85%, you should go faster.
On the other hand, a high FTP does not guarantee success in all cycling endeavors. Athletes who focus too much on developing power at FTP may have undeveloped fitness for short, high-power efforts like sprints and accelerations, or for 5- to 8-minute maximum intensity efforts that rely on power at VO2 max. As a result, many training protocols focus on building power at FTP and then shift to more event-specific training that leverages that power at FTP to achieve other adaptations.
Intensity Factor (IF)
The ratio of Normalized Power to Functional Threshold Power for a given ride, race, or segment. This is a way to quantify the intensity of a ride and allow for comparisons between rides. For instance, an easy or recovery ride would have an IF less than .65, or NP is 65% of FTP for that ride. An endurance ride is likely between .70-.80, an interval workout or group ride will often be .75-.85, and a ride close to an athlete’s FTP would have an IF of .90-1.0. Short, very high intensity workouts under an hour may be over 1.0. Note: These ranges are a bit lower than what is published on TrainingPeaks, but reflect what our coaches see in data files from amateur and masters cyclists.
When intensity factor is consistently high for day-to-day rides, it may indicate that a cyclist’s fitness has improved and it’s time to re-test for FTP. For instance, if you are completing 2-hour moderate-intensity endurance rides and they keep coming out at an IF of .90-.95, your FTP is likely set too low in your training software.
We calculate power output on a bicycle with the equation: Power in watts = Torque x Cadence. This is a cycling-specific version of the general equation Power = Force x Velocity. A kilojoule is unit of energy representing the work performed by producing watts in a given amount of time: Kilojoules = (watts x seconds)/1000. For example, riding at an absolutely constant 200 watts for 3600 seconds produces 720 kJ of work in an hour.
Kilojoules are an absolute measurement of work and can be used to evaluate energy expenditure. Athletes and coaches often use Kj to compare the energy demands of rides and races, or to manage dietary calorie expenditure and consumption. One food Calorie is equal to 4.184 kJ, and cyclists typically have a Gross Metabolic Efficiency of .75-.80 on a bicycle. This means we can roughly consider kilojoules of work produced to food Calories expended at a 1:1 ratio.
Lactate Threshold (LT)
Lactate threshold is the intensity at which there is a dramatic spike in blood lactate measured during an incremental exercise test. That point indicates when production exceeds our ability to clear lactate, and hence, our maximum sustainable effort. However, there are some complications to defining and describing what is happening at LT. This led to terms like LT1 (the point at which blood lactate level starts to rise above baseline) and LT2 (the point at which production exceeds clearance, sometimes called Onset of Blood Lactate Accumulation (OBLA)). Athletes sometimes use Lactate Threshold and Functional Threshold Power interchangeably, but they are not the same thing. See the FTP section above.
Normalized Power (NP)
Normalized Power is a weighted average power that emphasizes periods of higher power output and de-emphasizes lower power outputs and periods of coasting (zero power). NP aims to quantify the metabolic cost of a ride or segment of a ride. Normalized Power tends to be a better metric than just average power alone. This is because average power drops quickly with coasting and light effort. And at the other end of the spectrum, efforts significantly above FTP are dramatically fatiguing.
Normalized Power is important because it is used to calculate several other performance metrics. These include Intensity Factor, Efficiency Factor, Variability Index, and Training Stress Score (TSS). Training subsequently uses TSS to calculate Acute Training Load, Chronic Training Load, and Training Stress Balance.
Power-to-Weight Ratio (PWR)
Power-to-Weight Ratio is a cyclist’s power output divided by their weight in kilograms for a given duration or at a given intensity level. In other words, a cyclist who weighs 70 kilograms and produces 250 Watts for 30 minutes would have a PWR of 250 / 70 = 3.57 W/kg for 30 minutes. PWR increases for shorter efforts and decreases for longer efforts. As a result, our 70kg rider might have a PWR of 3.75 W/kg for 15 minutes and 3.0 W/kg for 60 minutes.
Fatigue affects PWR, too. Well rested, you might have a PWR of 3.57 W/kg for 30 minutes. However, at the end of a 4-hour ride or on Day 4 of a cycling tour, your best PWR for 30 minutes might diminish to 2.75 W/kg. Training goals can include increasing PWR ratio and increasing stamina or durability, so PWR declines less over the course of a long ride or multi-day event.
As described in this post, looking at power output relative to an individual’s weight can helps differentiate performance ability. Power-to-weight ratio can also be calculated to correspond to a given intensity level. Indoor cycling apps (Zwift, RGT, etc.) often categorize riders for virtual group rides and races through “power-to-weight ratio at FTP”.
You can increase PWR through weight loss and/or increasing power output. Focus first on improving fitness to increase power output. Some weight loss is likely to occur during the training process anyway. Proactive weight loss in pursuit of performance gains increases the risk of poor-quality workouts due to caloric restriction. And long-term, chronic energy deficiencies can result in Relative Energy Deficiency in Sport (RED-s).
Rating of Perceived Exertion (RPE)
Rating of Perceived Exertion, or RPE, is the simplest of all ways to gauge exercise intensity. It is simply a subjective measurement of how hard you feel you are going. Athletes and coaches typically use one of two RPE scales: the Borg Scale from 6-20 or a simpler 0-10 scale. In either scale, the harder your effort, the higher the RPE value.
With the Borg Scale, multiplying your stated value by 10 has been shown to provide a reasonable estimation of heart rate at the time. With the 0-10 scale, multiplying your stated value by 10 seems to correspond roughly with your current percentage of VO2 max. Neither is absolutely true for all athletes or in all circumstances. However, you’d be surprised how accurate they tend to be. You can also combine the scales with a “talk test” that gauges exercise intensity by how easily you can speak during exercise. There’s a chart of RPE and the Talk Test in this post.
RPE is perhaps the most important metric of all because it is the most accurate and effective gauge of exercise intensity during real-world exercise and competitions. An important goal we have when working with athletes is to teach them to train and race by feel. Often, an athlete’s best-ever performances happen when they tune into their bodies instead of watching the numbers. Keep recording the data to look at later, and so we have it for your long-term training history. But in the moment, you want to nail power, power, and heart rate values without looking at a display.
Training Stress Balance (TSB)
Training Stress Balance for today is the difference between yesterday’s Chronic Training Load and yesterday’s Acute Training Load, or TSB today = CTL yesterday – ATL yesterday. When the workload from yesterday’s ride was above your long-term average training load, TSB goes down. This indicates your readiness to train or perform today is lower than it was yesterday. Your “form” has declined. TSB goes down during periods of high training load, like during blocks of structured interval workouts or high-volume endurance rides. During effective training blocks athletes commonly see TSB values between -5 and -15. Sustained values below -20 indicate increased risk for overtraining.
Training Stress Balance goes up when you rest, or when yesterday’s workload was lower than your long-term average. As TSB goes up, your readiness to train or perform increases. TSB values between +5 and +15 often correspond with good to great performance outcomes. Sustained TSB values above +20 or +30 may indicate detraining.
For athletes with Strava memberships, the “Form” line on the “Fitness and Freshness” chart represents a calculation similar to TSB.
Training Stress Score (TSS)
Dr. Andy Coggan and Hunter Allen developed Training Stress Score to quantify the training load of individual workouts in a single metric that accounted for both intensity and duration. Cycling TSS allows athletes to compare the physiological stress created by a short, high intensity workout to the stress of a 3-hour endurance ride. TrainingPeaks calculates Acute Training Load and Chronic Training Load using Daily TSS (dTSS).
Although TSS is very valuable metric, cyclists can sometimes overestimate its importance. TSS doesn’t incorporate several aspects of training that should be considered when evaluating and prescribing workouts. For more, read this detailed post on TSS and how to use it.
Variability Index (VI)
Credited to Charles Howe and described in Training and Racing with a Power Meter, 3rd Ed., VI is the ratio of NP to AP, or NP/AP for a workout, race, or segment of data. A VI of 1.0 means NP=AP, which describes a perfectly steady effort. Highly variable rides have higher VI values. So, a flat time trial on an ergometer would be 1.0 or close to it. At the other end of the spectrum, criteriums or mountain bike races that feature repeated high-power efforts but also lots of coasting, could produce VI values of 1.15-1.50.
Power output is energy output over time, which is expressed in watts. It’s calculated using the following equation: Power = Force x Velocity. More specifically for cycling, power is the product of torque (force acting on an object to make it rotate) and cadence (pedal speed). Watts are part of nearly every term and calculation described in this post. Read more about power in “The Essential Guide to Training With a Power Meter”.
By Chris Carmichael,
Founder and Head Coach of CTS