We’re all chasing peak fitness. We want it on — not before, not after — the day of our highest priority race. Timing that kind of fitness is a top concern for athletes. That concern can quickly morph into a struggle without a solid understanding of a few cycling terms: TSS, ATL, CTL and TSB.

Author’s note: Many terms used within this blog post including Training Stress Score (TSS), Intensity Factor (IF), Normalized Power (NP), Acute Training Load (ATL), Chronic Training Load (CTL), Training Stress Balance (TSB) and Functional Threshold Power (FTP) are registered trademark terms owned by TrainingPeaks.

TSS (Training Stress Score) AKA A Measure of Your Hard Work

The intensity factor (IF) and duration of a workout determines TSS. IF can be defined a few ways. It can be based off of your Functional Threshold Power (this is the ideal), heart rate or Rate of Perceived Exertion (RPE). Having numerical values that represent the intensity and duration of your workout are the first steps in calculating TSS. Once you have those, you can pop them into this formula from TrainingPeaks:

TSS = (# of seconds of the workout x Normalized Power x Intensity Factor) / (FTP x 3600) x 100

If you’re wondering what that “3600” represents, it’s the number of seconds in the hour; and that “100” is there because FTP equals 100 TSS for one hour.

Why TSS matters?

Knowing how hard you worked, i.e. your training load or physical stress, during a workout allows you to estimate the potential fitness you’ll gain from your training session given adequate recovery. But that’s not all knowing your TSS is good for. Looking at your TSS can teach you when a workout is too much, when the weekly ramp rate is too high or when the weekly volume is too high to escalate week after week.

It’s important to note that high TSS does not guarantee an increase in fitness — intensity, duration or a combination of the two does. The TSS from two easy hours at 70% FTP, an hour-long workout at 99% FTP and 48 minutes of 150% FTP microbursts are all roughly the same: really close to 100. These three types of workouts all take very different tolls on the body and spur different physiological adaptations. So while total weekly stress is meaningful to know, IF is necessary for context. This is how a rider can go from something like a Traditional Base training plan with a 500-600 TSS/week and drop into a Build plan and then a Specialty plan (both with potentially less weekly TSS) and their fitness can still be rising.

One final note on TSS: Knowing it also plays into gauging the need for more or less recovery. Any time recovery is hampered or performance isn’t in line with expectations, reviewing TSS can help home in on the tipping point.

ATL (Acute Training Load) AKA a Measure of Your Fatigue

Your current level of fatigue is measured by ATL. This is based off a combination of frequency, duration and intensity of the workouts you performed in the last week of your training.

Why ATL matters?

Identifying levels of fatigue helps you forecast how much recovery you may or may not need in the future. As you add up days of high-TSS workouts and in turn ramp your weekly TSS, your fatigue will rapidly increase and your body will soon start to feel the effects of your training.

CTL (Chronic Training Load) AKA a Measure of Your Fitness

Different from ATL, CTL takes into account the consistency, duration and intensity of the last 6 weeks to several months or more of your training. This determines your current level of fitness — or just “fitness.”

Why CTL matters?

Properly progressed training over a long period of time commonly raises a rider’s CTL. This is what we all want. Ideally, week after week your CTL will ramp up, allowing for positive adaptations when done at the proper rate. You’ll likely notice that as your CTL (fitness) goes up, that amount of ATL (fatigue) you’re able to handle does too.

It’s important to note increasing CTL doesn’t automatically assume athletes need to be shooting for high TSS. Increasing simply means increasing your TSS over time with your body’s rate of adaption. Low-volume athletes can still build good fitness on 3 days/week and relatively low TSS.

TSB (Training Stress Balance) AKA a Measure of Your Form

TSB is the balance between CTL and ATL commonly referred to as form. So, TSB = CTL – ATL. Form comes about when your fitness (CTL) is high and your freshness (TSB) is positive.

A higher ATL than CTL results in a negative TSB (not fresh) and lower ATL than CTL results in a positive TSB (fresh). Just how positive your TSB needs to be to race well varies. Some athletes race well with a slightly positive TSB, e.g. +10, while others need it to be highly positive, e.g. +30. This often boils down to things like an athlete’s age, training experience, the type of event and the volume of training.

Why TSB matters?

Your TSB should be on the positive side of things if your goal is to go into a race at peak fitness. This essentially means your CTL (fitness) is high and your ATL (fatigue) is low. If your TSB is not positive going into an event, this is a sign your fatigue level is still too high and that you should have tapered differently — longer or more substantially. The rule here is to avoid a high ATL relative to your CTL prior to an A-priority race.

In layman’s terms this simply means it’s not smart to do a big week of training prior to a big event. Your taper should always correspond with an increasing TSB. So, your ATL decrease should be enough to bring about a positive TSB without reducing your CTL so much that you lose noticeable fitness. When you taper, you actually see your CTL fall (i.e. fitness declines) but because your TSB/freshness rises, the decline in fitness is ideally outmatched by the increase in freshness — it’s a tightrope — because fitness is never static. This also explains why it would be so hard to maintain peak fitness for very long.

Keep in mind the the body absorbs training adaptations on about a 6-week delay (different types of fitness, different timelines, but fitness in general takes about 6 weeks to “stick”) so anything done inside of this window may not manifest on race day and only serve to delay freshness. This is why the default timeframe for CTL is 42 days.

The Big Picture

Once again, peak fitness is what we’re all after. The only way for us to achieve such form is through the proper balance of fitness and freshness. All these concepts may seem simple enough — and for the most part they are — but they are all dependent upon one very important thing: the ability to measure training stress.

Without an objective way to measure your training load, true properly structured training is not possible. Cyclists have to measure their training stress if they want to estimate, and thereby plan when they reach peak fitness. The most precise and widely accepted way of measuring training load is through training with power.

Quantifying your training is the first step in achieving more effective cycling training and a greater understanding how all your hard work on the bike influences your body. For many riders, this is a time for a lot of trial and error. For other riders who are following a discipline-specific structured training plan, this is a time for growth and fine-tuning what they’ve got.

© 2016. TrainerRoad, LLC. NP, IF and TSS are trademarks of Peaksware, LLC and are used with permission. Learn more at www.trainingpeaks.com

Listen to Experts Discuss TSS, ATL, CTL, TSB and More on the Ask a Cycling Coach Podcast

The meanings of these cycling terms were covered in episode 49 of the Ask a Cycling Coach podcast. Listen to the episode’s full recording below to hear this topic and others discussed by our certified cycling coaches.

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Additional Notes

TrainerRoad’s Ask a Cycling Coach podcast is dedicated to making you a faster cyclist. It gives you the chance to get answers to your cycling and triathlon training questions from USAC certified coaches Chad Timmerman, Jonathan Lee and special guests. Learn more about other topics we covered in the latest episode with our resources below:

  • How to figure out your power zones
  • How to figure out your heart rate zones
  • Are your heart rate zones accurate?
  • How to get started with structured training
  • How do you know if you have enough base fitness?
  • How to train for cyclocross
  • Best training plan for cyclocross
  • Should you train for running if you’re racing cyclocross?
  • What is CTL?
  • What is TSB?
  • How to measure your training load, fitness and fatigue
  • How to taper for a century
  • How to train for a gran fondo
  • Why triathletes need VO2 max training
  • How to use high intensity training for triathletes
  • How to use ramp tests to understand your performance
  • How to perform a ramp test
  • How to power the KICKR remotely
  • Is pedal smoothness important?
  • Why pedal drills matter
  • How to know if you have a bad pedal stroke
  • How to train for time trials
  • Low volume training plans: how to use them in race season
  • How to time your cyclocross training for a long season
  • How does fasted training work?
  • Is it important to eat before an indoor workout?
  • How to know if you’re a sprinter
  • How many watts is a good sprint?
  • Sprint race strategy
  • What to do in order to be a better sprinter
  • How to win races if you’re not a good sprinter

For more answers to your cycling training questions, listen to our podcast Ask a Cycling Coach — the only podcast dedicated to making you a faster cyclist. New episodes are released weekly.

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Jonathan Lee

Jonathan Lee is a Level II USA certified cycling coach and the host of the Ask a Cycling Coach podcast. His background in the sport of motocross has translated into a passion for cycling, mountain biking and all things training. If you have a training question, submit your question for Jonathan to answer on the next episode of TrainerRoad’s podcast.