Training Stress Score (TSS) is the number that turns every ride — long or short, easy or brutal — into a single measure of training load you can actually plan with. In this guide, you’ll learn how TSS is calculated, how it feeds the fitness, fatigue, and form numbers on your Performance Management Chart, and how to use a weekly TSS target to build fitness without digging yourself into a hole.
What Is Training Stress Score?
TSS, developed by Dr. Andrew Coggan, estimates the physiological stress of a workout by combining how long you rode with how hard you rode relative to your own threshold. One hour ridden exactly at your FTP (functional threshold power) scores 100 TSS — that is the anchor point the whole system hangs on.
Because it is indexed to your threshold, TSS is personal. A 300 TSS week for a new rider and a 300 TSS week for a Cat 2 racer represent a similar relative stress, even though the absolute power numbers are worlds apart.
Some reference points for a single ride:
- Under 150 TSS — low stress; most riders recover by the next day.
- 150–300 TSS — medium; some residual fatigue into the following day.
- 300–450 TSS — high; expect leftover fatigue for two days or more.
- 450+ TSS — very high; typically only long, hard days such as a big gran fondo.
How TSS Is Calculated
The formula is: TSS = (seconds × NP × IF) ÷ (FTP × 3600) × 100, where NP is Normalized Power (a weighted average that reflects how surgy the ride was) and IF is Intensity Factor (NP divided by FTP).
You never need to compute it by hand — every major head unit and platform (Garmin, Wahoo, TrainingPeaks, TrainerRoad, intervals.icu) does it automatically — but two worked examples make the logic click:
- A 1-hour ride at IF 0.85 (a classic sweet spot session) scores roughly 72 TSS.
- A 3-hour endurance ride at IF 0.65 scores roughly 127 TSS — longer, but each hour is far less stressful.
Notice that intensity is squared in effect: riding 10% harder adds much more stress than riding 10% longer. That is why a 90-minute race can leave you flatter than a 4-hour cafe ride. No power meter? Most platforms estimate hrTSS from heart rate — less precise, especially for short surgy efforts, but consistent enough to trend with.
Accurate TSS depends on an accurate FTP. If your threshold setting is months out of date, every number downstream is wrong — see our guide to Coggan power zones for how FTP anchors the whole zone system.
CTL, ATL, and TSB: Fitness, Fatigue, and Form
Daily TSS values feed three rolling averages that together form the Performance Management Chart (PMC). Understanding these three numbers is where TSS stops being trivia and starts steering decisions.
CTL — Chronic Training Load (“Fitness”)
CTL is a weighted average of your daily TSS over roughly the past 42 days. It rises slowly as you train consistently and falls slowly when you rest. Think of it as the size of your aerobic engine’s foundation: a rider holding a CTL of 70 is doing about 490 TSS per week, sustainably.
ATL — Acute Training Load (“Fatigue”)
ATL is the same calculation over roughly the past 7 days. It reacts fast — one big weekend spikes it. ATL is the short-term cost you pay for the long-term CTL gain.
TSB — Training Stress Balance (“Form”)
TSB is yesterday’s CTL minus yesterday’s ATL. Negative TSB means you are carrying more fatigue than fitness — normal and productive during a training block. Positive TSB means you are fresh. Race-day form typically lives between +5 and +25: fresh enough to perform, not so rested that you have gone stale. Getting there on the right date is the whole art of tapering for a race.
How Much Weekly TSS Should You Aim For?
There is no universal number — the right weekly TSS is whatever your current CTL says you are adapted to, plus a modest overload. Typical sustainable ranges look like this:
- Time-crunched riders (5–7 hrs/week): 250–400 TSS
- Committed amateurs (8–12 hrs/week): 400–700 TSS
- Racers (12–18 hrs/week): 700–1,000 TSS
- Pros: 1,000–1,500+ TSS
The safer guide is the ramp rate: aim to raise CTL by about 3–5 points per week during a build. Chasing more than 7–8 points per week for several weeks is the classic recipe for illness, staleness, or injury. Build for two to three weeks, then cut volume 40–50% for a recovery week and let TSB climb back toward zero — the structure at the heart of periodization.
Using TSS to Plan a Training Week
Here is a practical way to put the numbers to work. Suppose your target is 450 TSS this week:
- Anchor the key sessions first. Two quality days — say a 75 TSS sweet spot session and a 70 TSS interval day — claim 145 TSS.
- Add the long ride. A 2.5-hour endurance ride at IF 0.65 adds about 105 TSS. Running total: 250.
- Fill with easy volume. Two or three genuinely easy rides (40–70 TSS each) bring you to target without adding meaningful fatigue.
- Check the spacing. Keep hard days separated by at least one easy or rest day so ATL never runs away from you mid-week.
After each week, glance at the PMC: CTL should tick upward, and TSB should dip during loading weeks and recover during rest weeks. If TSB is buried below −25 for days on end and your legs feel like concrete, believe the chart.
The Limitations of TSS
TSS is a model, and every model leaves things out. Keep these caveats in mind before treating the number as gospel:
- Not all TSS is equal. 100 TSS of VO2 max intervals and 100 TSS of endurance riding create identical scores but very different recovery demands and adaptations.
- It only counts the bike. Poor sleep, work stress, heat, and altitude all raise the true cost of a ride without changing its score.
- It says nothing about durability. Two riders with equal CTL can differ hugely in how well they resist fatigue late in long events — which is why durability training deserves separate attention.
- Garbage in, garbage out. A stale FTP or a mix of power-based and heart-rate-based scores muddies every trend line.
Used with those caveats, TSS remains the best simple currency we have for training load — just let perceived effort, sleep, and motivation cast votes too.
Getting Started With TSS: A Checklist
- Test or estimate your FTP, and re-test every 6–8 weeks so the anchor stays honest.
- Pick one platform (TrainingPeaks, intervals.icu, TrainerRoad, Strava + plugins) and let every ride land there.
- Ride normally for 4–6 weeks to establish a baseline CTL before judging any of the numbers.
- Build with a ramp rate of 3–5 CTL points per week, inserting a recovery week every third or fourth week.
- Before your goal event, taper so TSB rises into the +5 to +25 window on race day.
Do that consistently for a season and the Performance Management Chart stops being an intimidating graph and becomes what it was always meant to be: a map of exactly how fit, how tired, and how ready you are.
TSS vs Other Load Metrics
TSS is not the only way to count training load, and knowing how the alternatives compare helps you read whatever your platform shows you.
- Kilojoules (kJ) measure total mechanical work. Great for fueling decisions — roughly 1 kJ equals 1 kcal for a cyclist — but blind to intensity: a slow century can out-score a savage criterium.
- sRPE (session RPE) multiplies ride minutes by a 1–10 effort rating. Crude but surprisingly robust, and it needs no sensors at all — a useful cross-check when your power data looks off.
- TRIMP and Strava’s Relative Effort are heart-rate-based cousins. They handle steady riding well but under-count short anaerobic surges, which barely move heart rate yet cost plenty.
- Platform-specific scores (Garmin’s Training Load, Xert’s XSS) follow the same philosophy with different math — pick one system and stay inside it rather than comparing numbers across platforms.
The common thread: every useful load metric multiplies some version of “how long” by “how hard.” TSS simply does it with the most transparent, threshold-anchored math — which is why it became the de facto standard.
Common TSS Questions
What is a good TSS for a one-hour ride?
By definition the ceiling is about 100 — that is a maximal hour at FTP. A hard one-hour interval session usually lands between 70 and 90, a steady tempo hour around 60–70, and a genuinely easy spin 30–45. If your “recovery rides” keep scoring 60+, they are not recovery rides.
Do commutes and casual rides count?
Yes — stress is stress, whether or not it felt like training. Record everything. Un-recorded riding shows up anyway, as fatigue your chart cannot explain.
Should TSS hit zero in a recovery week?
No. Cutting load to nothing makes CTL fall faster than necessary and often leaves you feeling worse, not better. Reducing weekly TSS by 40–50% is usually enough to shed fatigue while keeping the engine warm.
Why did a Zwift race feel harder than its TSS suggests?
Short, violently variable efforts push your anaerobic system far beyond what a threshold-anchored model captures, even with Normalized Power smoothing the spikes. Trust your body’s verdict on those days and pad in extra recovery.
