You've spent time with Sequorr's analytics dashboard, you've seen three numbers that sit at the center of your training picture: TSS, CTL, and ATL. These aren't arbitrary — they're the foundation of how structured training actually works, and understanding them puts you in control of your fitness trajectory instead of guessing.
This guide breaks down what each metric means, how Sequorr algorithm works, and most importantly how you can use them to build into readinesss, manage fatigue, and peak at race day.
What Is Training Stress Score (TSS)?
TSS is a single number that captures how hard a workout was relative to what you're capable of. It accounts for both the duration and the intensity of your session — a short, explosive tempo run and a long easy effort can produce similar TSS values for very different reasons.
Think of it as a cost model. Every session you do has a dependant cost variable. The question is whether you're spending wisely relative to what you're trying to build.
Some practical anchors to help you calibrate:
- Easy 60-min run - ~40-50 TSS
- Threshold 60-min run - ~100 TSS
- Long run (2.5 hrs, moderate) - ~150-180 TSS
- Marathon race effort - ~250-350 TSS
CTL: Chronic Training Load (Your Fitness)
CTL is an exponentially-weighted rolling average of your daily TSS over roughly the last 42 days. It represents your accumulated training — what your body has absorbed and adapted to over weeks of consistent work.
The key property of CTL is that it rises slowly and falls slowly. You can't cram in a training session the same way you can squeeze in a coffee break. It takes consistent loading over weeks to move the needle. But the flip side is reassuring: a few missed days don't erase what you've built.
Reading your CTL trend
- Steady upward slope — You're building fitness. This is what a well-structured training block looks like.
- Plateau — You're maintaining. Fine for some phases, but if you've been here for weeks, it might be time to add load.
- Declining — You're losing fitness. Expected during a taper, concerning outside of one.
ATL: Acute Training Load (Your Fatigue)
ATL works identically to CTL but with a 7-day time constant. It represents your short-term training load — essentially, how fatigued you are from recent sessions.
ATL is your early warning system. When it's significantly higher than your CTL, your body is accumulating stress faster than it can absorb. That's fine for a few days however, sustained for too long- it's a recipe for overtraining, illness, or injury.
TSB: Training Stress Balance (Your Form)
This is where it all comes together. TSB is simply the difference between your fitness and your fatigue:
The training cycle, visualized
Here's how a smart training block flows through these numbers:
- Build phase — Heavy training. TSB drops negative (-10 to -30). You feel the legs churning. This is the heavy work.
- Recovery week — Reduced volume. ATL drops, TSB moves toward zero. You're pacing alongside the work.
- Repeat — Each cycle, your CTL is a little higher. You're progressing relative to your input.
- Taper — 10-14 days before the race, you reduce load sharply. ATL plummets. CTL dips only slightly (42-day window, remember). TSB rises into positive territory.
How Sequorr Calculates This For You
Sequorr's training engine runs these calculations automatically using your synced activity data. Breakdown of how the calculations work:
- TSS is computed per activity using heart rate zones mapped to your threshold, or pace-based estimates when HR data isn't available. No hardware lock-in — if your watch captures the data, Sequorr uses it.
- A nightly cron job recalculates your CTL, ATL, and TSB using exponentially-weighted averages with 42-day and 7-day time constants respectively.
- The Performance Management Chart (PMC) on your dashboard plots all three over time, so you can see at a glance where your training has been and where you're heading.
We don't charge for this. These analytics are core to Sequorr and will always be free.
Practical Guidelines for Endurance Athletes
Weekly TSS targets by phase
These are rough ranges for a runner training 5-6 days per week. Your numbers will depend on your threshold and total volume, but the ratios matter more than the absolutes:
- Base building — 300-450 TSS/week, mostly easy aerobic work
- Build phase — 450-600 TSS/week, more intensity mixed in
- Peak week — 500-700 TSS/week (your biggest training week)
- Taper — Drop to 40-60% of peak week TSS
The 5-7% rule
A commonly cited guideline is to increase CTL by no more than 5-7 points per week. Ramp faster and you risk injury; ramp slower and you might not be progressing fast enough for your goal pace. Sequorr's dashboard makes this easy to monitor — just watch your CTL trend line.
Recovery weeks
Every 3-4 weeks, drop your training load by 30-40%. This lets ATL fall, TSB recover, and your body actually absorb the training you've done. Skipping recovery weeks is the most common mistake self-coached athletes make.
The Bottom Line
TSS, CTL, ATL, and TSB aren't psuedo science — they're scientifically researched and mathematically backed. But they give you something powerful: a shared language for understanding training cycles that remove guesswork and replaces it with intentional signals.
You don't need a coach to use these numbers. You need consistency, patience, and a willingness to trust the process. Sequorr puts the data in your hands. What you build with it is up to you.