Training Peaks Fully Explained: TSS, ATL, CTL and Race Preparation Adjustments

Introduction

If a coach you know has ever mentioned “TSS,” “CTL,” or the “PMC chart,” they are speaking the language of Training Peaks. Training Peaks is currently the most widely used training management platform among professional endurance athletes and coaches worldwide. Its core framework was developed by exercise physiologists Andrew Coggan and Hunter Allen, based on the Banister Impulse-Response model. While this system has a learning curve, once understood, it will completely change how you plan your training.

TSS: Training Stress Score

TSS (Training Stress Score) is the core metric that quantifies the “overall stress” of a single workout, taking both intensity and duration into account. The calculation formula is as follows:

TSS = (Training seconds × Normalized Intensity × Intensity Factor) ÷ (Threshold Power or Threshold Pace × 3600) × 100

For running, TSS is calculated based on your lactate threshold pace (the pace corresponding to your LTHR). You don’t need to calculate it manually—Training Peaks calculates it automatically once you input your threshold.

A few practical reference values:

CTL, ATL, TSB: The Triangular Balance of Training

These three metrics are collectively known as the PMC three metrics (Performance Management Chart), and they are Training Peaks’ most core analytical tools:

CTL (Chronic Training Load): The exponentially weighted average of TSS over the past 42 days, reflecting your current aerobic fitness base—your “savings.” The higher your CTL, the stronger your aerobic foundation. For runners targeting a sub-4 full marathon, CTL during the preparation period should be around 50–65; for sub-3:30, around 65–80; and for sub-3, you need to reach 80–100 or above.

ATL (Acute Training Load): The weighted average of TSS over the past 7 days, reflecting short-term fatigue levels—your “debt.”

TSB (Training Stress Balance): TSB = CTL − ATL, reflecting your current physical state (Form).

How to Use the PMC Chart to Plan Marathon Preparation

Using the Taipei Marathon (held every December) as a target, here is a CTL progression strategy for a 20-week preparation structure:

Weeks 1–4 (Base Phase): CTL gradually climbs from 40 to 55, with TSB maintained in the -5 to -15 training zone
Weeks 5–12 (Build Phase): CTL continues to rise to 70–80, with a CTL plateau (recovery week) scheduled every 4 weeks
Weeks 13–16 (Intensification Phase): Add long tempo runs and threshold training; CTL stays at its peak but is no longer forced upward
Weeks 17–18 (Taper Phase 1): TSS drops to 70% of normal, CTL begins to slowly decline, and TSB gradually turns positive
Week 19 (Race Week): TSS drops to 40–50% of normal, with a TSB target of +10 to +20
Race Day: TSB target of +15 to +25, with CTL still maintained at its peak (not dropping significantly due to tapering)

Safe Range for CTL Increase Rate

This is the most important yet most overlooked detail in Training Peaks: weekly CTL increases should not exceed 5–8 points. If your current CTL is 50, it should not suddenly jump to 60 the following week. Excessively rapid CTL increases are typically accompanied by a higher risk of injury—iliotibial band syndrome and plantar fasciitis often occur this way.

Practical Recommendations

• Set the correct threshold first: All of Training Peaks’ calculations are based on your threshold pace or threshold heart rate. An incorrect threshold setting will render all numbers meaningless. It is recommended to use the average pace from a 30-minute all-out test × 1.05 as your threshold pace
• Review the PMC chart every Sunday: Confirm whether this week’s CTL increase is within the safe range and whether TSB aligns with the current training phase
• Reset your plan after a race: After a full marathon, TSB typically drops below -50. You need 3–4 weeks for TSB to return to positive before starting the next preparation cycle

Conclusion

TSS, CTL, and ATL are not esoteric sports science jargon—they are navigation tools that help you find the optimal path between “training enough” and “training into injury.” When the three lines on the PMC chart move according to your plan, your confidence on race day will be completely different.

Related Reading

• Triathlon Data Analysis: How to Use TrainingPeaks to Manage Three-Sport Training Load
• TSS, CTL, ATL: A Complete Breakdown of the Three Key Training Load Metrics
• TSS, CTL, ATL, TSB Complete Guide: The Calculation Principles and Applications of Training Stress Indexes
• Interpreting the PMC Fitness Management Chart: How the Three Numbers ATL, CTL, and TSB Guide Your Training Cycles