Training Stress Score Calculator

Training Stress Score (TSS) is a metric developed by Dr. Andrew Coggan that quantifies the training load of a workout. It combines workout duration and intensity relative to your threshold (FTP for cycling, threshold pace for running). A TSS of 100 equals one hour at threshold intensity. TSS allows you to compare workouts of different durations and intensities on a common scale.

Cycling TSS is calculated using the formula: TSS = (Duration in seconds x Normalized Power x Intensity Factor) / (FTP x 3600) x 100. In simplified form: TSS = Duration (hours) x IF² x 100. You need a power meter and your FTP to calculate accurate TSS. The Intensity Factor (IF) is your Normalized Power divided by FTP.

Running TSS (rTSS) is a pace-based training stress metric for runners. It uses your threshold pace (pace you can sustain for about 60 minutes) and actual workout pace to calculate training load. The formula accounts for the exponential relationship between pace and effort, recognizing that small pace increases require disproportionately more effort.

Heart Rate TSS (hrTSS) calculates training stress using heart rate data when power or pace data isn't available. It uses your lactate threshold heart rate (LTHR) as the reference point. While less accurate than power-based TSS due to cardiac drift and other factors, hrTSS is useful for activities where power measurement isn't practical, like hiking, swimming, or strength training.

CTL (Chronic Training Load) represents your fitness level as a 42-day exponentially weighted average of daily TSS. It reflects the long-term training load your body has adapted to. Higher CTL indicates greater fitness capacity. Building CTL takes time and consistency - expect about 1 point increase for every ~100 TSS accumulated, with diminishing contributions from older workouts.

ATL (Acute Training Load) represents your fatigue level as a 7-day exponentially weighted average of daily TSS. It reflects recent training stress that hasn't been fully absorbed. High ATL indicates accumulated fatigue from recent training. ATL responds quickly to changes in training load, rising fast during hard training blocks and dropping quickly during rest periods.

TSB (Training Stress Balance) is calculated as CTL minus ATL and represents your form or freshness. Positive TSB indicates you're rested and ready to perform. Negative TSB indicates accumulated fatigue. Optimal race TSB is typically +15 to +25. During heavy training, TSB will be negative (-10 to -30), which is necessary for adaptation but not ideal for peak performance.

Weekly TSS targets vary by athlete level and goals: Recreational (200-400), Competitive Amateur (400-600), Serious Amateur (600-800), Elite/Pro (800-1200+). The key is progressive overload - increase weekly TSS by no more than 5-10% to avoid overtraining. Every 3-4 weeks, include a recovery week at 60-70% of normal load.

Warning signs include: TSB below -30 for extended periods, weekly TSS increases greater than 15%, persistent fatigue despite rest days, declining performance with increased training. Single workouts over TSS 300-400 require significant recovery time. If you notice elevated resting heart rate, decreased HRV, or mood disturbances alongside high TSS, reduce training immediately.

Plan weekly TSS distribution with 2-3 hard days (TSS 100-150+) and recovery days (TSS 30-50). Build CTL gradually during base phase, maintain during competition phase, and reduce TSS 40-60% during taper. Monitor TSB to peak for key events - start tapering 7-14 days before an A-race to achieve TSB of +15 to +25 on race day.

Intensity Factor (IF) is the ratio of workout intensity to threshold. For cycling, IF = Normalized Power / FTP. For running, IF = Threshold Pace / Workout Pace. An IF of 1.0 means threshold intensity. IF below 0.75 is endurance/recovery, 0.75-0.85 is tempo, 0.85-0.95 is threshold, 0.95-1.05 is sweet spot, and above 1.05 is VO2max/anaerobic intensity.

Recovery time depends on TSS magnitude: Low (under 150) - typically recoverable by next day, Medium (150-300) - requires 1-2 days of easy training, High (300-450) - needs 2-4 days of recovery, Very High (450+) - may need 4-7+ days. Individual recovery capacity varies based on fitness, age, sleep, nutrition, and overall stress levels.