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Training Load Calculator

Monitor fitness, fatigue, and form with training load metrics

Today's TSS

42.2

ACWR

1.17

Zone

Sweet Spot

TSB

9.1

7-day smoothed training load (from your training platform)

42-day smoothed training load (from your training platform)

Workout Stress

42.2

Training Stress Score

TSS/Hour

56.3

IF

0.75

Fitness / Fatigue / Form

CTL (Fitness)49.6
ATL (Fatigue)40.5
TSB (Form)+9.1

Workload Ratio

1.17

Sweet Spot

0.00.81.32.0

Injury risk: Low

What You'll Need

Amazon Basics Rubber Hex Dumbbell Pair 20lb

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Fit Simplify Resistance Loop Exercise Bands Set of 5

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Rogue Fitness Ohio Cerakote Barbell 20kg

Rogue Fitness Ohio Cerakote Barbell 20kg

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Garmin Forerunner 165 GPS Running Smartwatch

Garmin Forerunner 165 GPS Running Smartwatch

$250-$3004.6
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Nathan QuickSqueeze 12oz Handheld Running Water Bottle

$14-$224.5
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Body Glide Original Anti-Chafe Balm 2.5oz

$9-$124.7
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Amazon Basics Rubber Hex Dumbbell Pair 20lb

$35-$504.7
View on Amazon

Fit Simplify Resistance Loop Exercise Bands Set of 5

$10-$154.5
View on Amazon
Rogue Fitness Ohio Cerakote Barbell 20kg

Rogue Fitness Ohio Cerakote Barbell 20kg

$280-$3504.8
View on Amazon
Garmin Forerunner 165 GPS Running Smartwatch

Garmin Forerunner 165 GPS Running Smartwatch

$250-$3004.6
View on Amazon

Nathan QuickSqueeze 12oz Handheld Running Water Bottle

$14-$224.5
View on Amazon

Body Glide Original Anti-Chafe Balm 2.5oz

$9-$124.7
View on Amazon

As an Amazon Associate, we earn from qualifying purchases.

Frequently Asked Questions

Q

What is training stress score (TSS) for running?

TSS quantifies the training load of a single workout based on duration and intensity relative to your threshold pace. A 60-minute run at threshold pace = 100 TSS. Easier runs score less, harder intervals score more per minute. Weekly TSS of 300-500 is typical for recreational runners.

  • TSS = (Duration × IF² × 100) / 3600, where IF = intensity factor
  • IF = workout pace as a fraction of threshold pace
  • Easy run (70% effort): ~40-60 TSS per hour
  • Tempo run (85-90%): ~80-100 TSS per hour
  • Intervals (95%+): ~100-130 TSS per hour
Workout TypeTypical IFTSS per HourRecovery Time
Easy run0.70-0.8050-65< 24 hours
Tempo run0.85-0.9080-10024-36 hours
Threshold run0.95-1.0090-10036-48 hours
VO2max intervals1.05-1.15110-13548-72 hours
Q

What is the acute-to-chronic workload ratio (ACWR)?

ACWR compares your recent training load (acute, last 7 days) to your long-term average (chronic, last 28 days). An ACWR of 0.8-1.3 is the "sweet spot" for adaptation without excessive injury risk. Above 1.5 signals danger. Below 0.8 means detraining.

  • ACWR = Acute Load (7-day) / Chronic Load (28-day)
  • Sweet spot: 0.8-1.3 for safe progression
  • Danger zone: above 1.5 (rapid ramp-up)
  • Detraining: below 0.8 (doing too little)
  • The 10% rule roughly corresponds to ACWR of ~1.1
ACWR RangeZoneInjury RiskRecommendation
< 0.8UndertrainingModerate (detraining)Gradually increase volume
0.8 - 1.0MaintenanceLowSafe to hold steady
1.0 - 1.3Sweet SpotLowOptimal for adaptation
1.3 - 1.5CautionModerateMonitor closely
> 1.5DangerHighReduce load immediately
Q

How do CTL, ATL, and TSB work together?

CTL (Chronic Training Load) = fitness. ATL (Acute Training Load) = fatigue. TSB (Training Stress Balance) = CTL minus ATL = form. Positive TSB means you are fresh (good for race day). Negative TSB means fatigued (normal during training blocks).

  • CTL uses 42-day exponentially weighted moving average
  • ATL uses 7-day exponentially weighted moving average
  • TSB = CTL - ATL (positive = fresh, negative = fatigued)
  • Race-day TSB target: +10 to +25 for best performance
  • Heavy training block: TSB of -10 to -30 is normal
MetricFormulaTime ConstantRepresents
CTL (Fitness)EWMA of TSS42 daysLong-term training load
ATL (Fatigue)EWMA of TSS7 daysShort-term training load
TSB (Form)CTL - ATLN/AReadiness to perform
Q

What weekly TSS should I target?

Recreational runners: 200-400 TSS/week. Competitive amateur: 400-600. Elite: 600-1000+. Build no more than 10-15% per week. A single hard week above 150% of normal load significantly increases injury risk in the following 2 weeks.

  • Beginner: 150-250 TSS/week (3-4 easy runs)
  • Recreational: 300-400 TSS/week (4-5 runs with one workout)
  • Competitive: 450-650 TSS/week (6 runs, 2 quality sessions)
  • Elite: 700-1000+ TSS/week (doubles, high mileage)
  • Recovery week: reduce to 60-70% of normal TSS
LevelWeekly TSSWeekly MilesQuality Sessions
Beginner150-25015-250-1
Recreational300-40025-401
Competitive450-65040-602
Elite700-1000+70-1202-3
Q

How is the exponentially weighted moving average calculated?

EWMA gives recent days more weight than older days. For ATL: decay = 2/(7+1) = 0.25. For CTL: decay = 2/(42+1) ≈ 0.047. Each day: new average = previous average × (1 - decay) + today's TSS × decay. This smooths daily variation while responding to trends.

  • Decay factor (alpha) = 2 / (N + 1) where N = time constant in days
  • ATL alpha = 2/8 = 0.25 (responds quickly to recent training)
  • CTL alpha = 2/43 = 0.0465 (responds slowly, captures fitness)
  • Day 1 value can be seeded with first workout TSS or 0
  • After ~3x the time constant, initial seed value has minimal effect

Example Calculations

1Easy Run (45 min at 65% effort)

Inputs

Duration45 minutes
Intensity Factor0.75
Threshold Pace4:30/km

Result

Training Stress Score42.2 TSS
TSS per Hour56.3
Estimated Pace6:00/km

TSS = (45 × 60 × 0.75² × 100) / 3600 = (2700 × 0.5625 × 100) / 3600 = 151875 / 3600 = 42.2 TSS.

2Tempo Run (30 min at threshold)

Inputs

Duration30 minutes
Intensity Factor1.00
Threshold Pace4:30/km

Result

Training Stress Score50.0 TSS
TSS per Hour100.0
Estimated Pace4:30/km

TSS = (30 × 60 × 1.00² × 100) / 3600 = (1800 × 1.0 × 100) / 3600 = 180000 / 3600 = 50.0 TSS. At IF = 1.0, TSS per hour = 100, so 30 min = 50 TSS.

3Weekly Load Assessment

Inputs

This Week TSS350
Last 4 Weeks Avg TSS300

Result

ACWR1.17
ZoneSweet Spot
Injury RiskLow

ACWR = Acute (350) / Chronic (300) = 1.17. This is within the 0.8-1.3 sweet spot, indicating safe progression with low injury risk.

Formulas Used

Training Stress Score

TSS = (Duration (sec) × IF² × 100) / 3600

Quantifies the training load of a single workout.

Where:

Duration= Workout duration in seconds
IF= Intensity Factor = ratio of workout pace to threshold pace (1.0 = threshold)
100= Normalizing constant (1 hour at threshold = 100 TSS)

Exponentially Weighted Moving Average

EWMA(today) = EWMA(yesterday) × (1 - α) + TSS(today) × α

Smoothed average that weights recent data more heavily. Used for both ATL and CTL.

Where:

α (alpha)= Decay factor: 2/(N+1) where N = time constant (7 for ATL, 42 for CTL)
EWMA(yesterday)= Previous day smoothed average
TSS(today)= Training stress score for today (0 on rest days)

Acute-to-Chronic Workload Ratio

ACWR = Weekly TSS / Average Weekly TSS (4 weeks)

Ratio of recent load to long-term load. Sweet spot is 0.8-1.3.

Where:

Weekly TSS= Current week total Training Stress Score
Average Weekly TSS (4 weeks)= Average of the last 4 weeks total TSS

Understanding Training Load and Stress Balance

1

TSS: Quantifying Individual Workout Stress

100 TSS equals exactly 1 hour at lactate threshold pace (Intensity Factor = 1.0). This anchor point makes TSS intuitive: a 45-minute easy run at IF 0.75 produces 42 TSS, while a 30-minute VO2max interval session at IF 1.10 produces 60.5 TSS. Despite being 15 minutes shorter, the interval session generates 44% more training stress because intensity is squared in the formula (TSS = duration × IF² × 100 / 3600).

The Intensity Factor (IF) is the ratio of your workout pace to your threshold pace. An easy run at 6:00/km for a runner with a 4:30/km threshold has IF = (4.5/6.0) = 0.75. A tempo run at 5:00/km has IF = (4.5/5.0) = 0.90. Interval sessions where some portions exceed threshold can produce IF values above 1.0 because the squaring of IF amplifies the contribution of high-intensity segments.

For runners without power meters, pace-based IF estimation works well on flat terrain. On hilly routes, heart rate-based IF is more accurate because uphill running at threshold heart rate may show a much slower pace. The tempo run pace calculator can derive your threshold pace from a recent race, giving you the anchor for all IF calculations.

All calculations assume threshold pace IF = 1.00
WorkoutDurationIFTSSRecovery Needed
Easy run60 min0.7556< 24 hours
Long run120 min0.7812236–48 hours
Tempo run45 min0.906124–36 hours
Threshold intervals35 min1.005836–48 hours
VO2max intervals25 min1.125248–72 hours
2

CTL, ATL, and TSB: The Fitness-Fatigue Model

CTL (Chronic Training Load) uses a 42-day exponentially weighted moving average (EWMA) of daily TSS. It responds slowly to changes, rising during consistent training blocks and declining during rest. A recreational runner averaging 45 TSS per day (315/week) has a CTL of approximately 45. Building CTL by more than 5–7 points per week risks overtraining.

ATL (Acute Training Load) uses a 7-day EWMA and responds rapidly to recent training. A heavy training week of 500 TSS immediately spikes ATL, even if the prior month averaged 300/week. ATL serves as a fatigue indicator: when ATL is significantly higher than CTL, the runner is accumulating fatigue faster than fitness – a recipe for injury if sustained.

TSB (Training Stress Balance) = CTL − ATL. When TSB is positive (+5 to +25), the runner is fresh and ready to race. When negative (−10 to −30), the runner is in a productive overreach state typical of build weeks. For race-day performance, taper training to achieve TSB between +10 and +25 by reducing volume 40–60% over 10–14 days while maintaining some intensity.

Fitness – Fatigue = FormCTLFitness (42d)−ATLFatigue (7d)=TSBFormBuilds over weeksResponds in daysPositive = FreshNegative = TiredRace-day TSB target: +10 to +25
3

Acute-to-Chronic Workload Ratio and Injury Prevention

The ACWR divides your 7-day load by your 28-day average load. An ACWR of 1.0 means you are training at your chronic baseline. An ACWR of 1.2 means you are training 20% above your chronic baseline – within the 0.8–1.3 sweet spot identified by Tim Gabbett’s research in the British Journal of Sports Medicine (2016).

Injury risk spikes when ACWR exceeds 1.5. A runner averaging 300 TSS/week who suddenly ramps to 450 TSS (ACWR = 1.5) faces 3–5× the baseline injury risk in the following 7–14 days. The most common scenario: returning from a 2-week taper or injury layoff and attempting to resume pre-break volume immediately. The chronic load has dropped during rest, so even "normal" training volume produces a dangerously high ACWR.

Monitoring ACWR is particularly important during marathon training cycles, where weekly mileage can swing 20–40% between build and recovery weeks. A well-structured plan keeps ACWR between 0.9 and 1.25 during build phases, drops to 0.7–0.8 during recovery weeks, and never exceeds 1.3 for more than one consecutive week. Use the marathon pace calculator to plan race-specific workouts that fit within safe ACWR ranges.

Based on Gabbett BJSM 2016 injury risk thresholds
ACWRClassificationWeekly TSS (chronic 350)Action
0.6–0.8Undertraining210–280Ramp up gradually
0.8–1.0Maintenance280–350Safe to hold
1.0–1.3Sweet Spot350–455Optimal for gains
1.3–1.5Caution455–525Limit to 1 week max
> 1.5Danger> 525Reduce immediately

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Last Updated: Mar 25, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.

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