Running TSS calculator

Training adaptation is driven by the balance between stress and recovery. Too little stress produces no improvement; too much stress without adequate recovery leads to overtraining, injury, and illness. Training load tracking gives you an objective way to monitor this balance over time.

TSS provides a single number that captures both how long and how hard a session was. This makes it possible to compare fundamentally different workouts — a 90-minute easy run versus a 45-minute threshold session — on the same scale. Without load tracking, runners tend to rely on feel alone, which is subjective, mood-dependent, and prone to systematic errors.

Consistent load monitoring helps identify patterns: whether weekly totals are trending upward too aggressively, whether recovery weeks are providing enough relief, and whether race-week tapers are reducing load appropriately.

One of the most important but widely misunderstood aspects of TSS is that equal scores do not mean equal fatigue. Consider two workouts that both produce a TSS of 100:

Workout A: 2.5 hours of easy running at IF 0.63. This session is primarily aerobic and produces mainly peripheral fatigue — tired legs but manageable stress on the nervous system.

Workout B: 1 hour of threshold intervals at IF 1.0. This session stresses the neuromuscular and metabolic systems heavily, despite the shorter duration and identical TSS.

The recovery demands are different: Workout B typically requires 24-48 hours more recovery than Workout A, even though TSS is identical. This is because TSS compresses intensity and duration into one number and loses information about the type of stress applied.

In practice, use TSS for weekly load trends and periodization decisions, but always consider the intensity distribution — how much time was spent above threshold — when planning recovery between sessions.

These three metrics extend TSS from individual sessions to training trends over weeks and months:

CTL (Chronic Training Load / Fitness): A 42-day rolling average of daily TSS. It represents your accumulated fitness — the training load your body has adapted to over roughly 6 weeks. Higher CTL generally means higher fitness, but it rises slowly and requires consistent training to build.

ATL (Acute Training Load / Fatigue): A 7-day rolling average of daily TSS. It represents recent fatigue — how much stress you have absorbed in the past week. ATL rises and falls quickly with training load changes.

TSB (Training Stress Balance / Form): CTL minus ATL. When TSB is positive, you are relatively fresh (fitness exceeds recent fatigue). When TSB is negative, you are carrying accumulated fatigue. The optimal TSB for racing is slightly positive (+5 to +15), which means you have reduced recent training enough to shed fatigue while maintaining fitness.

Most successful race tapers bring TSB from negative (training phase) to slightly positive (race readiness) over 1-3 weeks by reducing volume while maintaining occasional intensity touches.

Weekly TSS targets provide structure without prescribing exact workouts. General benchmarks for running:

Beginner (150-300 weekly TSS): Focus on consistency. Most sessions should be easy (TSS 30-50 each). One moderate session per week (TSS 70-100). Total weekly TSS grows gradually with mileage.

Intermediate (300-500 weekly TSS): Include 1-2 quality sessions per week (tempo, threshold). Easy days should genuinely be easy. Build weekly TSS by 5-10% across training blocks with recovery weeks every 3-4 weeks.

Advanced (500-800+ weekly TSS): Structured periodization becomes critical. Balance high-TSS long runs with high-intensity but moderate-TSS interval sessions. Use recovery weeks to drop TSS by 30-40% and allow adaptation. Monitor TSB trends to avoid sustained deep negative values.

A practical weekly pattern: 2-3 easy runs (TSS 30-50 each), 1 long run (TSS 80-150), 1-2 quality sessions (TSS 60-120 each), 1-2 rest or cross-training days (TSS 0-20). Adjust based on your fitness level and training phase.

Training Stress Score is a workload proxy built from intensity factor and duration. It is best used as a trend indicator over weeks rather than a single-session verdict (TrainingPeaks).

TSS does not capture biomechanics, heat strain, or terrain variations. That is why rTSS and hrTSS can diverge even on the same run.

IF expresses how hard a session is relative to your threshold anchor. Power uses normalized power vs FTP, pace uses threshold pace, and heart rate uses heart-rate reserve (TrainingPeaks IF guide).

hrTSS often runs higher on hot days or long hills because heart rate captures internal strain, while rTSS reflects external output. Use both to understand why a run felt harder than pace alone indicates (TrainingPeaks rTSS).

Use TSS to compare session stress and monitor weekly load trends. Pair higher-stress days with easy sessions, and plan recovery blocks when total TSS climbs quickly.

Avoid plugging in outdated threshold anchors. If your threshold changes, IF and TSS will drift. Also remember that TSS is an estimate, not a medical diagnosis.

For heart-rate methods, resting HR should be measured on waking and threshold HR should represent a sustainable hard effort (Karvonen).

TSS, IF, and NP are terms associated with TrainingPeaks. This calculator is an independent estimation tool and is not affiliated with TrainingPeaks.