Training Periodization: The Fitness-Fatigue Model

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Taper gain ≈ 3-5% — supercompensation achieved

A 2-week taper after consistent training at 200 AU/week produces a 3-5% performance improvement. Fitness (τ=42d) decays slowly while fatigue (τ=7d) drops rapidly, creating a readiness peak around day 10-14 of the taper.

Formula

Performance(t) = p₀ + k₁ × Σ w(i) × Math.exp(-(t-i)/τ₁) - k₂ × Σ w(i) × Math.exp(-(t-i)/τ₂)
Fitness(t) = Σ w(i) × Math.exp(-(t-i)/τ_fitness)
Fatigue(t) = Σ w(i) × Math.exp(-(t-i)/τ_fatigue)

The Science of Peaking on Race Day

Every serious athlete faces the same paradox: training makes you fitter but also more tired. The art of periodization is managing this trade-off so that peak fitness and minimal fatigue coincide on competition day. The Banister fitness-fatigue model provides the mathematical framework for understanding this balance and designing optimal training plans.

Two Competing Processes

Each training session produces two effects: a fitness gain and a fatigue penalty. Both decay exponentially over time, but at very different rates. Fitness has a long time constant (about 42 days), meaning it builds and fades slowly. Fatigue has a short time constant (about 7 days), meaning it accumulates and dissipates quickly. Performance at any moment is the difference between accumulated fitness and accumulated fatigue.

The Taper: Where Science Meets Strategy

A taper is a planned reduction in training load before competition. By reducing load to 40-60% of normal, fatigue drops rapidly while fitness barely changes. The result is a supercompensation peak — a window of 1-3 weeks where the athlete performs 2-5% better than during full training. This small percentage is enormous in elite sport, where margins of victory are fractions of a percent.

Practical Periodization

Modern periodization extends the fitness-fatigue model into structured training blocks: base building (high volume, moderate intensity), specific preparation (race-pace work), and the taper. This simulation lets you experiment with different load patterns and time constants to find the combination that produces the highest performance peak at exactly the right moment.

FAQ

What is the fitness-fatigue model in sports science?

The Banister impulse-response model describes performance as the difference between two exponentially decaying effects of training: fitness (positive, slow-decaying with τ ≈ 42 days) and fatigue (negative, fast-decaying with τ ≈ 7 days). Performance = fitness - fatigue, which explains why athletes feel worse during heavy training but better after tapering.

Why does tapering improve performance?

During a taper, training load is reduced by 40-60%. Because fatigue dissipates faster than fitness (7 vs 42 day time constants), the net effect is a rapid drop in fatigue while fitness remains nearly unchanged. This creates a supercompensation window where performance peaks 2-3% above pre-taper levels.

How long should an optimal taper be?

Research consistently shows that 2-3 week tapers with 40-60% load reduction produce optimal performance gains. Shorter tapers do not allow full fatigue dissipation; longer tapers risk fitness detraining. The optimal duration depends on the individual's fatigue and fitness time constants.

What are arbitrary units (AU) in training load?

Training load in arbitrary units quantifies the dose of training stress. Common methods include session RPE (rate of perceived exertion × duration in minutes), TRIMP (heart rate-based), or Training Stress Score (power-based in cycling). The absolute number matters less than relative changes and consistency.

Sources

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