The Banister Model: Your Hidden Fitness Score
Why you can be the fittest you've ever been — and feel terrible.
You've had this experience. Maybe it was week six of a training push. You were hitting the gym five or six times a week, the loads were climbing, and your conditioning felt sharper than ever. Then one morning everything was heavy. The barbell felt like it gained 20 pounds overnight. The metcon that should have been manageable crushed you.
You weren't sick. You weren't injured. You were overtrained.
But here's the part that doesn't make sense: you were also fitter than you'd ever been. The fitness was real. It was hiding underneath the fatigue — buried so deep you couldn't access it.
This paradox is exactly what the Banister Impulse-Response Model explains. And it's the core of how WodPilot manages your training load.
Two Curves, One Body
In 1975, Dr. Eric Banister proposed that fitness and fatigue are two separate physiological responses to training. Every workout creates both:
- Fitness accumulates slowly and decays slowly — with a time constant of
45 days(tau_fitness). A hard workout you did a month ago is still contributing to your fitness today. - Fatigue accumulates quickly and decays quickly — with a time constant of
15 days(tau_fatigue). Yesterday's hard workout creates a lot of fatigue, but last month's has almost none left.
The formulas:
fitness(t) = Σ [ load_i × e^(-(t - t_i) / 45) ]
fatigue(t) = Σ [ load_i × e^(-(t - t_i) / 15) ]
form(t) = fitness(t) - fatigue(t)
Your form — your actual readiness to perform — is the difference between these two curves. When fitness exceeds fatigue, you feel strong. When fatigue exceeds fitness, you feel terrible — even if your underlying fitness has never been higher.
Why This Matters More Than "How Do You Feel?"
Most fitness apps ask how you feel and leave it at that. The problem? Subjective feeling is a lagging indicator. By the time you feel overtrained, you've been accumulating excess fatigue for days or weeks.
The Banister model is a leading indicator. It computes your form mathematically from your actual training loads — before you feel it.
Every time you log a session, WodPilot recalculates your fitness, fatigue, and form values using your complete training history. When form is dropping — even if you feel fine — WodPilot knows trouble is coming. When form is rising after a deload — even if you don't feel "ready" yet — WodPilot knows you're primed to perform.
The Supercompensation Window
This is where the model gets powerful: it predicts the best time to push hard.
After accumulated training followed by a deliberate reduction in load, your fatigue drops fast (15-day decay) while your fitness drops slow (45-day decay). There's a window — usually 7–14 days after a deload begins — where the gap between fitness and fatigue is at its maximum.
This is the supercompensation window. It's when PRs happen, competition performances peak, and benchmark retests show the biggest improvements.
A Real Example
Here's what your curves might look like across a 12-week block:
Weeks 1–4 (Accumulation)
- Fitness: Rising steadily from baseline
- Fatigue: Rising, but manageable
- Form: Slightly positive — you feel good, training is productive
Weeks 5–8 (Intensification)
- Fitness: Still climbing (45-day decay means earlier work still contributes)
- Fatigue: Spiking from heavier loads
- Form: Dropping — you feel more tired despite being fitter
Late Week 8
- Fitness: Near peak
- Fatigue: At peak
- Form: At its lowest — this is where you feel terrible despite being objectively fitter than ever
Weeks 9–11 (Peaking + Taper)
- Fitness: Still high (slow 45-day decay)
- Fatigue: Dropping fast (quick 15-day decay)
- Form: Rising rapidly — the supercompensation window opens
Without the model, week 8 is where athletes panic. "I feel terrible, I must be doing something wrong." They either push harder (making it worse) or quit (missing the payoff). With the model, week 8 is expected. It's the valley before the peak. WodPilot won't let you bail on the plan when the science says you're exactly where you need to be.
Five Ways WodPilot Uses the Banister Model
- Real-time form calculation — recalculated after every logged session
- Load prescription — higher form means more aggressive prescriptions; lower form means the system moderates automatically
- Deload timing — the model informs when your fatigue curve is outpacing fitness gains
- Peak timing — for competition prep, WodPilot uses the model to time your taper so fitness-fatigue gap is maximized on game day
- Return-to-training — after a break, the model shows exactly how much fitness has decayed and how much fatigue has cleared, powering the ramp-back protocol
The Research
- Banister et al. (1975) — proposed the original fitness-fatigue model, demonstrating that performance could be predicted from the mathematical interaction of positive and negative training effects.
- Morton et al. (1990) — refined the model's parameters and validated it across multiple sports, establishing the decay constants still used today.
- Busso et al. (1997) — showed the model could accurately predict performance responses in competitive swimmers.
- Mujika et al. (1996) — used the model to optimize taper strategies for Olympic swimmers.
The Bottom Line
Your body is keeping score. Every workout adds to both your fitness and your fatigue — but they don't rise and fall at the same rate. Fitness builds slow and lasts long. Fatigue builds fast and clears fast.
The gap between them is your form. And without tracking it, you're flying blind.
WodPilot runs the Banister model on your training data every day. It knows when your form is rising and prescribes accordingly. It knows when fatigue is outpacing fitness and pulls you back. And it knows exactly when to taper so you peak — not crash.
You don't have to understand the math. You just have to show up. We'll read the score.
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