Training that
adapts to you.
Kresta is an AI training coach built on the Skiba critical-power model. It reads your rides, runs, gym sessions and wellness, and adjusts your plan when life happens. In development for iPhone, coming soon. Android and web later.
Free while in development.
The AI coach
A coach that knows your training.
It has read every session, your fitness and your wellness. Tell it about your day and it changes the plan, then tells you why.
It knows your history
It sees your Form, your recent hard days and what is coming, and plans around them.
It changes the plan for you
Shorter, easier, moved to tomorrow. The calendar and the Today card update together, and every change can be undone.
One coach for every sport
Rides, runs, gym days, tapers, comebacks.
The adaptive plan
A plan that rewrites itself.
The plan is rebuilt every day from your readiness, your recent load, and what actually happened. These are the rules it follows.
Readiness gates intensity
A strained morning turns a hard day into an easy one. When recovery is back, the hard day comes back.
Hard days keep their distance
Key sessions are spaced apart, and the day before a big one is kept easy.
Layoffs get a ramp
After illness or a break, the first sessions back are capped and build up gradually.
Life edits are one sentence
Tell the coach you only have 45 minutes and the session shrinks to fit. Every change can be undone.
Your signature
Three numbers that describe what you can do.
Kresta fits the three-parameter critical-power model from published sports science to your own rides and runs. No test day needed. Every session is drawn against it.
Critical power, CP
Sustainable Power
in watts
The power you can hold for a long time. The base of everything else.
W prime, W′
Burst Energy
in kilojoules
A limited tank. Work above Sustainable Power drains it, easier work refills it.
Pmax
Top Sprint
in watts
Your peak power. What a flat-out sprint reaches.
Running gets its own signature: Sustainable Pace, the race times it predicts, and Top Speed.
Fitted to you
The curve comes from your best real efforts, from five seconds to an hour.
Predictive
It tracks your Power Reserve second by second, so it knows what a session costs before you start it.
Updated by a Personal Best
Beat the model in the real world and your numbers update on their own.
A planned session, drawn on your numbers. The line above the blocks is your Power Reserve for each moment of it.
The research
The three-parameter critical-power model and the W′ balance it tracks come from Philip Skiba's published work on the expenditure and reconstitution of work capacity above critical power, including in the Journal of Science and Cycling. Kresta's identification, Personal Best detection, and the coaching built on top are its own.
Fitness and readiness
Where you are, and where you are heading.
Three plain numbers from your training, and your wearable's view of this morning. Together they decide what today should be.
Fitness
Your training over the last six weeks. It climbs slowly and drops slowly.
Fatigue
Your last week. It rises fast after hard days and clears fast with rest.
Form
Fitness minus Fatigue. Positive means fresh legs, negative means tired ones.
Readiness from your own baseline
HRV, resting heart rate and sleep from your wearable, compared with your own recent mornings, not a population average.
Pointed at your goal
Set a race and the plan builds toward it, with the Form you should arrive with.
Train
Train inside the app.
Today's session is one tap away, built for your numbers. Ride it indoors on a smart trainer, or head out with GPS.
A workout library
Workouts are generated from your signature, so the targets are always yours.
Indoor and outdoor
Smart trainer control indoors. GPS, pace and route outside. Heart rate strap and power meter over Bluetooth.
Everything counts
Recorded sessions feed the same model as everything else.
Integrations
Connect once.
Rides and runs land by themselves. Sleep and HRV come along.
intervals.icu
One connection for Garmin, Wahoo, Hammerhead and more. Rides and runs sync on their own, with full detail. Coming from Strava? Point your device at intervals.icu and Kresta reads it from there.
Garmin wellness
Sleep, resting heart rate and HRV, via intervals.icu.
FIT, GPX, TCX
Import single files, or your complete history as an export.
Bluetooth sensors
Heart rate strap, power meter, smart trainer.
The philosophy
Adaptation is complex biology. Training is not complicated.
Training is fairly simple: easy workouts, hard workouts, the right balance, individually tailored. The science and your data make it yours, and the coach is there to change and discuss it.
Don't race your intervals
Hard days are for adaptation, not for records. The plan is mostly easy, with the hard days properly hard.
Easy is easy
Easy rides and runs go on heart rate and feel. Leave the watts alone. That is how training stays fun for years.
Feel counts as data
Say how the day feels and the plan listens. Easing off mid-session is not quitting, it is the system working.
Why Kresta
A plan engine and a coach, in one.
Most training apps are either a plan engine you cannot question, or a chat coach with no rules. Kresta is both: a science-backed engine underneath, and a coach on top that can change your plan but cannot break the engine's rules.
Deterministic underneath
Plain sports science: the critical-power signature, the fatigue-shifted curve, updates only from a real Personal Best. Turn the chat off and the engine still works.
Conversational on top
The coach edits the same plan you see. Move things, shrink things, swap sports, undone in one tap. The one thing it cannot do is break the model's rules.
Rules the coach cannot talk past
- Illness and rest status anchor every suggestion, not Form alone.
- Two weeks off running means no hard running, whatever the chat says.
- Key sessions keep their spacing, easy day before included.
- Hard days are budgeted across sports, roughly two a week.
- Readiness from your wearable caps what Form alone would allow.
Honest about what is new
The physiology is published and calibrated. The chat layer is the young part, which is why the rules exist. Not here yet: sending workouts to bike computers, and fueling advice is a conversation rather than a modelled feature. We would rather tell you now.
Coming soon
Kresta for iPhone.
In development and free while it is being built. Android and the web come later. The store links appear right here the day they go live.
Questions, ideas, or a bug? A real person reads every mail.