Fitness, Fatigue and Form Explained for Cyclists

James. You're listening to the WattPlan Podcast, and I'm James. Family, a day job, the very occasional podium, the small matter of building WattPlan, and a habit of reading training physiology papers on holiday. This week, the chart I check more often than I'd like to admit. Three wiggly lines called Fitness, Fatigue and Form. How do you actually read them? Lyra is our AI research voice, and every study we mention is linked in the show notes.

Lyra. Read them as two averages and the gap between them. Fitness is your daily Load averaged over about six weeks, so it moves slowly. Fatigue is the same thing over a week, so it jumps about. Form is Fitness minus Fatigue. Train hard and Form goes negative. Ease off and Fatigue falls faster than Fitness, so Form climbs.

James. So negative Form is bad. I see minus twenty and I get twitchy.

Lyra. It isn't bad, and that's the one people panic about. Negative Form in a training block just means you've been working. WattPlan calls minus ten to minus twenty five Building, and only reads Tired below that. From minus ten to plus five it reads Ready, and above plus five, Fresh.

James. Where did this whole idea come from? It looks like somebody's spreadsheet.

Lyra. Not far off. We looked at two studies for this. The first is a 1990 paper in the Journal of Applied Physiology by Morton, Fitz-Clarke and Banister. They modelled every training session as producing two effects at once, a fitness response and a fatigue response, each fading away exponentially when the training stops. Combine them and you get a prediction of performance. [1]

James. And did the prediction hold up, or is it just neat maths?

Lyra. It held up well against measured performance, both while people were training and while they tapered. That's exactly why tapers work on the chart. Fatigue drains in days, Fitness over weeks, so a lighter week lets Form rise while most of your Fitness stays put.

James. Right, so Form's the magic number. Get it to the perfect value on race day and I fly.

Lyra. I'd push back on magic. The second study shows why. It's a 2003 paper in Medicine and Science in Sports and Exercise by Thierry Busso. Six previously untrained people trained for twelve weeks of a fifteen week study, and their five minute power was tested three times a week, so he had a lot of data on very few people. [2]

James. Six people. That's a pub team, not a study. Go on, though.

Lyra. They improved by about 30 percent, which is roughly what beginners do. The interesting part is the model. A version where the fatigue from each session grew as the training piled up fitted their results better than the fixed version. And it showed an inverted U. More daily training helped up to a point, and past that point performance got worse.

James. And I'm guessing the chart on my phone is the fixed version.

Lyra. It is. It uses the same six week and one week averages for everyone, and it assumes a hundred points of Load tires you the same in a heavy block as in an easy one. That study suggests bodies don't quite behave like that, especially when the training gets big.

James. Then why should I trust it at all, if the maths is that simple?

Lyra. Because the trend is useful even when the detail isn't. Watch the direction over a week or two, not the daily wiggle. Fitness creeping up through a block means the training is adding up. Fatigue sitting high for weeks means those weeks have had no easy spell in them. And Form deeply negative for a long stretch is a reason to ease off before your sessions start failing.

James. What does a good block actually look like on the screen?

Lyra. In the loading weeks, Fitness rises gently, Fatigue rises faster and sits above it, and Form dips below zero. In a recovery week, Fatigue drops quickly, Fitness barely moves, and Form comes back up. WattPlan sizes a recovery week's Load from the Fitness you carry into it, so that dip stays small.

James. How fast should Fitness go up, then? I always want the line steeper.

Lyra. Two to four points a week is a reasonable build. Trying to force it faster is how people tip into overreaching. And steady beats spectacular. A Fitness of 100 you can hold for months is worth more than 120 that ends in illness or burnout.

James. Say I take a week off in the summer and the Fitness line falls off a cliff. Is that real?

Lyra. It's real arithmetic. Each day off takes nearly two and a half percent off Fitness, and that compounds, so a week away looks dramatic. Fatigue drains faster still, which is why you come back feeling sprightly with a smaller number. The line counts the Load you didn't ride. It isn't a scan of your legs.

James. So a big positive Form isn't always good news either.

Lyra. Not for long. A few days of high Form before an event is the point of a taper. Weeks of it mean you're rested, but the Fitness underneath is slowly slipping away.

James. And the dashed line? I've always ignored it.

Lyra. That's the forecast. It starts from your real numbers as of yesterday and runs your planned Load forward, so you can see where Fitness and Form are heading if you ride the plan as written. Miss a week and the next forecast starts from wherever that week left you. That makes it a quick, honest picture of what the rest of the plan will do from here.

James. If you're new to this, though, the whole chart must look like noise.

Lyra. For the first few weeks it mostly is, because it needs history to average. If you're new to structured training, connect the app you already record rides with and bring in your recent riding, then give it a month before you read much into it. And you can ask the Coach what your numbers mean. It can see them.

James. And if you train with power?

Lyra. Then the chart is only as honest as your FTP. Set it too high and every ride scores low, so Fitness reads lower than it should. The same goes for heart rate if your threshold or maximum is out of date. Get those right before you trust any of the lines.

James. And if you race? Surely this is where Form earns its money.

Lyra. If you race, it's useful, with a caveat. Before a big day you want Fitness held up, Fatigue well down and Form positive, a little higher for a short, sharp race than for a long one. But the best value is personal. Note your Form before your best rides this season, and you'll learn your own number better than any table can tell you.

James. What can't these studies tell us?

Lyra. Quite a lot. Busso's model came from six untrained people, and the 1990 work was built around running. The six week and one week constants are averages, and some riders respond faster or slower. And the chart can't see sleep, stress or illness, any of which can flatten you while every line looks fine.

James. So what should I do with it this week?

Lyra. Three things. One, open Progress and look at Fitness over the longest range you can. Free shows the last seven days, Premium up to a year. Is it rising, flat or falling? Two, in your next recovery week, watch Fatigue drop and Form climb, then judge that week by your first hard session after it. Three, before your next big ride, write down your Form, and afterwards, how you rode.

James. So it's a trend line, not a verdict. Watch the direction, learn my own race-day number, and stop panicking every time Form dips below zero.

Lyra. And remember what it's counting. The chart knows the Load you rode, not how you feel. When the two disagree, believe your legs first, then go and find out why.

Lyra. The full article and every study we mentioned are on the WattPlan blog, linked in the show notes. And if you've enjoyed this, follow the WattPlan Podcast wherever you're listening, so you don't miss the next one.

James. And if you want a plan built around the time you've actually got, get WattPlan on the App Store or Google Play. Thanks for listening.

Voices produced with ElevenLabs. James's voice is a clone of his own, Lyra is an AI voice, and James reviews every episode.