The January Blues

You’re currently reading a draft.

This is a blog on how I interpret metrics to calibrate my January training. If you weren't highly trained and/or didn't take much time off this probably won't be very helpful. But for the few who fit those criteria, this may help. Feel free to tell me my implementation of these metrics is wrong, this is just what works for me!

The Confusion is Real

Like many of you, I swore I'd end the 2025 year strong. Like many of you, I took way too much time off (nearly the entire month of December). After Leadville (you can read more about that story here, and more posts are coming in the next few weeks), my training volume tapered down hard. By December, riding was sporadic at best. Some rest was intentional. Some of it just… happened.

For context, as I've written elsewhere, my FTP about a month after Leadville (with very little training between the race and the test) was 322 watts (4.3 watts per kilogram, normalized power of 338 watts for 20 minutes). After Leadville I spent very, very little time in anything other than Zone 2 and some tempo / sweet spot. After the FTP test, I spent even less time in any zone at all, as you can see.

Now that January has rolled around, like many I had anxiety:

• How much fitness have I lost?
• What might my FTP be right now?
• Should I adjust my zones?
• Should I just give up because I took a month off and I'll never be fit again?

As always the answer is just get back on the bike; rip off the band-aid. As I did that some efforts felt hard, some felt comfortable and similar to me pre-time off self. An FTP test at this point feels entirely useless because it will change so fast.

This is the part of early season that confuses many athletes. So what to do?

Fitness Isn't a Single Number

All (amateur) cyclists anchor too much on FTP. The bias then is to assume "I took time off, so my FTP is lower, so my zones to use for training are lower". The data doesn't actually support that in all cases though. What I want to do here is present a simple framework for how to get your year started without having to do an FTP test that will be stale in a few weeks, and without having to stress over if you're training too hard or too easy. Fitness doesn't shed equally across zones.

We don't lose fitness like a dimmer switch on a light: if your FTP is 300 in December, your FTP doesn't decline predictably according to any linear/exponential decay equation, and your zones certainly don't either.

We tend to lose fitness in layers (I'm sure there is some science to this, but for now I'm anchoring purely on anecdata from myself and many others):

• Base fitness is durable
• Tempo gets harder but hangs on surprisingly well
• Threshold durability is fragile and disappears first

Two Metrics to Recalibrate

Instead of asking “what is my FTP right now?”, I’ve found it far more useful to ask two different questions to get to the right answer for my training early in the year:

1. How efficiently am I producing power?
2. Is my cardiovascular cost stable at a given intensity?

This is where two metrics that you've probably seen in TrainingPeaks but haven't spent any time thinking about come in: Efficiency Factor (EF) and Pwr:Hr.

Efficiency Factor (EF)

A simple ratio of power to heart rate. Importantly, EF is only meaningful when compared to your own historical values at the same intensity; absolute EF numbers aren’t comparable across athletes (also be aware of your own day to day variability in heart rate due to hydration, caffeine, sleep, etc.).

EF helps answer:

How much does it cost me to ride at this intensity?

When fitness is good EF is high and it holds steady over time. When fitness is missing EF drops late in intervals. Note the trend over intervals matters.

Pwr:HR (Decoupling)

This looks at how heart rate trends relative to power over time. Essentially, Pwr:HR rate helps answer: can I actually sustain this effort or am I borrowing energy from systems in order to do so? When you have low drift, you're performing stable work. When your Pwr:HR is rising (across a workout or across intervals), you're above what your system can support. Where this happens matters: below MLSS (e.g. tempo), rising Pwr:Hr often reflects durability limits; at or above threshold, rising Pwr:Hr means the effort is no longer sustainable.

Using EF and Pwr:HR Together

When EF is high and Pwr:Hr is low, the effort is both efficient and sustainable. This is where good Z2/tempo/true threshold work live. When EF is high but Pwr:Hr is rising, we can still hit the power but we're borrowing from durability; this is often what January “threshold” looks like (as I'll show). When EF is low and Pwr:Hr is rising, the effort is expensive and I’m above what my system can support. Finally, when EF is low but Pwr:Hr is flat, heart rate has likely saturated; the effort may look controlled, but I’m operating at a ceiling vs. equilibrium.

Technical nuance: a key thing that shows up later in the post - these metrics are interpreted differently depending on intensity. Below MLSS (Zone 2 and tempo), some rising cost is acceptable and reflects our durability. At MLSS (threshold), rising cost is disqualifying as it means the effort is no longer threshold.

You can read more about both of these from TrainingPeaks here.

What This Data Looks Like

In order to add some more teeth to this very academic description of two metrics that TrainingPeaks has concocted, I want to illustrate how this looks in practice and how I then interpret the data to make a plan for my early weeks of the year.

What I'll do is compare my FTP fitness (workouts from last year when I was around my last FTP test result) to my reality right now using real workouts. Throughout the examples below, I’ll sometimes refer to both metrics at the interval level and sometimes at the whole-workout level; both are useful, but they answer different questions as is probably self evident based on the definition.

Zone 2 Fitness

For this, I've picked a 2 x 30 minutes high Zone 2/low Zone 3 workout from August and a 2-hour Zone 2 ride I performed on the trainer on January 4th. For reference at my September FTP my Zone 2 range (according to the Coggan model for calculating power zones, not using lactate) is 180-243 watts.

How to Interpret This:

• In August, heart rate fell relative to power despite sustained high-aerobic work which is indicative of deep aerobic durability; this was obviously peak fitness (exactly 20 days after Leadville) and I could sustain this for a very long time (if properly fueling, etc. - the 30' efforts were at ~260 watts).
• In January, my heart rate remained extremely stable at the Zone 2 intensity. I wasn't quite as fit as August, but even after reducing volume through the fall and taking weeks totally off I was still able to produce power, and...
• In both cases, my EF was similar and my decoupling was well below 5%. Yes, I lost some fitness but in both cases it's true that there was essentially no cardiac drift across the workout - my heart rate was flat instead of needing to work harder as the workout progressed that the same intensity.

I take this to mean that ~230-240 watts is my correct Zone 2, which aligns with the high end of the Zone 2 range in Coggan's model for a 322 watt FTP! Even though I reduced volume and took time off my base is still very strong! As I start riding again in January I should be confident in my "old" Zone 2 range.

Tempo

To evaluate where I am at for Tempo work I've chosen to highlight a 2 x 20' tempo workout from September as well as a 3x15' tempo ride with 5 minutes rest (including a 20 minute warm up, 10 minute build up to VO2 for 1').

How to Interpret This:

• In September, tempo was highly repeatable and metabolically cheap
  • High EF (1.83 overall, ~1.86 per interval)
  • Minimal drift even across 2×20 minutes
• In late December, absolute tempo power was only slightly lower
  • Interval power nearly matched September
  • But cardiovascular cost rose steadily across reps
  • EF was lower at the same power (higher heart rate for the watts)
• The key difference isn’t power here it’s my durability at Tempo
  • Pwr:Hr more than doubled across the December intervals
    • They required more effort as they went on vs. September
  • EF decayed interval to interval instead of holding steady

The major difference is durability of Tempo efforts. My absolute tempo power is largely intact, but my ability to sustain it economically has eroded.

In practice, my hypothesis is that means I don’t need to lower my tempo targets. I can still ride at ~265–275 watts (the middle of my Zone 3, which tops out around ~290). What has changed is how I judge success. For January, I’m using tempo as a bridge: riding the same watts as peak fitness from the season, but evaluating the session by whether how EF holds and Pwr:Hr drift decreases across reps not by how easy it feels. As long as I keep RPE in check and avoid pushing into threshold, ~270 watts remains appropriate for tempo, in my opinion.

You might ask "If Pw:Hr is rising, why don’t you lower tempo watts like you did threshold?” You'll see I do this for Threshold, but not Tempo - I explain below.

Threshold

For this final example: threshold. I've chosen the last high intensity threshold workout I did before Leadville at the end of July. This was 3 x 18 minutes with 10 minutes rest. For this workout, it was performed outside of Boulder, Colorado, so each interval was done over 6,500 feet and the last one ended around 9,000 feet in elevation (hence the lower absolute power numbers for July), but you get the idea. The current workout is a 3 x 6 minute threshold workout at sea level a few days ago. This really shows where fitness was lost in late 2025, in my opinion.

How to Interpret This:

• In July, threshold was a place I could live for a long time
  • Long intervals (~18 minutes)
  • Heart rate rose at the beginning of the effort and then stabilized
  • Power was repeatable without escalating metabolic cost
• In January, threshold is now a place I can only visit
  • Shorter intervals (6 minutes)
  • Heart rate never settled
  • Each interval required increasing cardiovascular strain

The intervals are not equivalent. Threshold is never boring and it always hurts, but in July I could sit there for a long time without increasing cost. Just a few days ago I couldn't. The nuance here is we can see lower decoupling and worse efficiency at the same time. Lower decoupling is only good if EF is stable. In January decoupling fell, EF continued to fall, and HR starts and stayed high. I was operating too hot for a true Threshold session and it wasn't sustainable. Combined these are a signal that I'm hitting a ceiling vs. settling into an effort that is truly at Threshold - my power target based on FTP is too high for now.

For now, true threshold lives lower, probably closer to ~325–330 watts (although I have yet to test this hypothesis in a workout), not because my ability to produce the watts is gone, but because my body's ability to sit at the edge went away.

Technical nuance: the different interpretation in tempo vs. threshold is because of where they sit relative to MLSS. Below MLSS (tempo), rising cost is acceptable and reflects durability, but at MLSS (threshold), rising cost means the effort is no longer sustainable and the watts are too high and we risk blowing up entirely.

MLSS, or maximal lactate steady state, is roughly the hardest effort where the body can still keep up without cost escalating continuously. Above MLSS things get harder and harder (legs hurt more and more) until we reach failure.

VO₂

I haven't yet performed a VO2 workout this year, but it's interesting to contrast the behavior of Efficiency Factor and Pwr:HR during a VO2 workout performed over the summer around peak fitness (a few days before the threshold workout I mentioned above) and then the threshold workout that I did just a few days ago.

My threshold workout from a few days ago doesn't look like a VO2 workout but it also doesn't look like a Threshold workout. January threshold was not VO₂ but it was closer to VO₂ than to true threshold! January threshold looked calm inside individual intervals but only because my heart rate had already reached it's ceiling for the power. When viewed across the entire session, efficiency continues to fall and cardiovascular cost keeps rising. That combination of stable power, falling efficiency, and rising baseline heart rate is the signature of work above MLSS (maximal lactate steady state - more or less the hardest effort where the body can still keep up) rather than a steady threshold effort. I was training tolerance above threshold. For now, I see this as more evidence that my true threshold needs to move lower until heart rate can rise and then settle.

How to Use This Data

Okay, so what’s the point of all this?

The simple answer is that I use EF and Pwr:HR to help me avoid training too hard or too easy while I'm in the process of reestablishing fitness. Right now, my aerobic base and tempo fitness are still there, so those targets don’t need to change. What has changed is my ability to sit comfortably at the very edge of true threshold so I’m treating threshold as if my FTP is temporarily lower.

In practice, that means I keep my Zone 2 and tempo watts the same, but I bring my threshold targets down slightly and judge success by how stable the effort is at Threshold RPE, not how heroic it feels. Over the next 4–6 weeks (and possibly up to 8), I’ll watch how efficiency and heart-rate drift behave from workout to workout. When threshold starts to feel hard and stable again, I’ll know it’s time to push those numbers back up and eventually retest FTP to recalibrate.

The upside of thinking about training this way is that I don’t have to constantly FTP test (which is miserable), and I avoid the two biggest January mistakes: riding Zone 2 and tempo a little too easy, or turning every threshold workout into an accidental VO₂ session. It works for me, I hope it helps someone else too.

Wrap Up

So the point is the January Training Blues don't need to be so hard. Getting back on the bike after time off doesn't have to be anxiety-inducing. Yes, we've lost fitness but it's not the end of the world. We can recalibrate and maximize our early weeks until we start to get back into a groove and reestablish fitness.

Key takeaways:

• FTP isn’t lost evenly across zones
• Base and tempo often return before threshold durability
• EF and Pwr:Hr tell you more than an FTP test in January
• Forcing numbers too early slows the rebuild
• Stability is the signal that fitness is coming back

Fitness isn't gone; it's just a little bit more uneven. Understanding that can make January training a lot more productive, particularly in trained athletes.