I Spent Six Months Chasing a Faster Lap. I Came Up Short. Here’s What the Data Showed.

Ten timed efforts, six months of WHOOP data, and the lessons I learned along the way.

Photo by Janusz Walczak on Unsplash

Two goals. Six months. No race on the calendar, no coach, no one to disappoint, but myself. I wanted to get there and pay attention to what the body actually did along the way.

It was late March. I laced up, walked to the start of my 2.7km (1.67 miles) neighborhood loop, and set the timer. The loop has about 50 meters of elevation gain. I’d run it 100s of times over the previous six months in various heart rate zones.

I crossed the finish line at 10:28.

The goal was under 10 minutes. My VO2 max had peaked somewhere around 55–56 over the block. The target was 58, WHOOP’s threshold for “Superior.” Both goals: missed.

I was a little deflated for about ten minutes, and then genuinely fine. Because what I got out of those six months wasn’t the numbers I was chasing. It was something more useful: a clearer understanding of how my body actually responds to structured training. This article is about that.

The Setup

I came into this from three years of Zone 2 running built around mountaineering prep, 125 to 135 bpm, three to four days a week, calibrated for 10 to 14-hour days in the mountains. I’m 36, and the goal was always the mountain, not the clock. When the mountaineering season ended in autumn 2025, I wanted to try something different: a structured, periodized training block with real hard days and real easy days, focused on getting faster.

The lifestyle cost of switching was essentially nothing: same morning slots, same rough duration. The only thing that changed was the intent behind each session.

I set two concrete targets:

1. Run my 2.7km neighborhood loop in under 10 minutes

2. Push VO2 max from ~51 to 58

The training schedule I landed on after watching more YouTube than I’d like to admit:

• Monday: Easy run, ~8km [5 miles] (Zone 2) (3 neighbourhood loops)
• Tuesday: Upper body strength
• Wednesday: Lactate threshold day, rotating between three workout formats (more on this later)
• Thursday: Upper body strength
• Friday: VO2 max intervals, two alternating formats
• Saturday: Lower body or full-body strength
• Sunday: Long run, ~13.5km [8.4 miles] (Zone 2) (5 loops)

Four runs a week. Two genuinely hard. The plan was clean on paper.

The test was simple: every few Fridays instead of the interval session, I’d run one lap of the loop at full effort and record the time. I was using a basic watch that tracked lap splits and nothing else. All the real metrics, heart rate, recovery score, and strain, I reviewed on WHOOP after each run. No live tracking while moving. Just legs and a timer.

The Results

Here’s what the data looked like over the block:

Ten test runs, six months. The goal line sits at 10:00. Getting close , but not there. The chart created by the author.

Roughly 35 seconds of improvement over six months. Respectable progress, but not the goal.

Lesson 1: Easy Runs Truly Need to Be Easy

I knew this going in. The evidence is everywhere, the coaches all say it, and I still failed at it. Repeatedly.

I’d be feeling good on a Monday morning, legs loose, weather nice, and I’d just run a little faster. Nothing dramatic, just a bit above Zone 2, maybe Zone 3. Felt fine in the moment.

Honest version: I knew I was doing it. I’d watch the heart rate creep up and tell myself it was fine, and most of the time it was, in the sense that nothing immediately broke. I was enjoying the moment too much to back off.

Within two or three weeks, I’d feel it. Sluggish recoveries. Heavy legs. Then I’d open WHOOP after the run and see recovery scores that made me wince. The body was sending clear signals that I was spending energy it needed for the hard sessions. I’d deload, recover, feel good again, and then do the same thing.

The honest version of this lesson isn’t “keep it easy.” It’s: you will keep failing at this until you accept that feeling good on an easy run is not an invitation to go harder.

To put a number on what the easy days are actually protecting against, I went back and isolated the cost of Zone 4+5 minutes specifically.

Left: 7-day rolling averages of daily Zone 4+5 minutes and HRV. When the red line climbs, the navy line trends down. Right: estimated causal effect of an extra 10 minutes of Zone 4+5 on HRV measured the same night, one day later, and two days later. The chart was created by the author.

The right panel is not a correlation. Across six months, almost everything moves together: fitness, load, sleep, and baseline HRV. To get past that, I used a causal inference technique that first removes the shared confounders from both variables, training progression, my 7-day prior HRV baseline, prior-night sleep, and Zone 4+5 minutes at the other lags, and then estimates the effect of Zone 4+5 on what’s left. It’s the closest thing to a causal estimate you can pull from observational data.

Each bar describes a different night’s HRV, not the same night re-measured. Together, they trace the recovery curve. A single 30-minute Zone 4 interval session (3 x 10 min of Zone 4+5) leaves a footprint roughly like this:

• Same night: HRV ~13 ms below where it would have landed.
• One day later: ~15 ms below. The deficit actually widens before it heals.
• Two days later: ~11 ms below.
• By night three or four, mostly back to baseline.

Three nights of suppressed recovery from one hard session. Now stack another hard session two days after the first, which is exactly what Wednesday tempo plus Friday intervals does. Friday’s session lands on top of a curve that hasn’t returned to zero yet.

Lesson 2: Vitamins Matter More Than You Think

About a month into the block, something felt off. My resting heart rate was creeping up, not just after workouts but on rest days when I wasn’t running at all. HRV was dropping. Then came the heart palpitations: infrequent, strange, impossible to ignore. My easy runs felt anything but easy: times that should have been comfortable were coming in slow, with a heart rate that wouldn’t cooperate. I was doing everything right on paper, but my body felt like it wasn’t recovering from anything. Like something was missing, and I couldn’t name it.

I was thinking, very clearly, that something had to change, and soon. Whatever I was doing was not getting me through to March. If I kept going on the same path, I was going to burn out, or worse, get hurt.

My first guess was magnesium. It’s a common one for athletes, the research supports it, and to be fair, it did help.

The chart was created by the author.

It wasn’t until late in the block that I stumbled toward the real culprit: B vitamins, specifically B6 and B12. I started taking a multivitamin powder every morning and eating more foods rich in both. The change was immediate and unmistakable. My next easy run just clicked: pace faster, heart rate lower, legs lighter. It wasn’t a subtle improvement. It felt like switching from a bad night’s sleep to a good one.

The clearest proof came a few days later. I went out for a planned 5-lap long run, 13.4km, Zone 2. I felt so good, I ran 7 laps. Two extra, unplanned. My legs were just carrying me, Zone 2 touching Zone 3, in stretches peaking above it. I knew in the moment it would probably cost me a day or two or five of extra recovery, and it did. But it was the first time in months I had physical proof that something had shifted, not just in the numbers but in how the run felt from the inside.

I wish I’d figured this out in October instead of February. I can’t say with certainty that B vitamin deficiency was causing all of it, but the before-and-after was clear enough that I’m not going to ignore it.

Lesson 3: Progress Is a Staircase, Not a Ramp

Around week 4 or 5, my legs were absolutely wrecked. Not sore, just heavy in a way that made sticking to the schedule impossible. I didn’t have a deload plan baked in. That week of forced pullback was the moment I realized: without some kind of regular recovery window, this block was going to fall apart. After that, I aimed for a deload roughly every 4 to 5 weeks. Not rigidly structured, but in that range.

I expected my lap times to drop steadily. A few seconds per week, reliably trending down. Instead, flat for weeks, then a meaningful drop, then flat again at the new level.

What’s interesting, and this repeated enough that it stopped feeling like a coincidence, is that the drops almost always came right after a deload week. I’d rest more than usual, reduce load, and then come back and run noticeably faster.

The chart created by the author.

The body absorbs training during recovery, not during effort. I knew this intellectually. Watching it happen in my own data made it real in a different way. Especially because those deload weeks often felt like I was losing fitness, like I was going backward. If I wasn’t out there running hard and putting in the full week, I was convinced I was losing what I’d built. That feeling was hard to shed. The lesson, eventually: deloads are not just necessary, they’re where the work pays off.

Lesson 4: Aerobic Fitness Improved More Than Top-End Speed

My tempo run pace, sustained Zone 4 effort, went from roughly 13:15 min/loop to around 12:00 min/loop at the same heart rate over those six months. That’s a real, consistent improvement. My easy run pace at Zone 2 moved similarly. I felt aerobically stronger.

My max-effort lap time moved from 11:03 to 10:28. Meaningful, but proportionally much less than the tempo improvement.

The WHOOP VO2 max number tells the same story in a different language. I started at 51 to 52, briefly touched 55 within four to six weeks of training, then slid all the way back down to 51 from mid-October through December alongside the HRV bombing and the climbing resting heart rate from Lesson 2. Things picked up again in mid-January, and by late March, I had one week at 56. That was the peak. The target was 58.

(WHOOP’s VO2 max isn’t a lab measurement, and the week-to-week noise is real.)

The shape of that curve lines up with everything else: a brief early bump, a long winter dip while my body was clearly under-recovered, a rebound once the B vitamin issue resolved, and a ceiling that just never broke through. Whatever was holding the top end back, I’m now reasonably confident it had two parts. The first was months of compromised recovery, which probably cost me real adaptation time. The second was that even after recovery came back online, two Friday interval formats in rotation may simply not be enough VO2 max-specific stimulus to push the ceiling. Not enough volume, not enough variety, not a long enough runway after the body was healthy again.

For the next block, I’ll be curious whether that aerobic foundation eventually unlocks more top-end speed, or whether I need to attack the problem differently. More VO2 max work, started earlier, with a body that’s already healthy.

Lesson 5: Rotating Workout Formats Helps

The schedule had built-in variety: three Wednesday tempo variations and two Friday interval formats, rotated throughout the block.

Wednesday options:

• Workout A: 30–35 min sustained Zone 4 (classic tempo)
• Workout B: 40–45 min progressive run, Zone 2 climbing to Zone 4
• Workout C: 3 x 12–13 min (one loop) Zone 4 intervals with 2 min rest

Friday options:

• Workout A: 6 x 3 min Zone 5 with 2–3 min easy recovery
• Workout B: 4 x 4 min Zone 5 with 3–4 min recovery

This kept the training from feeling monotonous across six months, which matters more than it sounds. But the more interesting finding is that Workout C on Wednesday became my clear favorite, and I think there’s a real reason why.

When I ran 30 straight minutes of tempo, pacing was a gamble. Start too fast, fade in the second half, lose the quality of the session. With the 3 x 12 format, every 12-minute block could be executed properly because the two-minute recovery actually meant something. The total work was similar, but the quality was higher.

The variety isn’t just about keeping things interesting. The right variation can actually let you train harder.

Lesson 6: Nutrition Around Hard Sessions Is Not Optional

I generally eat on the lower-carb side. Works fine for my day-to-day life, works fine for Zone 2 running. For tempo runs and VO2 max intervals, it does not work well.

I tried to put a number on this with the test runs. The result was a useful lesson in what data can and can’t tell you.

The chart created by the author.

In other words, with only ten test runs, the chart can’t prove that fueling helped. The honest read is that most of what looked like a fueling effect on max-effort lap times was probably fitness improving over the block.

But I want to be careful not to read “CI crosses zero” as “no effect.” Let’s take a look at what the adjusted estimate actually implies. The controlled number is +0.33 seconds slower per hour fasted. If I eat dinner at 6 pm and run at 7 am, that’s a 13-hour fast, which translates to roughly 3 to 4 seconds slower on the lap. With 10 data points, I can’t confirm that, but if the point estimate is in the right neighborhood, three to four seconds on a 10-minute effort is not a rounding error. You’d feel it, especially near the end.

But the test runs were never the whole story. The clearer evidence was qualitative, on tempo and interval sessions. It took me a few weeks into the block to accept this, and a few more weeks to actually do something about it consistently. What ended up working: some carbs before the two hard sessions, fruit, a Larabar, and occasionally a square or four of chocolate. And electrolytes and more carbs within an hour after.

The difference in session quality and (perceived) recovery was meaningful. On the mornings I showed up to a tempo run properly fueled, I felt I could execute. On the mornings I showed up on fumes from my normal eating pattern, the session typically felt harder.

Standard advice, I know. But there’s a difference between knowing something and actually organizing your week around it.

After The Last Lap

Six lessons. Two missed goals. One last lap.

The final test run on March 27th, 10:28, was genuinely satisfying despite missing the goal. Not because I’m the kind of person who’s easily satisfied with “close enough,” but because I knew the gap between where I ended and 10:00 was no longer a mystery. It wasn’t the effort. It was a few specific things I now understand how to address.

I started at 11:03. I didn’t hit 10:00, but I finished with a clearer picture of my own physiology than I’ve ever had.

Failing a well-structured goal teaches you more than never having the goal at all. The keyword is well-structured: it means the failure comes with data, and the data comes with lessons, and the lessons give you a better starting point for the next attempt.

Sub-10 is still on the list.