Six weeks of zone two training—and nothing else—can feel like an eternity of slow, sweaty mediocrity.
But what if that boring, conversational-pace cardio actually rewrites your metabolic fitness in ways high-intensity intervals can’t?
Cyclist and content creator Manon Lloyd recently put zone two training to the test, committing to six full weeks of low-intensity rides with zero hard efforts.
Her results? A 15% improvement in lactate threshold and a metabolic transformation that surprised even her coach.
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What Exactly Is Zone Two Training?
Zone two training refers to exercising at low intensity—typically where heart rate sits between roughly 60-70% of maximum.
It’s the pace where conversation flows easily, sweat might not even break, and effort feels almost too easy.
For Lloyd, that meant holding her heart rate between 150-155 beats per minute during rides—a narrow five-beat window that required serious discipline.
It doesn’t feel like I’ve been training. I’ve not done any hard efforts. I’ve not reached my max. It’s just a really weird position to be in.
Despite coming from a background as an elite athlete, Lloyd found sticking to zone two surprisingly challenging—especially outdoors.
Six Weeks of Disciplined Low-Intensity Work
Lloyd’s training plan, designed by Coach Laurence, ramped up gradually over six weeks.
Ride durations ranged from one hour to just over three hours, with her biggest week totaling nine hours on the bike.
She completed roughly 80% of rides indoors on a trainer—where maintaining zone two proved far easier than navigating hills and traffic lights outdoors.
Structured Intervals Within Zone Two
To combat boredom, Coach Laurence added interval structure within zone two sessions.
A typical 90-minute indoor session might look like:
- 10-minute warm-up
- 20-minute block at top of zone two (150-155 bpm)
- 5-minute rest
- Repeat 3-4 times
This approach broke up monotony while keeping intensity strictly controlled.
Did She Actually Stay in Zone Two?
Coach Laurence analyzed Lloyd’s uploaded ride data and found she stayed impressively consistent.
Half your training was in zone two, another 25% in zone one. Almost 95% of training was below lactate threshold—which is the top of zone two. Absolutely heaps of time in that zone, which is what we’re looking for.
Critics on social media pointed out brief spikes into zone three, but Laurence dismissed concerns.
Absolutely not. There’s no really hard line. The body doesn’t work like that. It’s a bit of a transition. If you think about going up a hill, it’s pretty impossible to stay in zone two exactly.
Short excursions out of zone two—at traffic lights, hills, or transitions—don’t sabotage adaptations.
Lab Testing Reveals Dramatic Improvements
After six weeks, Lloyd returned for lab testing: a step test measuring blood lactate at increasing intensities, followed by a ramp test to failure.
The results were striking.
Blood Lactate Curve Shifted Significantly
Lloyd’s blood lactate curve—a key marker of metabolic efficiency—flattened dramatically compared to six weeks prior.
Last time, there was never really a level bit of line. It just went up. This time, a lot better. You can see a nice flat line where you’ve got two stages, which is really good. And it’s also a lot lower than before—last time it went up to sort of 9 millimoles, this time it’s peaked out significantly lower, around 6 millimoles.
Lower lactate at given intensities means better aerobic efficiency—muscles rely more on fat oxidation and less on glycolysis.
Lactate Threshold Jumped 15%
Lloyd’s lactate threshold—the intensity above which lactate accumulates rapidly—increased from 140 watts to 160 watts.
That’s a 15% improvement in just six weeks.
Her zone two training power also rose by roughly 20 watts, meaning she could sustain higher output while staying aerobic.
VO2 Peak Improved Modestly
Maximal oxygen uptake (VO2 peak) increased by about 7-12%—a solid gain, though smaller than threshold improvements.
Coach Laurence explained this makes sense given training focus.
If you would have done more top-end stuff, I think we probably would have seen a bigger shift in aerobic capacity, maybe a bigger shift in your four to ten-minute power output, and probably less of a shift in your thresholds.
Zone two training targets peripheral adaptations—mitochondrial density, capillary growth, fat oxidation—not central cardiovascular capacity.
Why Zone Two Works: Adaptations Explained
Low-intensity training triggers unique physiological changes:
- Increased mitochondrial density: More “power plants” in muscle cells
- Enhanced fat oxidation: Body becomes efficient at burning fat for fuel
- Improved capillary networks: Better oxygen delivery to muscles
- Greater aerobic efficiency: Less reliance on glycolysis, reduced lactate production
These adaptations come from duration, not intensity.
There’s different mechanisms for low-intensity adaptations. It’s about the duration, not the intensity. There’s a minimum intensity, after which it’s about how long you go for. Going harder doesn’t actually lead to any more adaptation when you’re riding easy.
High-intensity intervals improve VO2 max and top-end power but don’t build the same aerobic base.
Training to Heart Rate vs Power
Lloyd trained using both heart rate and power—a critical combination.
Coach Laurence noted that heart rate zones stayed relatively constant even as fitness improved, while power zones shifted upward.
Your heart rate and your zones kind of stay the same. The fact you trained to heart rate as well as power—if you just trained to power, you’d actually have been training now 20 watts too low.
Using heart rate ensures you’re hitting correct physiological intensity, regardless of fitness changes.
What Happens After Six Weeks?
Could Lloyd keep improving with more zone two training?
Probably—but with diminishing returns.
You started from a level which wasn’t the highest. You’ve got a really good block of training—33 to 35 hours—which is awesome. If you were to continue, you probably would see much smaller improvements. Now it’d be the time to go, okay, what next? How do you overload and stress the body?
Options for continued progress include:
- Extending ride duration: Build up to 10-15 hours per week with longer sessions
- Adding intensity: Incorporate threshold or VO2 max intervals
- Periodizing training: Alternate blocks of base building and high-intensity work
Six weeks establishes foundation; additional overload drives further gains.
Key Takeaways for Anyone Trying Zone Two
Lloyd’s experiment offers practical lessons for recreational athletes:
- Zone two works—even for trained athletes: Elite backgrounds don’t prevent significant gains
- Indoor training improves compliance: Trainers make holding steady intensity easier
- Small zone excursions don’t matter: Brief spikes into zone three won’t ruin adaptations
- Heart rate + power is ideal: Combining metrics prevents training drift
- Intervals within zone two combat boredom: Structured blocks make long rides mentally manageable
- Six weeks shows results: Meaningful improvements appear relatively quickly
Most importantly: zone two feels too easy—and that’s exactly the point.
Adaptations come from accumulating volume at sustainable intensity, not from grinding through intervals.
I’m actually really surprised with how much that has changed, because five and a half, six weeks is not a long time. And when you’re training at such a low intensity, it’s hard to get your head around how you’re going to get fitter and better. In my head, to get fit you have to be going full gas all the time—which isn’t necessarily the case, as we’ve proven.
Lloyd’s 15% lactate threshold improvement proves that boring, conversational-pace training builds metabolic fitness that intervals can’t replicate.
For endurance athletes seeking aerobic base, zone two deserves serious attention—even if sweat never breaks.
