Zones & Thresholds
Zone 2, LT1/LT2, FTP, CTL/ATL/TSB, polarized vs pyramidal, aerobic decoupling.
30 articles · sorted by most recent
Critical Speed vs Lactate Threshold: Why CS Reads Faster on Average and Which Number to Set Your Paces From
Critical speed ran 0.36 to 0.47 km/h faster than lactate thresholds in 31 runners, about 6 to 8 s/km at a 4:00/km pace. Set tempo from the lower number.
How to Read Your Performance Management Chart in Your First Training Year
Your fitness number is roughly your weekly training load divided by 7. In year one, raise it 2 to 5 points a week, and expect form to sit between -10 and -30 in build weeks.
3-Zone vs 5-Zone Training Model: Which One Are You Actually Using?
The '80% Zone 1' rule comes from a 3-zone model tied to lactate thresholds. Your watch uses 5 zones based on max heart rate. Same label, different meaning: 80/5/15 scores 2.38, 70/25/5 scores 1.15.
Group Ride Intensity Creep: Why Your 'Easy' Ride Is Secretly a Threshold Session
A typical 'easy' club group ride spends 10-25% of its time above FTP and can cost 20-40% more training stress than a solo Zone 2 ride of the same length.
The MAF Test and 180-Minus-Age Heart Rate Method: Does Maffetone's Formula Hold Up to 2025 Research?
180-minus-age tracks a trained runner's real aerobic threshold within about 1 bpm at 25, then undershoots it by roughly 16 bpm by age 65. Here's the data.
Why 80/20 Polarized Training Breaks Down for Recreational Athletes: The Intensity Blindness Problem
Counting the same training week a different way moves your easy-zone share by 17.6 percentage points. Here's why your 80/20 split isn't the number you think, and what to do under 10 hours a week.
The Ingebrigtsen Double-Threshold Method for Age-Group Runners: What the Evidence Actually Supports
Double threshold means two lactate-controlled sessions in one day, not two hard workouts. The 2024 review behind it studied 13 elite runners. Here's what it proves for age-groupers, and what it doesn't.
Watts Per Kilogram Isn't One Number: What the 2025 Research Actually Shows
A 2025 study found the ideal power-to-weight exponent ranges from 0.35 on flat courses to 0.89 on steep climbs, not the flat 1.0 that W/kg assumes.
Chronic Intensity Load vs CTL: The Fix Almost Nobody Uses, For a Problem Everybody Still Has
CTL treats 100 TSS of Zone 2 the same as 100 TSS of threshold work. Chronic Intensity Load (CIL) is a decade-old TrainingPeaks tool built to fix exactly that — here's the math and its real limits.
Cardiac Output vs Stroke Volume: Why Two Athletes With the Same VO2max Race Differently
Two athletes can both post a 55 VO2max, yet one has a 187 mL stroke volume and the other gets there by extraction. Same number, different engine.
Critical Power vs FTP for Ironman Bike Pacing: Which Number to Use Outdoors
Critical Power runs about 7 watts higher than FTP on average, and outdoors that gap can overcook your Ironman bike leg. Here's which number to pace by.
Why Does Running Economy Vary 30% Between Runners With the Same VO2max?
Running economy can vary up to 30% between runners with identical VO2max, enough to separate a 3:05 marathon from a 3:35. Here's what actually moves it.
Critical Speed vs FTP: How the Dual-Sport Threshold Unifies Your Running Pace and Cycling Power Zones
Running critical power overestimates cycling critical power by 20%, explaining just 27% of its variance. One threshold number does not convert across sports.
Why VO2max and Lactate Threshold Both Decline After 90 Minutes (The Dual Squeeze)
By mile 21, your VO2max has dropped 7.1% and your lactate threshold speed has fallen 6.6% — yet your pace is the same. That gap is why marathons fall apart.
Long vs Short VO2max Intervals: What the 2024 Research Actually Shows
4×3min intervals at 95% vVO2max produced 63% more time above 90% VO2max than 24×30s efforts — yet both felt equally hard. Here's what that means for your next hard session.
Anaerobic Capacity (W'): Why Your 30-Second Power Matters for a 4-Hour Race
W' (W prime) is your finite anaerobic reserve above critical power — trained cyclists average 12.7 kJ, and burning it wrong on lap 1 of a 4-hour race costs you the run.
Track vs Treadmill Lactate Testing: Why Your Zones Don't Transfer Surface to Surface
Treadmill lactate tests run 1.0–3.7 mmol/L lower than track tests at the same pace. That translates to threshold zones that are 7–8 s/km off — enough to train in the wrong gear for months.
VO2max Intervals That Fail at the Muscle, Not the Lungs: The Peripheral Limiter Problem
Most cyclists quit VO2max intervals because their legs fail, not their lungs. The Fick equation explains why — and the fix requires knowing which side of the equation limits you.
Sweet Spot Training Is Not Zone 2 and Not VO2max: Why the Middle Zone Is Both Overused and Misunderstood
Sweet spot (88–93% FTP) isn't Zone 2 and isn't threshold. After 8–12 weeks, research shows threshold-heavy training produces zero significant gains in well-trained athletes — here's what to do instead.
How Do I Calculate My Max Heart Rate? Why 220-Age Is Wrong
The 220-age formula was never validated. Its standard error is 12.4 bpm — meaning 1 in 20 people are off by more than 24 bpm. Here's what to use instead.
Why Am I Always in Zone 4? The Most Common Beginner Heart-Rate Mistake (And How to Fix It)
You're stuck in Zone 4 because your zone targets are almost certainly wrong — the 220-age formula has a ±22 bpm individual error that shifts every zone boundary by 10–15 bpm.
The Zone 3 Trap: Why Most Amateur Cyclists Lose a Full Season in the Grey Zone
Amateur cyclists spend 25–45% of training time in Zone 3 (76–90% FTP). Elites keep it under 11%. That gap explains a year of stalled fitness.
CTL Benchmarks for Ironman: What Fitness Score You Need for Your Finish Time
A sub-10-hour Ironman typically requires a race-day CTL of 120. Sub-9 hours needs 145–150. Here are the benchmarks, the ramp rate rules, and TSB taper targets by athlete tier.
Aerobic Decoupling: The Number That Tells You If Your Base Is Actually Working
Aerobic decoupling measures how much your heart rate drifts relative to pace or power. Below 5% means a race-ready aerobic base. Above 10% means your engine is leaking.
Polarized vs Pyramidal Training: The Research Has a Surprising Answer
Two 2024/2025 meta-analyses found no significant difference between polarized and pyramidal overall (SMD=-0.06). The better question is which model fits your athlete level and event distance.
VO2max Intervals: The 4x4 Rule and What Most Athletes Get Wrong
The Norwegian 4x4 protocol raised VO2max 7.2% in 8 weeks vs 1.8% for easy running. Most athletes do these sessions too often, too short, and at the wrong pace.
Zone 2 vs LT1: Why the 60–70% HRmax Definition Is Wrong
The '60–70% HRmax = Zone 2' shortcut is physiologically wrong. LT1 — your real Zone 2 ceiling — spans 69–94% HRmax across trained athletes. Here's how to find yours.
CTL, ATL, and TSB: The Mathematical Foundation of Training Load
CTL, ATL, and TSB are the three numbers that tell you whether to push harder or back off. Here's the math behind them and what they mean for your Ironman preparation.
TSS vs TRIMP: Which Training Load Metric Should You Use?
TSS uses power data; TRIMP uses heart rate. For multi-sport athletes managing three disciplines, the choice of metric determines whether your training load model is accurate or dangerously misleading.
Zone 2 Training: The Science Behind Slow Riding Making You Faster
Zone 2 is the physiological foundation of every elite endurance program. Here's the mitochondrial biology, the 80/20 data, and precise definitions that separate productive Zone 2 from glorified recovery.