Training science
The endurance training science library
Plain-language explanations of the models real coaches use — training load, thresholds, periodization and recovery — each one written from the primary research and citing it. Free to read, no account needed.
41 articles
Training Models
Lactate Is Not the Enemy: LT1, LT2, and Why You Need to Go Slow
Your body produces lactate constantly, even while you are reading this sentence. At low intensities, production and clearance are balanced. LT1 (the first lactate threshold) is the intensity where lactate begins to accumulate above resting levels -- typically around 2 mmol/L. This marks the upper bo
10 min
The Norwegian Method: Double-Threshold Training
The Norwegian Method is a training system built around "double-threshold" days -- performing two moderate-to-hard threshold sessions within the same day, separated by several hours of recovery. Intensity is tightly controlled using blood lactate measurements, with the target range typically held bet
8 min
Polarized Training: The 80/20 Rule
Polarized training divides your effort into two distinct zones: easy aerobic work (Zones 1-2) comprising approximately 80% of total training time, and high-intensity intervals (Zones 4-5) making up 15-20%, while deliberately minimizing moderate "tempo" work (Zone 3) to no more than 0-5%. This approa
7 min
Pyramidal Training: The Natural Progression
Pyramidal training distributes intensity in a descending pattern: 70-80% of training time in Zone 1 (low intensity), 15-20% in Zone 2 (moderate/tempo), and 0-5% in Zone 3 (high intensity). Unlike the polarized model, which deliberately minimizes Zone 2 work, pyramidal training embraces a meaningful
7 min
Threshold Training: The Sweet Spot Approach
Threshold training is an intensity-distribution model that places a large proportion of total training time -- typically 35-55% -- at moderate intensities corresponding to Zone 3 and Zone 4 (tempo, sweet spot, and threshold efforts). This stands in contrast to polarized models (which minimize modera
7 min
Volume First? What Actually Raises Your VO2max
Because the two are answering different questions. VO2max -- the height of your aerobic ceiling -- responds fastest to intensity, because in most people the limit is how much blood the heart can pump, and hard intervals are what train the heart to pump more. Volume does something slower and structur
12 min
Load Management
Ae/An TISS: Why Identical TSS Is Not Identical Stress
TSS (Training Stress Score) is a powerful metric, but it has a blind spot: it treats all stress as equal. A kilojoule of work below threshold and a kilojoule above threshold get the same weighting in the TSS formula. AeTISS (Aerobic Training Impact Scoring System) and AnTISS (Anaerobic Training Impa
7 min
Consistency Over Peaks: Don't Pull the Carrot to See If It Grew
"Consistency over peaks" is real advice wrapped around a false dichotomy. What actually predicts success is not the shape of your training -- linear versus peaked -- but adherence: the athletes who complete their weeks win, and the ones who keep getting hurt or sick don't. Steadiness protects that a
12 min
CTL, ATL & TSB: Your Fitness Dashboard
CTL (Chronic Training Load) represents your fitness -- a rolling exponential average of your daily training stress over approximately 42 days. ATL (Acute Training Load) represents your fatigue -- a shorter exponential average over approximately 7 days. TSB (Training Stress Balance) is simply CTL min
8 min
Lactate Meters: What the Number Can and Cannot Tell You
A portable lactate meter measures something genuine, and it correlates well with laboratory analysers. What it does not have is the resolution that lactate-guided training talk implies. The device noise alone is a few tenths of a millimole; on top of that sit sampling-site differences, day-to-day bi
11 min
Normalized Power: Why Average 200W Is Not Really 200W
Average power lies to you because your body does not respond to effort in a straight line. Pushing 500 watts for 5 seconds and then coasting for 5 seconds does not feel the same as holding 250 watts for 10 seconds, even though the average is identical. Your nervous system, your cardiovascular system
6 min
Recovery Weeks: The Art of Strategic Rest
A recovery week is a planned reduction in training volume of 30-50%, typically scheduled every 3 to 4 weeks during a training block. The science behind it is straightforward: fatigue dissipates faster than fitness. When you reduce training load for 5 to 7 days, your body sheds the accumulated fatigu
7 min
The 10% Rule: Safe Volume Progression
The 10% rule states that you should not increase your weekly training volume by more than 10% from one week to the next. If you ran 30 kilometers last week, you should run no more than 33 kilometers this week. If you trained 8 hours, cap next week at 8.8 hours. The rule provides a simple guardrail a
7 min
ACWR: The Acute-to-Chronic Workload Ratio
The ACWR compares your recent training load (the last 7 days, called the "acute" load) with what your body is used to handling (the last 28 days, called the "chronic" load). When the ratio sits between 0.8 and 1.3, you are in the "sweet spot" where training stimulus is productive and injury risk is
7 min
Performance Factors
Know Your Profile -- But Train It or Just Recover By It?
An endurance athlete's profile is a genuine, measurable thing -- fiber type, the shape of your power-duration curve, your anaerobic reserve. Those variables correlate, and they are partly genetic. What the evidence does not support is the leap from "you have a profile" to "so you should train differ
12 min
Critical Power & W': Where Your Limit Actually Lives
Critical Power (CP) is the maximum power output you can sustain without progressive fatigue accumulation. Below CP, your body can clear metabolic byproducts as fast as they are produced. Above CP, a countdown begins. W' (pronounced "W-prime") is the finite energy reservoir available above CP, measur
9 min
Durability: Why Your Fresh FTP Lies About Hour Three
Durability is how well your physiology holds up as work accumulates. Every number you know about yourself -- FTP, threshold, VO2max -- was measured on fresh legs, and none of them stay put. Critical power falls by around 10% after two hours of hard riding, but the individual range runs from under 1%
12 min
FTP & Power Zones: Training by Numbers
Functional Threshold Power (FTP) is defined as the highest average power output you can sustain for approximately one hour in a quasi-steady state. It corresponds closely to the power at your lactate threshold (LT2 / maximal lactate steady state). Once you know your FTP, you can derive seven distinc
8 min
Lactate Threshold: The Best Predictor of Race Speed
Lactate threshold refers to the exercise intensity at which lactate begins to accumulate in the blood faster than the body can clear it. There are actually two important thresholds: LT1 (the aerobic threshold, around 2 mmol/L blood lactate) and LT2 (the anaerobic threshold or maximal lactate steady
8 min
Type I & Type II: Why Your Muscle Fiber Composition Determines Everything
Your muscles contain three primary fiber types, each built for a different job. Type I (slow-twitch) fibers are your endurance workhorses: packed with mitochondria, fueled primarily by fat oxidation, capable of contracting for hours without significant fatigue. Type IIa (fast oxidative) fibers sit i
8 min
Running Economy: The Hidden Performance Factor
Running economy (RE) measures the oxygen cost of running at a given submaximal speed, typically expressed as ml of O2 per kilogram of body weight per kilometer (ml/kg/km). A more economical runner uses less oxygen -- and therefore less energy -- to cover the same distance at the same pace. Among run
8 min
Why Strength Training Makes Cyclists Faster: The Science of Force for Endurance
The short version: Add heavy strength training to your riding and you start holding more power at the end of a hard effort -- not because of a bigger engine (VO2max), but because of a more efficient pedal stroke and legs that resist fatigue. In elite cyclists, 25 weeks of this work raised power in a
14 min
VO2max: Your Aerobic Ceiling
VO2max represents the maximum volume of oxygen your body can consume per minute during all-out exercise, expressed in milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). It is the single best laboratory measure of aerobic fitness. Think of it as the size of your aerobic engine:
7 min
VO2max & the Slow Component: Why Intervals Actually Work
VO2max -- your maximum rate of oxygen consumption -- is the gold standard measure of aerobic potential. It represents the absolute upper limit of your body's ability to deliver and use oxygen during exercise. But reaching that ceiling during training is harder than it sounds, and this is where the s
8 min
Periodization
Base, Build, Peak: Classic Periodization
Classic linear periodization divides your training season into distinct phases, each with a specific physiological purpose. You start with a high-volume, low-intensity Base phase (8-12 weeks) that builds your aerobic engine. You then move into a Build phase (6-8 weeks) where intensity increases and
8 min
Block Periodization: Concentrated Loading
Block periodization organizes training into short, concentrated mesocycles (blocks) of 2-4 weeks, each focused primarily on developing a single fitness quality. The foundational structure follows the Accumulation-Transmutation-Realization (A-T-R) sequence. During Accumulation, you build general aero
8 min
The Six-Week Race Block: Proven Tools, Optional Choreography
A build block is real and it works, but you should know which parts are evidence and which are tradition. Proven: short intervals beat long ones for VO2max, 4x8-minute efforts are a gold standard, concentrating hard sessions into a block outperforms spreading them out, and over-unders keep you longe
12 min
Taper: The Science of Race Readiness
Tapering is the systematic reduction of training load before competition, designed to allow the body to recover from accumulated fatigue while maintaining (or even enhancing) the fitness adaptations you have built. The research consensus is strikingly specific: reduce training volume by 40-60% over
8 min
Sport-Specific
Power vs Heart Rate: Why Watts Win on the Bike
Power meters measure the mechanical work you produce at the pedals, expressed in watts. Heart rate monitors measure how fast your heart beats in response to that work. The crucial distinction is that power is a direct measure of output, while heart rate is an indirect, delayed, and variable measure
8 min
Low-Cadence Work: Strength Builder or Just Specificity?
Low-cadence or muscle-endurance work does one thing that is real and measurable: at a given power, it makes your fast-twitch fibers do more of the work. From there the claims outrun the evidence. It does not reliably make you faster than the same session at normal cadence, it cannot replace gym stre
11 min
VDOT & Run Pacing: From Race Result to Training Zones
VDOT is a performance-adjusted measure of running fitness. It is not a direct measurement of VO2max (maximal oxygen uptake), although the two are related. Instead, VDOT accounts for both VO2max and running economy -- how efficiently you convert oxygen into forward motion. Two runners with identical
9 min
Swim CSS & Pacing: Finding Your Threshold in the Pool
Critical Swim Speed (CSS) is the swimming equivalent of Functional Threshold Power on the bike or lactate threshold pace in running. It represents the fastest pace you can theoretically sustain indefinitely without accumulating lactate beyond your body's ability to clear it. In practical terms, CSS
8 min
Special Topics
Aerobic vs Anaerobic: Two Energy Systems, One Engine
Your body uses three energy systems that operate simultaneously, not sequentially: the ATP-PCr system (immediate power for 0-15 seconds), the glycolytic system (high power for 15 seconds to 2 minutes, producing lactate), and the oxidative system (sustained power for efforts beyond 2-3 minutes, using
8 min
Beginner's Guide: Your First 12 Weeks of Training
Your first 12 weeks should follow a simple principle: build the habit before you build the engine. Start with three sessions per week on non-consecutive days, keep all training at conversational effort (Zone 1-2) for the first eight weeks, and do not introduce high-intensity intervals until week 9 a
9 min
Heat Training: A Real Adaptation With a Disputed Payoff
Heat training means deliberately raising your core temperature, either by exercising in a hot room or a heat suit, or by sitting in a sauna after training. The adaptations are well documented: plasma volume expands, heart rate at a given power drops, you sweat earlier and more, and your sweat carrie
11 min
Metabolism vs Mechanics: Why Runners Can't Just Train More
Endurance performance sits on two things: the capacity to produce energy, and the capacity of your tissues to keep absorbing the movement that produces it. Running is capped by the second one. Cycling and swimming are not, which is why their training volumes look so different. That much holds up. Wh
11 min
Nutrition Basics: Fueling Your Training
Endurance nutrition revolves around three macronutrients scaled to body weight and training load: carbohydrates (3-12 g/kg/day depending on training volume), protein (1.2-2.0 g/kg/day), and fat (minimum 0.8-1.0 g/kg/day). Pre-workout fueling means consuming 1-4 g/kg of carbohydrates 1-4 hours before
9 min
Race Day Nutrition: How Many Carbs Do You Actually Need?
For age-group triathletes the evidence-based sweet spot is 60-90 g of carbohydrate per hour, using a glucose-fructose mix, not the 100-120 g/hour numbers marketed to elites. Match intake to race duration: 0-30 g/hour for a Sprint, 30-60 g/hour for an Olympic, 60-80 g/hour for a Half Ironman, and 60-
8 min
Training After 40: Smarter, Not Slower
After age 30, VO2max declines at roughly 0.5-1.0% per year in trained athletes -- but this rate is half of what sedentary adults experience (approximately 10% per decade). Maximum heart rate drops about 1 beat per minute per year, recovery windows extend from 24-48 hours to 48-72 hours, and muscle m
8 min
Training Around Life: The Myth, the Fundamentals, and the One Real Trick
"Hard with hard" is real: concentrating intensity and then recovering genuinely works, with trials behind it. The recovery ride to "sweat out" last night's drinks is a myth -- alcohol is cleared by your liver at a fixed rate that exercise cannot touch. Rotating blocks breaks physiological plateaus,
12 min
W'bal: Your Real-Time Anaerobic Fuel Gauge
W'bal (W-prime balance) is the dynamic, real-time tracking of your remaining W' -- your anaerobic energy reservoir above Critical Power. Developed by Dr. Philip Skiba in 2012, W'bal decreases every second you ride above CP and recovers every second you ride below it. The rate of depletion is proport
7 min