Most runners know intervals work. Few know which ones to use, when to use them, or why one session produces different results than another. This library covers every major session type used in structured endurance training: VO2Max intervals, track sessions, threshold work, and fartlek. Each entry includes the structure, the training zone, the physiological effect, and who it is best for.
Each session in this library shows the structure, training zone, primary physiological effect, and who it is best for. Use it as a reference when building or adjusting your training block. Do not try to include all sessions. Pick one per category per block and run it consistently.
Intervals are a tool for a specific physiological adaptation at a specific stage of training. Used in the right order, with the right base behind them, they drive real progress. Used too early or without structure, they create fatigue and stall progress. The sequence matters.
| Session type | Enters training at |
|---|---|
| Fartlek | After 2–3 weeks of Zone 2 base |
| Threshold | Week 4–6 (after base phase) |
| Track intervals | Week 5–7 (after threshold) |
| VO2Max intervals | Week 6–8 (after threshold) |
Adding intervals does not mean training hard every day. 80% of your weekly volume should remain in Zone 1–2. The sessions in this library cover the 20%. One quality session per week is enough for most runners. Two is advanced.
22 sessions · 4 categories
VO2Max Intervals
The Norwegian Method
Primary effect
Raises aerobic ceiling. Increases maximal oxygen uptake. The highest-quality aerobic stimulus available.
Best for
Trained runners with 6+ weeks of base and threshold work behind them.
All reps should feel equal. If pace drops on rep 3–4, reduce intensity next session.
Short VO2Max
Primary effect
High aerobic stimulus with shorter individual efforts. A good entry point into VO2Max work.
Best for
Runners transitioning from threshold work to VO2Max for the first time.
Slightly easier to control pace per rep than longer intervals.
High-rep VO2Max
Primary effect
Accumulates VO2Max stimulus via volume of reps. Less demanding per rep, more total quality work.
Best for
Runners who struggle to pace longer intervals or returning from a break.
Long VO2Max
Primary effect
Maximises time at VO2Max per session. Demands high aerobic capacity and pacing discipline.
Best for
Experienced runners with strong base. Not suitable for a first VO2Max block.
Start conservatively. Rep 1 should feel almost too easy.
High-volume short reps
Primary effect
High total VO2Max stimulus via rep volume. Develops repeatability at near-max effort.
Best for
Runners with solid VO2Max base who want to increase session volume without longer reps.
Short recovery keeps intensity honest. Do not sprint. Control the effort.
Extended VO2Max
Primary effect
Longest VO2Max stimulus per rep. Builds aerobic power at near-maximum for extended periods.
Best for
Half marathon and marathon runners. Advanced session. Strong base and threshold required.
Pacing is critical. A runner who blows up at rep 3 went too hard on rep 1.
Track Intervals
Speed endurance
Primary effect
Speed endurance and race pace sharpness. Slightly lower volume than 10×400 with similar stimulus.
Best for
Mid-distance runners preparing for 5K–10K races.
Classic track session
Primary effect
Builds speed endurance and lactate tolerance. Develops pace awareness at race effort.
Best for
5K and 10K runners. Strong aerobic base required.
First rep should feel controlled. Last rep should feel like you could not do an 11th.
Longer track reps
Primary effect
Race pace development and lactate tolerance. High total quality load.
Best for
10K runners. Requires solid threshold base.
Pace should be consistent across all reps, not a progression.
Kilometre reps
Primary effect
Develops lactate threshold and race pace tolerance over longer efforts.
Best for
10K and half marathon runners. Good bridge between threshold and VO2Max work.
Speed development
Primary effect
Develops raw speed and neuromuscular efficiency. Short enough to maintain form across all reps.
Best for
5K runners and runners who lack top-end speed. Good late-block sharpener.
Not a sprint session. Run at controlled speed, not all-out.
Mile reps
Primary effect
Develops sustained race pace over long efforts. High total threshold and VO2Max stimulus.
Best for
Half marathon and marathon runners. Advanced track session.
Demanding. Only enter this session after 6+ weeks of structured quality work.
Threshold Sessions
Continuous threshold
Primary effect
Raises lactate threshold. Makes sustainable race pace faster. The most direct threshold stimulus.
Best for
Experienced runners who can hold pace without drifting into Zone 5.
Threshold pace = fastest pace sustainable for 45–60 min in a race. Short sentences, not paragraphs.
Cruise intervals
Primary effect
Same threshold stimulus as continuous tempo but with built-in recovery. Easier to maintain quality.
Best for
Runners new to threshold work or returning after a break.
Longer cruise intervals
Primary effect
Extends time at threshold per rep. Higher quality demand than 4×8. Good progression from shorter reps.
Best for
Runners who have completed 3–4 weeks of cruise intervals and want to progress.
Long broken tempo
Primary effect
High threshold volume per session. Bridges cruise intervals and continuous tempo.
Best for
Runners in weeks 5–7 of a structured block. Good step up from 3×10.
If pace drops on rep 2, the recovery was too short or intensity too high.
Build into threshold
Primary effect
Develops the ability to finish hard after easy miles. Mirrors race conditions.
Best for
Weeks where full tempo feels too demanding. Good option mid-block.
Lactate fluctuation
Primary effect
Teaches the body to clear lactate during low-intensity recovery. Develops lactate tolerance.
Best for
Advanced runners preparing for half marathon or marathon. Demanding session.
Common in Norwegian training blocks. Not suitable for a first threshold phase.
Fartlek
Speed play
Primary effect
Develops speed and aerobic capacity in an unstructured format. Low psychological demand.
Best for
Runners transitioning from pure base work to structured intensity.
No GPS pacing required. Run by feel. Hard should feel hard, easy should feel easy.
Aerobic fartlek
Primary effect
Higher total quality volume than 30/30. Builds VO2Max stimulus without rigid structure.
Best for
Runners who respond poorly to highly structured sessions. Flexible option.
Progressive effort
Primary effect
Varied effort duration develops both speed endurance and VO2Max stimulus in one session.
Best for
Runners who find standard interval sessions mentally repetitive. Good mid-block session.
Total quality time: 16 min. Feels like more. A good introduction to longer efforts.
Strength and power
Primary effect
Builds running-specific leg strength and aerobic power. Lower injury risk than flat speed work.
Best for
Runners who want VO2Max stimulus with added strength development. All levels.
The downhill jog is the recovery. Do not rush it.
The most common mistake is doing too much. Runners see a library of intervals and want to include all of them. One quality session per week, layered onto consistent Zone 2 work and a weekly long run, is what drives adaptation. Pick one session per block. Run it consistently for 4–6 weeks. Test. Adjust. Repeat.
| Day | Session | Zone |
|---|---|---|
| Monday | Rest or easy walk | |
| Tuesday | Easy run 40–55 min | Zone 2 |
| Wednesday | Quality session (from this library) | Zone 4–5 |
| Thursday | Rest | |
| Friday | Easy run 40–55 min | Zone 2 |
| Saturday | Long run 75–90 min | Zone 2 |
| Sunday | Rest |
One long run per week. Never skip it.
One quality session per week. Two is advanced.
One interval type per block. Consistency beats variety.
One test every 6–8 weeks. Close the loop.
The full picture
Intervals are step 3 and 4 of 5. The ebook covers all five steps in the correct sequence: zone calibration, base building, threshold work, VO2Max training, and progress testing. Everything in order. Nothing skipped.
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