What is interval training?
Interval training alternates between periods of high-intensity effort and lower-intensity recovery. This structure allows you to accumulate more time at a target intensity than a continuous effort would — producing larger adaptations in VO₂max, lactate threshold, running economy, and neuromuscular power.
The three variables — work duration, rest duration, and number of rounds — determine which energy system is stressed and what adaptation you are chasing.
Common interval training protocols
| Protocol | Work | Rest | Rounds | Ratio | Zone | Goal |
|---|---|---|---|---|---|---|
| Tabata | 20s | 10s | 8 | 2:1 | Speed/Anaerobic | Metabolic conditioning, max effort |
| Norwegian 4×4 | 4m | 3m | 4 | 1.33:1 | VO₂max | Aerobic power, cardiac output |
| VO₂max 3×3 | 3m | 3m | 5 | 1:1 | VO₂max | Aerobic capacity, running economy |
| Lactate threshold | 5m | 1m | 5 | 5:1 | Threshold | Raise sustainable race pace |
| Hill sprints | 30s | 90s | 8 | 1:3 | Anaerobic | Speed, leg power, injury resistance |
| Cruise intervals | 8m | 2m | 3 | 4:1 | Threshold/Tempo | Marathon-specific aerobic development |
Work:rest ratio guide by energy zone
The work:rest ratio is the single most important variable in interval design. It determines which energy system recovers between reps — and therefore which system is trained.
| Ratio | Zone | Work duration | Example | Key principle |
|---|---|---|---|---|
| 1:5 – 1:3 | Speed / Power | <30s | Hill sprints, strides | Full recovery required for quality |
| 1:2 | Anaerobic capacity | 30–90s | 400m reps, 600m reps | Incomplete recovery maintains lactate |
| 1:1 | VO₂max | 2–5m | 1200m reps, Norwegian 4×4 | Equal work/rest maximises VO₂ stimulus |
| 3:1 – 5:1 | Lactate threshold | 5–10m | Cruise intervals, tempo | Short rest keeps intensity just below LT |
| 6:1+ | Tempo / Aerobic | >10m | Long tempo blocks | Continuous effort, minimal rest |
Frequently asked questions
What is the difference between Tabata and HIIT?
HIIT (High-Intensity Interval Training) is a broad category covering any protocol that alternates high and low effort. Tabata is a specific HIIT protocol: 20 seconds of maximum effort followed by 10 seconds rest, repeated 8 times (4 minutes total). Dr. Izumi Tabata's 1996 study showed this specific protocol improved both anaerobic capacity and VO₂max simultaneously — making it uniquely time-efficient.
How many interval sessions should I do per week?
One to two hard interval sessions per week is optimal for most runners and athletes. The 80/20 rule of polarised training is well-supported by research: 80% of training volume at easy aerobic effort, 20% at high intensity. Adding a third hard session rarely produces extra adaptation and substantially increases injury risk and recovery time.
What does work:rest ratio mean and why does it matter?
Work:rest ratio is work duration divided by rest duration. A ratio of 1:1 means equal work and rest (e.g. 3 minutes on, 3 minutes off). A 1:3 ratio means three times more rest than work — used for speed work where full neuromuscular recovery is needed. A 5:1 ratio (more work than rest) is used for lactate threshold work where the goal is to keep intensity high with minimal breaks.