Cardio training types: LISS, HIIT, intervals

LISS (Low Intensity Steady State)

Continuous effort at low-to-moderate intensity (zone 2, roughly 60-70% max HR), sustained for a while (30 min or more). Example: easy jogging, a relaxed bike ride.

HIIT (High Intensity Interval Training)

Alternating short bursts of high intensity (zone 4-5) with recovery, over a shorter total time. Example: 30-second sprint / 90-second walk, repeated 8-10 times.

Intervals vs. fartlek

Interval training follows a precise, repeated structure (e.g. 6 × 400m with timed recovery); fartlek ("speed play" in Swedish) varies pace more freely and intuitively, often based on terrain.

Which one to pick?

The two complement each other rather than compete: LISS builds the aerobic base and is easy to recover from, HIIT/intervals build power and threshold. Most structured training methods combine both across the week.

Anaerobic (lactate) threshold

The intensity beyond which the body produces lactate faster than it can clear it — roughly the top of zone 3 / bottom of zone 4. Training regularly right around this threshold ("threshold training") is one of the most effective ways to push that limit and hold a faster pace for longer.

Polarised training: the 80/20 split

An approach popularised by sports science research: about 80% of training volume in zone 1-2 (easy), 20% in zone 4-5 (hard), deliberately avoiding zone 3 (the "grey zone", neither easy enough to recover well nor hard enough to progress fast).