Long Slow Distance (LSD)

Long slow distance is a continuous-training method emphasizing duration over intensity: covering a relatively long distance (or long time) at an easy, sustainable pace. The intensity is typically low to low-moderate — roughly the LISS/zone-2 range, comfortably below the lactate threshold — so the session can last from 45 minutes to several hours.

LSD is the classic "base training" tool in endurance sport. Its purpose is to drive the peripheral and central aerobic adaptations that come from large volumes of easy work: increased mitochondrial density and capillarization, improved fat oxidation, greater plasma volume and stroke volume, and improved fatigue resistance (see cardiac-adaptations and steady-state-vs-interval-adaptations). Because it is low intensity, weekly volume can be high without excessive recovery cost, which is why polarized endurance programs spend the large majority of their time here (see training-intensity-distribution).

LSD overlaps heavily with liss and zone-2-training; the term is most associated with running and other distance sports and connotes specifically the long end of easy continuous work.

• Long duration (≈45 min to several hours) at easy, sub-threshold intensity.
• Primary "base"/volume builder in endurance training.
• Adaptations: more mitochondria, capillaries, plasma/stroke volume; better fat oxidation and fatigue resistance.
• Forms the bulk of training time in polarized models (~80% easy).

• steady-state-continuous-training — LSD is high-volume continuous work.
• zone-2-training — the metabolic zone most LSD lives in.
• training-intensity-distribution — LSD is the "easy 80%" in polarized training.
• cardiac-adaptations — the central adaptations high volume drives.
• running — the modality the term originated with.