LIT is the majority of training time for virtually every elite endurance athlete. Polarised training dedicates ~80% of training time to LIT, which drives mitochondrial biogenesis, capillarisation, and fat oxidation — adaptations high-intensity work can't produce. The single biggest mistake in amateur cycling: riding LIT sessions too hard. 'Easy' should be genuinely easy, usually at 60-75% of FTP and below aerobic threshold. Heart rate is the best real-time guide because power meters mask internal physiological load on easy days.