Durability is a 2020s-era concept that has reshaped how coaches think about long-distance performance. Traditional metrics (FTP, VO2max) describe fresh power. Durability describes power after 3+ hours of work — when races are actually won. Research on World Tour riders shows elite pros retain 95%+ of their fresh power after 3000 kJ of work; amateurs often drop 15-25%. Durability is built specifically through long rides at moderate intensity with late-ride efforts (the 'durability interval') — not through any amount of short interval work.