Most amateurs leave base too early. A proper base phase delivers adaptations you cannot rush — mitochondrial density, fat oxidation, aerobic enzyme concentration — and a short base leaves build work sitting on sand. Switch to build when you can hold a conversation in Zone 2 for 90+ minutes and your 30-day aerobic decoupling stays below 5%.
SIDE BY SIDE
FEATURE
BASE PHASE
BUILD PHASE
Intensity distribution
80-90% Zone 2, minimal intensity
60-70% Zone 2, 20-30% threshold + VO2max
Primary adaptation
Aerobic system, mitochondria, capillary density
Lactate clearance, FTP, VO2max ceiling
Typical duration
6-12 weeks (longer for less-trained riders)
6-8 weeks
Weekly hours (amateur)
8-15 hours (volume is the point)
6-12 hours
Fatigue accumulation
Low — recovers quickly between sessions
High — needs structured recovery
Strength training
Heavy, 2x weekly — compatible with easy aerobic
Maintenance only, usually 1x weekly
Readiness signal
Always appropriate as starting point
Aerobic decoupling <5%, effortless Zone 2 for 90+ min
CHOOSE BASE PHASE IF
✓Cyclists in the off-season (October-February for most riders)
✓Riders returning from a break or injury
✓Anyone whose easy rides don't feel easy
✓Masters cyclists for whom base work delivers disproportionate gains
CHOOSE BUILD PHASE IF
✓Cyclists 8-12 weeks out from an A-race or target event
✓Riders whose base has been solid for 2+ months
✓Returning structured athletes who already have an aerobic foundation