Zone 2: balancing training volume against metabolic fatigue

The obsession with accumulating Zone 2 mileage obscures a fundamental tension: training volume and metabolic fatigue are not natural allies but competitors requiring careful arbitration. Peter Attia examines how endurance athletes conflate quantity with adaptation, when true gains in aerobic capacity depend on keeping fatigue within specific thresholds that permit recovery and neuromuscular improvement. This distinction is not academic—Zone 2 work above certain fatigue limits generates performance plateaus and even regression. The practical implication is direct: the relevant question for someone aging with health is not "How many Zone 2 kilometers am I logging?" but "What's the maximum volume I can sustain without compromising recovery and my capacity for higher-intensity work?" This reframe transforms Zone 2 from a quantity metric into a tool of metabolic intelligence.