Metabolic Training Zones

Metabolic training zones are intensity ranges defined by physiological thresholds measured through spiroergometry. Unlike traditional heart rate zones or perceived exertion scales, metabolic zones are based on actual fuel utilization and ventilatory responses, making them the most precise way to structure endurance training.

Zone definitions

Zone 1 (Recovery): Below first ventilatory threshold (VT1), very low RER (0.70-0.80), almost entirely fat-fueled. Zone 2 (Endurance/FatMax): Around FatMax intensity, RER 0.80-0.87, optimal fat oxidation. Zone 3 (Tempo): Between VT1 and second ventilatory threshold (VT2), RER 0.87-0.95, mixed fuel. Zone 4 (Threshold): At or near VT2, RER 0.95-1.00, predominantly carbohydrate. Zone 5 (VO2max): Above VT2, RER >1.00, maximal intensity.

Why metabolic zones beat heart rate zones

Heart rate zones are estimates based on maximum heart rate formulas, which can vary by 10-20 bpm between individuals. Metabolic zones are measured directly from your body's physiological response. Two athletes with the same max heart rate may have vastly different FatMax zones. Only metabolic testing reveals your personal thresholds and the corresponding heart rate and power values for each zone.

Applying zones to training

A well-structured endurance training plan uses metabolic zones to ensure the right stimulus. The 80/20 principle suggests 80% of training volume should be in Zones 1-2 (below VT1) and 20% in Zones 3-5. OpenSpiro maps your metabolic thresholds to heart rate and power ranges, so you can execute zone-based training with any bike computer or watch after a single test session.