90-120 minutes of running at constant effort (Z2, guided by pace or power) with heart rate monitoring every 30 minutes. Measures aerobic 'durability': resistance to degradation of physiological responses over time.
Total 2h05
Foundational endurance training stimulates mitochondrial biogenesis and capillary network development around type I muscle fibers. By maintaining a low intensity (below the first ventilatory threshold), the body optimizes fatty acid oxidation as an energy substrate, sparing muscle and hepatic glycogen for higher-intensity efforts.
Z1 promotes active recovery and increases blood flow to muscles without generating significant fatigue, allowing for high training volume.
Z2 is the optimal intensity to maximize fat oxidation and stimulate mitochondrial proliferation. It is the core of polarized training, representing 75-80% of total volume.