Loading…
Story
synergy · 1
Zone 2 is moderate aerobic exercise just below the first lactate threshold (LT1, also called the first ventilatory threshold, VT1), an effort at which you can still speak in full sentences. Over time it makes the muscles grow more mitochondria and a denser network of capillaries. These adaptations are not unique to Zone 2, since hard training stimulates them too, but this intensity is the easiest to do day after day and build up enough volume.
cofactor · 2
Every muscle contraction runs on ATP, and most ATP in cells has to be bound to magnesium before it can be used; the extra mitochondria and energy output that endurance training builds all depend on this step. Whether people who train endurance regularly need extra magnesium is a question the research on Zone 2 training does not answer.
Endurance training increases the mitochondrial enzymes in muscle, so at the same pace you can use more fat and less glycogen, and glycogen is exactly what runs short in the second half of a marathon. Endurance athletes who train a lot do about 80% of their training at low intensity; this describes how athletes train, and applying it to novices is an inference.
regulates · 2
Setting Zone 2 as a percentage of maximum heart rate has a problem: the 220-minus-age formula is itself off by ±10–12 beats per minute for an individual. So a simple test, being able to speak in full sentences but not sing, is often more reliable than the heart-rate number on your watch.
The lactate threshold splits training intensity in two. Below it you can pile up a lot of volume, which drives mitochondrial adaptation; the gray zone around it is thought to be a common reason amateur runners stall, because it is neither easy enough to do a lot of nor hard enough to raise the ceiling.