A ride in power zones 2 and 3 will meet your low-intensity cardio needs, even if your heart rate starts in zone 1 and spikes into zone 3 by the end. For other forms of cardio, go by feel ...

Attia claims that “Zone 2” training ... in Zone 1, his thinking goes, your mitochondria won’t be working hard enough to spur significant improvements. If you ramp up to Zone 3, the point ...