Additionally, attention to posture allows one to reduce undue stress in parts of the body which are not specifically in use. For example, removing unnecessary tension from the upper body allows more energy to be diverted to the lower body. This is the most biomechanical sport of all, so posture is key to properly harnessing the necessary muscles, avoiding cramps and tightness, and staying fluid and smooth on the bike. Proper posture is also critical for aerodynamic slipperiness. Posture is critical, of course, to safe strength training, but is also useful for developing subtle variations on different movements in order to tweak the most gains from the workout.
Posture can also improve traction and footing, and help one to minimize overall fatigue.
Heartrate Heartrate is the body's barometer to indicate the totality of the athletic experience. This is the one pillar which is most quantifiablly affected by working with the other six pillars, because heartrate is expressed as a number. By becoming familiar with my heart, I discovered heartrates that I could maintain for given amounts of time with, effectively, little or no overall cost. Then I would achieve that heartrate goal by working with the other six pillars, thus becoming truly efficient, almost a perpetual motion machine. Intensity Intensity is what you're working against, what your effort is actually directed towards.