Which Comes First, Cardio or Weights_ - Alex Hutchinson [1]
No matter what type of exercise you choose, there are some basic concepts that govern the training process, in particular, the “Specific Adaptation to Imposed Demands” (SAID) principle:
When the body is subjected to stresses and overloads of varying intensities, it will gradually adapt over time to overcome whatever demands are placed on it.
That’s what every form of exercise boils down to. The stress could be lifting weights or pedaling a bicycle, and the adaptation is bigger muscle fibers, a stronger heart, and hundreds of other microscopic changes. The key is balancing the size of the stress: too small (lifting a half-pound weight, say), and your body won’t see any need to adapt; too large, and it won’t have a chance to adapt due to injury or exhaustion. Much of the research described in this book aims to help you find this delicate balance.
Your body’s overall goal in making these adaptations is, simply put, to more efficiently convert the energy from your food into physical action. Every move you make is powered by the contraction of muscle fibers, and these contractions are fueled by a molecule called ATP (adenosine triphosphate) extracted from the carbohydrate, fat, and protein you’ve eaten.
Your body has several different ways of converting nutrients to ATP. One supply is stored in a form called phosphocreatine, which can provide energy for short, intense bursts lasting up to about 10 seconds. A process called glycolysis offers another source of ATP that lasts about 45 seconds. Neither of these processes requires oxygen to create ATP, so they’re known as “anaerobic” (literally “without oxygen”) energy sources. For longer spurts of exercise, the tiny “power plants” in your cells called mitochondria can convert carbohydrate or fat to ATP, but the process requires oxygen—which is why sustained exercise is referred to as “aerobic.”
As your body adapts to exercise, you’ll become more efficient at every step of this process. Your cells generate more mitochondria, enabling you to produce more ATP; you start burning a higher proportion of fat (a virtually unlimited form of stored energy) instead of carbohydrate; and the muscle fibers themselves produce more force with each contraction.
In addition to these functional adaptations, your body will remodel its structure. Less fat and bigger muscles are the two most obvious changes, but other adjustments will be taking place under the surface. The constant tug of stronger muscles on your skeleton results in stronger bones; your heart literally grows bigger in order to pump more oxygen-rich blood to hard-working muscles; you develop a more extensive network of capillaries to distribute that blood; the nerves that carry commands from your brain to your muscles learn to do so more quickly and efficiently; and on and on.
In some ways, though, the most important adaptations—and perhaps the most unexpected—are those that occur in the brain. This is a field of research that remains in its infancy, though it has been gathering momentum for the past few years. But what we do know for sure is that the increased flow of blood and growth factors to the brain during exercise has dramatic effects, boosting memory and learning, enhancing cognition, and warding off the effects of aging. And exercise also stimulates the release of powerful mood-altering chemicals like endorphins, so much so that some researchers argue that it can become a mild addiction.
If that’s the case, it’s an outcome that I devoutly wish for everyone who reads this book. When, as a teenager, I started trying to run on a daily basis, it was a tremendous chore. It stayed that way for several years—until, during a layoff due to injury, I suddenly realized how much I missed it. These days, my workout is the highlight of my day, a chance to get outside, unwind, perhaps spend time with my wife or friends, or simply be alone with my thoughts.