One of my new hobbies was learning exercise physiology, so I read this textbook Fish had. Here's a summary of one of my favorite sections, titled Physiologic Consequences of Training.
From Aerobic (Endurance) Training:
*Mitochondria in muscles become larger and more numerous.
*Increased capacity to generate ATP, through increased enzymes & mitochondria.
*Increase in the muscles' ability to burn fat (lipid metabolism).
*Increase in the muscles' ability to oxidize carbohydrates.
*Muscle fibers get better at being muscle fibers.
*Increase in size of muscle fibers.
*Increase in heart weight and volume.
*Increase in plasma volume-->
- enhances circulatory reserve
- increases oxygen transport
- improves temperature regulation
*Decrease in resting heart rate.
*Increase in heart's stroke volume.
*Increase in maximum cardiac output.
*Increase in the quantity of oxygen extracted from blood.
*Ability to exercise at a lower cardiac output.
*Increase in cross-sectional area of arteries and veins.
*Increase in blood circulation during maximal exercise.
*Reduction in blood pressure.
*Increased breathing volumes.
*Changes in body composition, less fat, more muscle.
*Dissipate heat more economically and faster.
*You get faster.
*Psychological benefits-->
- Reduction in anxiety, stress, depression, neuroticism.
- Improvement in mood, self-esteem, self-concept.

Wow, how cool is that?

the other cool part of reading this book was coming across the studies that pointed out how fit nordic skiers were, for example:
-among olympic-caliber athletes, Nordic skiers have the highest VO2max.
-The only activities that burn more calories than "skiing, hard snow, uphill, fast" in their Energy Expenditure in Various Activities Appendix were "running, flat, 5:30 mile pace" and "Forestry, ax chopping, fast."


*I would say exercising, but I have a very difficult time spelling that word.

Mcardle, William, Frank Katch, Victor Katch. Exercise Physiology: Energy, Nutrition, and Human Performance, Fourth ed. Baltimore: Williams & Wilkins, 1996.