Body's adaptation to exercise

1. When we do strenuous exercise on a run, or on a bike ride, the body responds by  improving itself. So how does it happen? 
2. Exercise is considered a stress on the body. A physician named Hans Selye 1930s,  proposed "general adaptation" 
3. The theory is that the body responds to a stress in a manner intended to reduce the stress the next time we experience it.
4. When you're at rest, you're in something called homeostasis. Your heart rate and breathing rate are relatively low and constant, and there's a good match between the body's demand for energy and its capacity to supply it. 
5. Once you start exercising, the additional activity throws the body out of homeostasis and the body needs more oxygen than you're giving it. You feel out of breath, and in the short term you respond by doing things like increasing your heart rate and breathing faster to get more oxygen to your muscles. Then once the stressor is gone, once you stop exercise and returned to rest, the body works to recover from the stress. It adapts so that the next time the stressor presents itself, that is the next time you exercise, the body gets disturbed to a lesser degree. 
6. The concept is simple enough, but the adaptation or self-repair that takes place is incredibly complex. 
7. The body's response to endurance exercise involves changes in every element of the pathway that control supply and utilization of oxygen to produce energy from the brain, heart, lungs, blood vessels, and all the way to your muscles. 
8. Selye's general adaptation also applies to strength training. One key substance in muscle is protein, and at any moment two opposing protein related process that are happening in the muscle, new proteins are being synthesized, and at the same time different proteins are being broken down. 
9. Muscle atrophy happens when the rate of protein breakdown is greater than the rate of protein synthesis. 
10. Whereas hypertrophy is the opposite process, and protein synthesis is greater than protein breakdown. To increase the strength or size of your muscles, you need to boost the rate at which protein synthesis proceeds to a greater degree than protein breakdown for as long as possible. The way you do that is by stressing the muscle to stimulate the strengthening or hypertrophy of the muscle tissue. The muscle needs to experience a load that is heavy enough to fatigue the muscle. Some experiments suggest that one way to stimulate protein synthesis is to subject the muscle to a load that is greater than 60 percent of the single repetition maximum. (1RM)