How and Why the Body Responds

The body responds to any stimulus due a breakdown in the systems involved in dealing with that task. Let me give an example. When you go out in the sun, the rays do damage to your skin. The body has defense mechanisms to combat this damage. It is called melanin and is found in the skin. The more melanin your skin has, the better able to tolerate the sun's rays it is. So now say you go out in the sun and get a sunburn. This happened because the body's melanin was not sufficiently present in the skin to deal with the amount and intensity of the sun's rays you were exposed to. So, the response is to increase melanin in the skin so that next time, that same amount of sun at that intensity will not damage your skin. Hence, you get a tan. Evolutionarily, this is extremely clear in Africans and the Nordic. Africans evolved in an environment with a high degree of sun exposure at high intensities. Therefore, their skin is very rich in melanin and very dark. The Nordic people evolved in an environment far from the Equator with low volumes of sun at low intensities. Their skin evolved to be very fair. Take both of them on the first day of summer and put them in the sun. The African will deal with the sun much better than the Nordic person.

Weight training and cardiovascular training act in the same manner. Whatever is found to be the weak link in your body will be what the body aims at improving. Say you lifted weights 3 times a week and did a total body routine with 10 exercises and 4 sets per exercise. You also rest only 30 seconds in between sets. This routine is an endurance routine. Why? This routine would use a lot of intramuscular glycogen and it would require lots of oxygen in the muscles to finish this routine. So, the body would respond by increasing Type I muscle fibers (the aerobic fibers), increasing capillary density inside the muscles (to get more oxygen-rich blood in the muscles), and increasing intramuscular glycogen (to allow more stored energy). These are the systems that would be stressed greatest and broken down if the routine was done with sufficient intensity, so these are the areas of the body that would be improved.

Take a strength training routine. Why is it advantageous to do sets of less than 5 reps with high rest periods? To get maximum strength, your body uses the short term energy system, the Phosphagen system. This system uses the components creatine phosphate and ATP to work at high intensities for short periods of time. The body also uses a great deal of neuromuscular coordination to move heavy weights. So when you train using a classic strength training routine, your body adapts by increasing the phosphagen system components to let it use this energy system longer. It also gets better at how it coordinates the mind and the muscles. These factors lead to strength adaptations.

This is why using light weights and not resting long in between sets will not make you stronger although you are still lifting weights. Knowing how the body works is the key to knowing how to stress it right and get what you want out of it.