Your body uses three basic energy systems, and the system that your body utilizes depends on the type of training you do. If you understand how your energy systems work it may help you design a more effective exercise programme.
The first thing to point out is that no energy system works alone, but one will always dominate.
Energy comes from the food you eat (fats, proteins and carbohydrates) and the air you breath, and depending on the duration and intensity of the exercise will decide which one is engaged and which foodstuffs are broken down. However, the end result is always the same and that is the production of adenosine triphosphate (ATP). ATP is a chemical reaction within the muscle and any muscle contraction requires ATP.
The Three Energy Systems.
1) Speed System (also known as the phosphagen system)
This is the first of two anaerobic systems (without oxygen) and is employed when doing very short bursts of exercise up to about 10 seconds, such as running a 100 meters, weight training or running up a flight of stairs. There is a limited amount of ATP and creatine phosphate stored in the muscle and it is this that provides the body with that instant muscular power, hence the interest in creatine supplements. If the activity lasts longer than 10 seconds, another energy system will kick in.
2) Anaerobic System (also called glycolysis)
In sports that have long pauses between the activity, such as volleyball and racket sports, the muscle soon begins to generate energy from a second anaerobic mechanism. Sugar (glucose) is partially broken down in the muscle and to a lesser extent in the blood and elsewhere in the body into a molecule called pyruvate. This provides energy with only half the power of the speed system, but lasts longer. Its duration is limited by the chemical by-products of the sugar breakdown, lactic acid, which accumulates to high levels after about one to two minutes of strenuous play, gradually sapping all the strength out of you. Recovery from such exercises is quite slow. After about 15 minutes rest, only half of the lactic acid is flushed away and it can take over an hour to get rid of the majority of the by-product. However, you can improve the recovery time by carrying on doing moderate exercise after a strenuous exertion such as doing a victory lap or jogging back up the playing field. This system is the mainstay of most sports so it is important that you train to handle this lactic acid build up. By doing something like interval training you can build the muscles' ability to break down the sugar and enhance their tolerance of the chemical by-product.
3) Aerobic System (with oxygen)
If you are involved in long uninterrupted sports or games such as long distance running or cycling then the anaerobic systems are insufficient as an energy source. The aerobic system provides an energy-generating process that, unlike the anaerobic system, uses plentiful fuel sources, produces no exercise inhibiting chemical by-products (in fact the pyruvate molecule that was mentioned earlier participates in the formation of additional energy via aerobic processes) and can sustain energy for a long time – hours if necessary. Moving from the anaerobic system to the aerobic system can take between three to five minutes as the heart and lungs begin to deliver the extra oxygen required for aerobic reactions. Moving from anaerobic to aerobic is not always comfortable, particularly if you go to fast and intense at the beginning of a game, which can be the case in something like a football match. After the laboured breathing and crushing fatigue makes way to a smoother rhythm you then begin to feel much more comfortable. You virtually get your ‘second wind’ as your breathing and blood circulation improves. It is considered that everyone who exercises, no matter what that entails, will benefit from good aerobic conditioning.
The length and intensity of your workout will affect the goals you have set yourself. If weight loss is your goal then consider the following: Aerobic exercise is thought to be the best way to burn fat. Now this is true to a degree but there is another side to the story. Low intensity workouts use about 55% fat, 40% carbohydrates and 5% proteins as the fuel sources, however, that doesn’t mean you are burning lots of calories. To burn lots of calories at that intensity you have to work out for a long time. Higher intensity workouts may use carbohydrates as the primary fuel (70-95%) but a high intensity workout also burns fat and significantly more calories. So it's the total number of calories burned, not the fuel source, that is important. High intensity workouts will mean you will reach your goal quicker, but before you go mad on your treadmill, there's a caveat; the reason that the long low intensity workouts have been touted as the way to lose weight is because most overweight people are in poor physical condition and are just not capable of performing a high intensity workout. If they did try this route they would probably finish up being sick and full of pain and never try to exercise again. This is self defeating, so the long slow method is common sense as fat is still being burned, calories are still being used up but more importantly the participant feels comfortable and will want to do it again.
One way you can determine which energy system is engaged is by monitoring your heart. Your heart is the perfect indicator as to how hard you are working. You will be able to see by the number of heart beats the transition from anaerobic exercise to aerobic and, if the workout is intense enough, back into anaerobic. The transition point will differ from person to person and if you start to flag during a race, you may have pushed yourself into an anaerobic mode, and by looking at your heart rate you will be able to adjust your intensity to get back into the more efficient aerobic zone.
Now to mention resistance or weight training. Although fewer calories are burned during a weight lifting session, the fact you are developing muscle is a bonus. Lean muscle burns calories more efficiently than fat, even at rest, and it also has positive effects on elements such as cholesterol, glucose metabolism, and bone density.
So whatever your goal, you need to have a balanced exercise programme which utilises all three energy systems. You can of course concentrate on one more than another if your sport or activity requires it, but don’t dismiss something like weight training or interval training just because its not essential to your goal.