ATP stored in you muscles is the only fuel instantly available for energy. Stored ATP is therefore the only fuel capable of generating 100% muscle contraction. Once stored ATP is exhausted, other fuels dominate the energy supply. Because all of them must be converted to ATP before they can be used, available energy per second declines, so maximum muscle contraction declines also.

You can store enough ATP for about four-to-five seconds of maximum contraction, enough to do a l-rep max squat, throw a javelin, or run 50 meters. As 100-meter sprinters know only too well, maximum muscle contraction cannot be maintained beyond five seconds. After that the goal is to lose as little speed as possible until you pass the finish line. This exercise requires no oxygen, and not even a molecule of carbohydrate, fat, or protein, the fuels usually cited as essential for exercise.

Because it is the only way you can ever put maximum load on your muscles, muscle contraction by stored ATP is unquestionably the most effective for building strength. It creates the most extensive micro-damage, which then triggers the greatest adaptive muscle growth.

Unfortunately, it's also the most dangerous way to train, because at 100% contraction the muscle and its attachments are at greatest risk. That's why people who are constantly pushing the max--track & field athletes, powerlifters, weightlifters, and professional athletes---are always on the knife edge of muscle and connective tissue injury.

After four to five seconds of maximum exercise, creatine phosphate (CP) becomes the dominant energy control, permitting near maximum muscle contraction for another 5-6 seconds, a total of 10-11 seconds. That's enough to do a 4-rep set or sprint the 100 meters. This ATP/CP interaction is also anaerobic, and uses no glycogen, glucose, fatty acids or amino acids.

Because the ATP/CP system cannot permit maximum contraction, muscle is at less risk, so this level of exercise is much safer. Yet it still generates substantial micro-trauma, which, in turn, triggers near maximum growth. Overall, the ATP/CP 10-second window of exercise provides the best combination of safety and efficacy for optimum strength training. Now you know why creatine is so important.

As continuous maximum effort extends beyond 10-11 seconds, glycogen and glucose become the dominant fuel source. They permit sub-maximal performance for up to 120 seconds, enough to run 800 meters.

This is the aerobic/anaerobic edge. Oxygen becomes important, though strictly speaking it is not essential to the chemical reactions for use of glycogen and glucose. Some aminos and fatty acids are also pulled into the fuel mix. Even though you may make maximum effort, muscle contraction cannot stay much above 70% of maximum for this length of time. So it's a poor way to train for muscle and strength.

For exercise longer than about 120 seconds, fatty acids begin to dominate as the fuel source. Your body also pulls a lot more amino acids into the fuel mix, providing as much as 10% of the total energy. This is steady state endurance exercise, which the body can continue for many hours.

Oxygen is essential for this purely aerobic activity. It is also highly catabolic for both bodyfat and muscle. That's why you don't see muscular marathoners, and why it's not physically possible to build much strength while simultaneously training for endurance.

ATP is a simple chemical, a molecule of adenosine bonded to three molecules of phosphate. When your muscle contracts, it breaks one of these bonds causing a chemical explosion of energy. ATP is reduced to adenosine dilphosphate(ADP) and one molecule of phosphate floats free. Creatine phosphate immediatley regenerates the ATP by donating its own phosphate molecule, leaving a molecule of free creatine in the muscle. The ATP is then able to fire again.

Most of the free creatine and free phosphate molecules join together again to regenerate creatine phosphate. This process requires oxygen, so you have to stop anaerobic exercise to allow it to happen. After you stop, half the spen creatine is regenerated to creatine phosphate in about 60 seconds. A maximum of 90% is regenerated within a five-minute rest period. The rest is excreted from the muscles and appears as the waste product creatinine in your urine.

Knowing this, it is easy to figure out how long to rest between sets for maximum growth. IN order to make the most intense muscle contraction on your next set, you have to wait until the maximum amount of creatinine has regenerated---about 4-5 minutes.

Creatine phosphate is the only way to regenerate spent ADP to ATP and allow near maximum muscle contraction to continue past four to fie seconds.

Creatine occurs in many foods. Best are muscle meats of animals and fish, which contain three to six grams of creatine per kilogram, depending on the species. Your body also makes creatine in your liver, kidneys, and pancreas gland from three amino acids, the essential amino acid methionine, the conditionally essential amino acid arginine, and the non-essential amino acid glycine.

The average human body uses over two grams of creatine per day, just to maintain normal energy metabolism. That's more than twice the amount n the average diet. Your body's manufacture of creatine is also limited by the intake of the amino acid methionine, which it cannot make, and by competing calls on methionine for other tasks, such as building new proteins. For athletes the problem is compounded by the rapid use of creatine during exercise.

Recent studies show that creatine suppliments increase muscle creatine, and that strenuous execise increases muscle uptake of creatine by about another 50%. So it is likely that most athletes have sub-optimal levels of creatine in their muscles.

For short, intense exercise beyond about five seconds, extra muscle creatine should regenerate more ATP, therefore permitting more intense muscle contraction. So as soon as your muscles are loaded with creatine, you should be stronger right away.

At the Texas Southwestern Medical Center and the Cooper Clinic in Dallas, experienced weight trainers were given 20 grams of creatine per day for 28 days. They measured performance on the one-rep maximum bench press. The average increase was 18 lb, a 6.5% improvement in strength.

In another study, elite track and field athletes and body builders, using creatine cycles for periods of more than 2 years, with four eight-week cycles per year, seperated by rests of four weeks, they saw strength increases in the 1-rep maximum squat of almost 20% in a year. Because these athletes are already at the top end of the strength curve--that's enormous! A500-lb. Squat increases to 600-lbs. If you do creatine the right way, you can't miss.