ATP can be used by muscle cells very quickly, but there is only an extremely limited supply -- usually only enough for a few seconds of high intensity work. When the ATP is gone, work stops. Fortunately, the body has several ways to convert ADP back to ATP. The fastest method is to move the phosphate group off of phosphocreatine and onto ADP. This yields ATP -- which is immediately available for muscular work -- and creatine. There is enough phosphocreatine to keep ATP levels up for several more seconds.
So at this point we've moved from 2 - 3 seconds of all-out work (ATP) to almost 10 seconds (ATP + creatine). The body can recharge creatine back to phosphocreatine, but this takes time (approximately 30 - 60 seconds).
So when you say
[b said:
Quote[/b] ]But, since we arent over loading like the rest of these methods, doesn't that mean we have enough creatine?
you need to understand that we are using our ATP stores whether you are going to failure or not. Using that idea wouldn't it better to be able to stay away from metabolic failure longer and increase the loading time? Creatine helps us with this.
A variety of protocols have been used to study the effect of creatine supplementation of brief, intermittant, high intensity exercise. Some of the exercise protocols which have shown improvements in performance are listed below, with indexed references. The most common method of supplementation used a 5 or 6 day loading period, consisting of approximately 20 grams of creatine per day.
Five sets of 30 maximum voluntary knee extensions, with 60 seconds rest between sets. (1)
Ten x 6 second bouts with 30 seconds rest. High intensity work on a bicycle ergometer. Placebo controlled, double-blind study design.(2)
Bench press; 5 sets to failure (predetermined 10 rep maximum), with 2 minute rest periods. Jump squats; 5 sets of ten, with 2 minute rest periods, using 30% of each subjects predetermined 1 rep. maximum. Placebo controlled, double-blind study design. (3)
Maximum continuous jumping exercise; 45 seconds. All-out treadmill running (approx. 60 seconds), at 20 km/hr, 5 degree incline. Placebo controlled, double-blind study design. (4)
Cycling to exhaustion at 150% peak VO2 at several different protocols; non-stop (a), 60 seconds work / 120 seconds rest (b), 20 seconds work / 40 seconds rest ©, and 10 seconds work / 20 seconds rest (d). Group D showed the greatest improvement with creatine supplementation. Placebo controlled, double-blind study design. (5)
(1) Influence of oral creatine supplementation on muscle torque during repeated bouts of maximum voluntary exercise in man. Greenhaff PL, et al. Clin. Sci. 1993: 84: 565-71.
(2) Creatine supplementation and dynamic high-intensity intermittent exercise. Balsom PD, et al. Scand J Med Sci Sports. 1993: 3: 143-9.
(3) Creatine supplementation enhances muscular performance during high-intensity resistance exercise. Volek JS, et al. J Am. Diet. Assoc. 1997; 97; 765-770.
(4) Effect of oral creatine supplementation on jumping and running performance. Bosco C, et. al. Int. J. Sports Med. 1997; 18; 369-372.
(5) Creatine supplementation enhances intermittent work performance. Prevost MC, et al. Res. Quarterly Exerc. Sport. 1997; 68(3); 233-240.