Creatine Monohydrate

Harris et al. further demonstrated that oral creatine supplementation improved cumulative repeated running times following 300 m and 1000 m . Individual running times for the final measured repeat run times improved as well. Final 300-m running time decreased by 0.7 second and 1000-m running time decreased by 5.5 seconds. However, one criticism of this study is that all subjects were asked to run at 90-95% of their maximal effort. Each running pace was therefore dictated by the subjective opinion of each runner. Although a threat to the study’s internal validity, these are intriguing findings because traditionally, PCr’s primary contribution to ATP maintenance takes place within approximately the first 10 seconds of intense physical exertion. Because PCr may aid ATP resynthesis for up to 3 minutes (albeit in a decreasing role with time and intensity of work) and may also act as an energy shuttle between the mitochondria and myofibrils, the efficacy of creatine as an ergogenic aid during longer anaerobic work bouts may be warranted.

In an early study, Balsom et al. investigated the effects of creatine supplementation on endurance exercise performance. Performed in a double-blind manner, habitually active to well-trained male subjects were evenly divided into treatment and placebo groups. Following 6 days of creatine supplementation, no significant differences in time to exhaustion, terrain runs, or were noted between groups and it was thus concluded that creatine supplementation clearly had no effect on endurance performance. However, other reports of anaerobic running performance suggest that creatine mayor may not improve exhaustive work bouts that last between 40 and 240 seconds.

A study by Earnest et al sought to determine if creatine supplementation would improve intermediate-length anaerobic treadmill running. In this study male subjects randomly and blindly received a creatine or glucose placebo at 20 g/day X 4 days and 10 g/day X 6 days. Following 2 weeks of rehearsal, subjects performed two exhaustive runs, separated by 8 minutes of recovery, at individually prescribed grades. Time to exhaustion for independent runs, for both runs combined, and blood lactic acid concentration were examined for each run. Significant treatment effects on group estimates of total time to exhaustion were noted. Overall, running times in the creatine group improved more during the second run , were negligible for the first run (0.5 sec), yet were significantly greater for total time to exhaustion .

In a follow-up to this investigation, Smith et al examined the effect of creatine ingestion on -

a) Time to exhaustion during intense exercise bouts used to establish the work rate-time relationship

b) The estimates of anaerobic capacity and critical power in a larger population.

Fifteen (eight male and seven female) recreationally active university students were randomly assigned and completed three phases of cycle ergometer testing, including the following -

1) familiarization-three learning trials to establish subsequent work rates

2) four baseline trials that elicited fatigue within 1 to 10 min

3) four experimental trials (post) after 5 days of either creatine or placebo ingestion given in a double-blind manner.

ANCOVA revealed a significant effect for creatine on anaerobic capacity but not critical power. Within-group time to exhaustion was also significantly different for creatine at the two highest work rates. Effect sizes for W3 and W4 were 0.86 and 0.87, respectively At work bouts of 357 and 268 watts, time to exhaustion increased from 93 seconds to 103 seconds and 236 seconds to 253 seconds , respectively. Furthermore, anaerobic capacity increased from 17.6 to 20.2 kJ .

The results of these last two studies suggest that creatine supplementation will improve shorter bouts of anaerobic work as well as longer exercise bouts lasting up to approximately 4 minutes. Although these results appear to remain consistent on a cycle ergometer, similar results obtained on the treadmill yield a conflict in the results. Creatine’s efficacy during longer anaerobic work tasks is not easily conceded in that, although improvement may be present, standardized laboratory procedures yield different results than those typically seen in practice and application. However, continued justification for this argument is provided by Jacobs et al who demonstrated that creatine ingestion increased maximally accumulated oxygen deficit (MAOD) during treadmill work bouts at 120% of max lasting approximately 120 seconds. Although most studies do show a performance benefit with creatine supplementation, several studies show no response to creatine supplementation. These results should be interpreted judiciously, however, because protocols of some studies deviated from the 5-day loading protocol shown to be effective for increasing performance. Furthermore, performance enhancement appears to be strongly related to the extent of creatine uptake into muscle with supplementation. Therefore, studies that do not measure creatine uptake by the muscle cannot rule out study participants that are nonresponders who, for one reason or another, do not absorb creatine into the muscle.