Anaerobic Peak Power
For the absolute anaerobic PP data (W), there were no significant 2-way interactions (time × group; p = 0.209) and no main effects among groups (p = 0.989), but there were main effects for time (p < 0.001). Absolute PP increased from pre- to postsupplementation (Figures 1B and 2B) for all groups (PL, CM, PEG1.25, and PEG2.50). For the relative anaerobic PP data (W·kg−1), there were no significant two-way interaction (time ×group; p = 0.429) and no main effects among groups (p = 0.501), but there were main effects for time (p < 0.001). Relative PP increased from pre- to postsupplementation for all groups (PL, CM, PEG1.25, and PEG2.50).
Anaerobic Mean Power
For the absolute anaerobic MP data (W), there were significant 2-way interactions (time × group; p = 0.042). Absolute MP increased from pre- to postsupplementation for the CM group only (p < 0.001) but was unchanged for the PL (p = 0.265), PEG1.25 (p = 0.100), and PEG2.50 (p = 0.259) groups (Figures 1C and 2C). For the relative anaerobic MP data (W·kg−1), there were no significant 2-way interactions (time × group; p = 0.085) and no main effects among groups (p = 0.345), but there were main effects for time (p < 0.001). Relative MP increased from pre- to postsupplementation for all groups (PL, CM, PEG1.25, and PEG2.50).
For the 1RMBP data, there were significant 2-way interactions (time × group; p = 0.006). 1RMBP increased from pre- to postsupplementation for the CM (p < 0.001), PEG1.25 (p = 0.004), and PEG2.50 (p = 0.033) groups, but was unchanged for the PL (p = 0.800) group (Figures 1D and 2D). For the REPBP data, there were no significant 2-way interactions (time × group; p = 0.068), but there were main effects for time (p < 0.001). REPBP increased from pre- to postsupplementation (Figures 1E and 2E) for all groups (PL, CM, PEG1.25, and PEG2.50).
For the 1RMLP data, there were significant 2-way interactions (time × group; p = 0.029). 1RMLP increased from pre- to postsupplementation for the CM (p < 0.001), PEG1.25 (p = 0.001), and PEG2.50 (p = 0.011) groups but was unchanged for the PL (p = 0.699) group (Figures 1F and 2F). For the REPLP data, there were no significant 2-way interactions (time × group; p = 0.496), but there was a main effect for time (p < 0.001). REPLP increased from pre- to postsupplementation (Figures 1G and 2G) for all groups (PL, CM, PEG1.25, and PEG2.50).
The findings from this study demonstrated increases (p < 0.05) from pre- to postsupplementation for mean BM and anaerobic MP values for only the CM group. In addition, the mean 1RMBP and 1RMLP values increased (p < 0.05) from pre- to postsupplementation for the CM, PEG1.25, and PEG2.50 groups, but not for the PL group. Thus, all 3 forms of creatine (CM, PEG1.25, and PEG2.50) had the same effect on 1RMBP and 1RMLP strength, unlike BM and MP, where only CM demonstrated an effect. In addition, all groups (PL, CM, PEG1.25, and PEG2.50) demonstrated pre- to postsupplementation increases (p ≤ 0.05) in CVJ, PP, REPBP, and REPLP.
Several previous investigations (8,9,20,21,24) have demonstrated increases in BM after various doses and durations of CM supplementation in subjects that have different training backgrounds (8,9,20,21,24). For example, CM supplementation has resulted in increases in BM in healthy university athletes after 7 days of supplementation (21) and in American football players after 50 weeks of supplementation (28). In addition, Kelly and Jenkins (20) reported an increase in BM for experienced power lifters after 26 days of CM supplementation. Unlike the present study, however, the authors (20) used a 5-day loading period (20 g·d−1) followed by a 21-day period where the dose was reduced to 5 g. In the present investigation, there was no loading period, and the subjects were healthy, recreationally trained college men, rather than experienced power lifters. It is also important to note that in the present study, supplementation with PEG1.25 and PEG2.50 did not result in the same increase in BM, as demonstrated by the CM group (Table 1). A possible explanation for the increase in BM in the CM group is that creatine may have caused an increase in cellular volume (30). This, in turn, may have caused an increase in water retention at the cellular level that may have increased BM. The BM discrepancy between the CM and PEG groups may be a result of the smaller dose of creatine in the PEG groups (1.25 and 2.50 g) versus the CM group (5 g). Future studies should examine the effects of a larger dose of PEG creatine on BM and the subsequent influences on athletic performances that are dependent on changes in BM (e.g., running, jumping, etc).
Previous investigations have demonstrated increases in anaerobic MP during repeated Wingate tests after 5 (22), 6 (23), and 28 (8) days of CM supplementation. Unlike the present study, these previous investigations used a CM supplementation loading period that consisted of 20 g·d−1 for at least a portion of the total duration of the protocol (8,18,22,24). Similar to the present study, Earnest et al. (8) reported increases in MP after 28 days of supplementation; however, subjects were experienced in weight training, rather than healthy recreationally trained college men. In contrast, the PEG1.25 and PEG2.50 groups did not demonstrate the same increase in absolute MP as seen in the CM group in the present study. However, this interaction was not observed when the changes in BM were accounted for, because all groups (PL, CM, PEG1.25, and PEG2.50) increased from pre- to postsupplementation for the relative MP values. MP is calculated using the resistance set on the cycle ergometer multiplied by the total number of flywheel revolutions (16), and the cycle ergometer resistance is a function of BM (resistance = BM × 0.075). Therefore, increases in BM without increases in the total number of revolutions performed during the Wingate test may have accounted for our observations for absolute MP in the present study. Thus, our findings suggested that the increases in absolute MP for the CM group were BM-dependent and may not have reflected substantive improvements in power output compared with the PL, PEG1.25, and PEG2.50 groups. Therefore, similar to the improvements in CVJ, PP, REPBP, and REPLP observed for all groups (PL, CM, PEG1.25, and PEG2.50), MP may not have been influenced by the relatively small doses of creatine in the present study. Future studies should further investigate the potential dose-response nature of creatine (CM or PEG) for improving Wingate-based estimates of anaerobic power output.
Several previous investigations (23,25,26,28,29,32) have demonstrated increases in muscular strength (i.e., 1RM) after CM supplementation. In the present study, 1RMBP and 1RMLP increased for all creatine groups (CM, PEG1.25, and PEG2.50) after supplementation. A unique aspect of this study was that subjects were allowed to maintain their current exercise schedule and did not perform a structured resistance training regimen like previous investigations (3,4,19,23,26). In addition, the daily dose of creatine consumed by the PEG groups (1.25 g and 2.50 g) was considerably less than that used in previous investigations that reported similar increases (26,28,29,32) in muscular strength. For example, several studies (25,26,29) have reported increases in muscular strength after a CM supplementation period that consisted of an initial loading period of 20 g·d−1, followed by a maintenance period of 5-10 g·d−1 for the remainder of the supplementation period. Thus, the results from this study indicated that supplementation with CM (5 g) or PEG creatine (PEG1.25 and PEG2.50) may result in increases in muscular strength that are similar to those reported by studies that have used larger daily doses (5-20 g) of CM (3,4,19).
The results from the present investigation also indicated that all groups (PL, CM, PEG1.25, and PEG2.50) demonstrated significant increases in CVJ, absolute and relative PP, relative MP, REPBP, and REPLP from pre- to postsupplementation. These findings differ from those for BM, absolute MP, 1RMBP, and 1RMLP, which increased from pre- to postsupplementation for only the creatine groups. Although the exact cause for this discrepancy is unclear, it is not uncommon for CM supplementation to have different effects for different exercises (4,10). For example, Brenner et al. (4) reported that CM supplementation (20 g·d−1 for 1 week and 2 g·d−1 for 4 weeks) increased 1RMBP strength significantly when compared with a PL. However, in the same study, it was also reported that both the CM and PL resulted in significant increases in 1RM leg extension strength. In addition, Green et al. (12) reported similar increases in MP and PP after CM and PL supplementation. Furthermore, as stated previously, the subjects in the present study were allowed to continue their current exercise schedule, which could have contributed to the increase in CVJ, PP, MP, REPBP, and REPLP from pre- to postsupplementation for the PL group. Overall, our findings suggested that certain performance variables, such as vertical jump, Wingate power outputs, and REPs may be creatine dose-dependent and may require larger doses than 1.25 - 2.50 g of PEG creatine for 30 days to observe improvements. An increase in PCr concentrations from creatine supplementation is thought to enhance the ability to sustain fast ATP turnover rates (30), thereby improving performance and delaying fatigue during high-intensity exercise (3). However, the PEG-creating doses of 1.25 and 2.50 g may have not been enough of a dose to increase PCr concentrations to the extent that a dosage of 5 g of CM may have been able too. In contrast, 1RM strength measurements may be improved by relatively small doses of creatine used in the present study. However, it has also been suggested that resistance training exercise can improve creatine uptake (14). Therefore, future investigations should examine the effects of small-dose CM and PEG creatine on performance after a period of supplementation combined with resistance training.
The observed safe limit (OSL) has been proposed by Shao and Hathcock (27) as a guideline for the amount of creatine that can be safely consumed throughout a long-term supplementation period. Shao and Hathcock (27) have recommended that, based on the findings of Derave et al. (7), the OSL for creatine should be 5 g·d−1. The present investigation's supplementation doses were equal to (CM) or less than (PEG1.25 and PEG2.50) the suggested OSL and, therefore, demonstrated that increases in 1RM performance can be achieved when adhering to Shao and Hathcock's (27) OSL recommendations. However, a limitation of the present investigation is that the increases in CVJ, PP, MP, REPLP, and REPBP for the creatine groups (CM, PEG1.25, and PEG2.50) were not significantly greater than those for the PL group. Thus, it is possible that larger doses of creatine may have been required to result in significant improvements in these performance measures when compared with the PL group.
In summary, the results from this study showed that CM supplementation resulted in increases in BM and absolute MP that were significantly greater than those for the PL, PEG1.25, and PEG2.50 groups. However, for relative MP, all groups (PL, CM, PEG1.25, and PEG2.50) improved over time. In addition, CM, PEG1.25 and PEG2.50 supplementation resulted in increases in 1RMBP and 1RMLP that were significantly greater than those for the PL group. These results supported those from previous investigations (3,4,19,23,26,28,29,32) that have examined the effects of creatine on BM and 1RM strength. However, our findings did not support previous studies that have observed creatine-induced improvements in muscular power (15,18,22,24) and repetitions to exhaustion (17,31). Furthermore, these findings are important from a practical standpoint because they indicated that PEG creatine may result in similar increases in strength when compared with CM but with a dose reduction of as much as 75%. It is important to note, however, that there were increases from pre- to postsupplementation for CVJ, PP, relative MP, REPBP, and REPLP for all groups (PL, CM, PEG1.25 and PEG2.50). Thus, additional studies are required to determine if PEG creatine supplementation has ergogenic effects that are comparable to those of CM. Future investigations should also examine the potential ergogenic effects of PEG creatine combined with a strength/power training program.
One of the unique aspects of the present investigation was that CM and PEG creatine supplementation improved 1RM strength without the use of a loading period. In addition, the daily doses of creatine consumed by the PEG creatine groups (1.25 g and 2.50 g) were considerably less than those used in many previous investigations (3,4,19,23,25,26,29) but still resulted in increases in 1RMBP and 1RMLP that were the same as those for a 5-g dose of CM. Thus, the use of PEG creatine may result in improvements in strength that are comparable to those with the OSL dose for CM (5 g·d−1) recently proposed by Shao and Hathcock (27). More research is required, however, to examine the effects of PEG creatine combined with training.
This study was funded by a research grant from the General Nutrition Corporation (Pittsburgh, Pa.).
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Keywords:© 2009 National Strength and Conditioning Association
wingate test; countermovement vertical jump; bench press; leg press