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Effect of Thirty Days of Creatine Supplementation with Phosphate Salts on Anaerobic Working Capacity and Body Weight in Men

Eckerson, Joan M; Bull, Anthony A; Moore, Geri A

Journal of Strength and Conditioning Research: May 2008 - Volume 22 - Issue 3 - p 826-832
doi: 10.1519/JSC.0b013e31816a40ad
Original Research
Free

The purpose of this study was to determine the effect of 30 days of single-dose creatine supplementation with phosphate salts (CPS) on body weight (BW) and anaerobic working capacity (AWC) in men. Using a double-blind design, 32 men randomly received 1 serving of either CPS (5 g Cr + 4 g phosphate) (n = 17) or 20 g of dextrose as placebo (PL) (n = 15) for 30 days. AWC determined from the Critical Power Test and BW were measured at baseline, 10 days, 20 days, 30 days, and 10 days post-supplementation. Results (2 × 5 ANOVA) showed no significant differences between groups for AWC at any time point; however, BW was significantly increased at 10 days in the CPS group (1.0 kg) vs. PL (0.0 kg), and remained elevated for the duration of the study. These findings suggest that a single 5 g·d−1 dose of CPS for 30 days increases BW but is not effective for increasing AWC in men.

Department of Exercise Science, Creighton University, Omaha, Nebraska

Address correspondence to Dr. Joan M. Eckerson, eckerson@creighton.edu.

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Introduction

Many athletes involved in sports that require bouts of high-intensity exercise ingest supplements containing creatine (Cr) to enhance anaerobic performance. Accordingly, in the last several years, a large number of studies have been conducted to examine the safety and effectiveness of Cr supplementation using various subject populations. Although not all studies have shown an ergogenic benefit, there is a preponderance of evidence to suggest that Cr supplementation is effective for improving athletic performance in activities that primarily rely on the anaerobic energy systems. The performance-enhancing effects of Cr have been attributed to several factors, including improved Cr phosphate (CrP) resynthesis, increased buffering capacity, and greater shuttling of mitochondrial ATP into the cytoplasm (11,14).

The dosing strategy used in most Cr studies includes a loading phase of 20-25 g·d−1 or 0.3 g·kg·BW−1 for 5-7 days, followed by a maintenance phase of 2-5 g·d−1 or 0.03 g·kg·BW−1 for several weeks to maximize Cr uptake into the muscle (2,3,5,14,16, 19,20,27,30,35,38,39,41). Increases in intramuscular stores of total Cr (TCr) and CrP as a result of loading are typically reported to range from 9.5%-32.0% (1,7,11,14,22,26,30, 38) and 6.0%-25.0% (1,7,14,22,30,38,39), respectively. These dosing strategies have also been shown to enhance anaerobic working capacity (AWC) (8,9,33), cycling performance (20,40), and muscular strength (2,3,5,16,19,27,35,39,41).

Another dosing strategy that has been shown to be as effective as a loading protocol for increasing muscle TCr (∼20%) is the ingestion of a single dose of Cr (3 g·d−1) for 28 days (14). However, this regimen may not be as effective as Cr loading for improving anaerobic exercise performance. For example, Thompson et al. (37) reported that 2 g·d−1 of Cr for 6 weeks had no significant effects on muscle TCr concentration (via 31P magnetic resonance) or 100- and 400-m performance time compared with PL in female college swimmers. In agreement, Wilder et al. (42,43) also reported that 10 weeks of low-dose Cr administration (3 g·d−1) in combination with a periodized resistance training program had no significant effects on strength, percent body fat (%BF), and fat-free weight (FFW) versus training alone in NCAA Division I football players.

In contrast to these studies (37,42,43), Burke et al. (6) reported that 21 days of Cr supplementation using a dose equal to 0.03 g·kg·BW−1 (∼ 7.7 g·d−1) resulted in significant increases in force, power, and total work compared with PL in college-age males who were also concurrently participating in a resistance training program. The dose used in the study by Burke et al. (6) was 5-6 g·d−1 higher than that used in the studies by Wilder (42,43) and Thompson (37), which may account for some of the differences in the findings.

Other studies that used a single serving of Cr at relatively low doses, but for shorter periods of time than the studies described above, have also reported conflicting findings. Hoffman et al. (12) recently conducted a study to determine the efficacy of low-dose, short-duration Cr supplementation and reported that 6 g·d−1 for 6 days had no effect versus PL on BW, peak power, mean power, or total work derived from three, 15-s Wingate anaerobic power tests in 40 physically active college-age men.

In contrast, Magnaris and Maughen (21) found that a Cr dosage of 10 g·d−1 for 5 days increased BW (1.7-1.8 kg) and significantly improved the isometric endurance capacity and maximal voluntary contraction of the leg extensors in healthy men when compared with PL. Similarly, Rossouw et al. (31) reported that 9 g·d−1 for 6 days resulted in significant increases in dead lift volume and maximal intermittent isokinetic exercise performance in experienced power lifters.

Although there is a plethora of research that has shown that Cr loading (20-25 g·d−1) for 5-7 days is effective for increasing muscle TCr and enhancing anaerobic exercise performance, the timing and dosage necessary to slowly load the muscle with Cr is less clear. Based upon the results of the majority of studies mentioned above, it appears that supplementation with lower doses (<10 g·d−1) of Cr should occur for more than 6 days and be greater than 3 g·d−1 to elicit significant increases in performance. To gain a better understanding of how lower doses of Cr administration affect performance, and perhaps determine a “threshold” dose for slowly loading the muscle over time, the purpose of the present study was to examine the effect of a “typical” maintenance dose of 5 g·d−1 of Cr + phosphate salts (CPS) for 30 days on AWC and BW in physically active men.

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Methods

Experimental Approach to the Problem

The number of studies that have examined the effect of lower doses of Cr to more slowly load the muscle and determine its efficacy for enhancing anaerobic exercise performance is limited, and the studies have resulted in conflicting findings. Therefore, we examined the effect of 30 days of CPS supplementation on BW and AWC in men using a dose that is more commonly associated with a maintenance phase. Using a double-blind design, 32 men randomly received 5 g·d−1 of CPS with 18 g of dextrose (n = 17) or 20 g of dextrose as PL (n = 15) for 30 days. Body weight and AWC determined from the Critical Power Test were measured at baseline, 10 days, 20 days, 30 days, and 10 days post-supplementation. Differences between BW and AWC were determined using separate 2 × 5 (group × time) mixed factorial analysis of variance (ANOVA), followed by appropriate contrast tests when a significant F ratio (p < 0.05) was observed.

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Subjects

Thirty-two men ( age ± SD = 21 ± 2 yr; range = 18-26 years) volunteered to serve as subjects for this investigation. The subjects were physically active and participated in aerobic exercise and/or resistance training exercise for at least 60 minutes 4 times weekly. Body composition via skinfolds was determined prior to testing, and individuals who were ≥20% fat were excluded from participation. None of the subjects had ingested Cr, or any other dietary supplements, for a minimum of 12 weeks prior to the initiation of the study, nor were they taking medications that would affect the outcome of the study. The investigation was approved by the Institutional Review Board and informed written consent was obtained from each subject prior to the initiation of the study.

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Supplementation Protocol

Following baseline (BL) testing, the subjects were randomly assigned to 1 of 2 treatment conditions using a double-blind design: (A) 20 g of flavored dextrose powder as a PL (n = 15); or (B) 5.0 g of Cr citrate + 2 g of monobasic sodium phosphate + 2 g monobasic potassium phosphate and 18 g of dextrose (CPS) (n = 17) (Mega Creatine™, General Nutrition Center, Inc., Pittsburgh, PA). The powders were packaged to be identical in taste and appearance and were dissolved in 16 oz. of water and ingested once per day for 30 consecutive days. During the course of the study, the subjects were asked to maintain their normal dietary and activity patterns and abstain from other nutritional supplements and nonprescription drugs. In addition, the subjects were instructed to refrain from exhaustive physical exercise, as well as caffeine and alcohol consumption, for 24 hours prior to testing. The subjects were questioned upon each visit to the laboratory and testing was rescheduled for the following day if they were noncompliant with the above criteria.

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Critical Power Test

The subjects completed 4 phases of testing on a calibrated electronically braked cycle ergometer (Corival 400, Quinton Instruments, Seattle, WA): (A) a Critical Power Test familiarization trial to establish power outputs for subsequent testing; (B) BL testing, consisting of 2 bouts of cycling exercise performed at power outputs selected to elicit fatigue within 1-10 minutes; (C) posttesting following 10 days, 20 days, and 30 days of supplementation at power outputs identical to those performed during BL testing; and (D) testing 7-10 days postsupplementation at the same power outputs used during BL and post-testing.

The procedure for the Critical Power Test has been previously described by Housh et al. (13). Prior to each exercise bout, the seat height of the cycle ergometer was adjusted for near full extension of the subjects' legs while pedaling, and toe clips with straps were secured to prevent the feet from slipping off the pedals during testing. The subjects warmed up for 5 minutes at a power output of 50-70 Watts. Once the subject was warmed up and reached a pedaling rate of 70 rev·min−1, the appropriate power output was applied within the first 2-3 seconds of the test. If the rev·min−1 fell below 70, verbal encouragement was used to help motivate the subject to return to 70 rev·min−1. The exercise bout was immediately terminated when the subject could no longer maintain 65 rev·min−1 as determined by the monitor on the cycle ergometer. Heart rate and blood pressure were measured prior to the first and second bout of exercise. The 2 exercise bouts were completed on the same day and the subjects rested between each bout until their heart rate and blood pressure returned to within 10 b·min−1 and 20 mm Hg, respectively, of pre-exercise levels, which typically took 15 minutes or longer.

Time limit (TL) was recorded to the nearest 0.1 second and work limit (WL) was calculated by multiplying the power output (P) by the TL (WL = P × TL). The AWC represented the amount of work in kilojoules (kJ) corresponding to the y-intercept of the WL-TL relationship as previously described (24,25). Test-retest reliability data for AWC from the authors' laboratory for young men (n = 11) measured 7 days apart resulted in an intraclass correlation of 0.97 with a standard error of the mean of 0.59 kJ.

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Body Weight and Body Composition

Body weight was measured to the nearest 0.11 kg using a calibrated physician's scale prior to Critical Power testing at BL, 10 days, 20 days, 30 days, and 10 days post-supplementation. Before the familiarization trial and at 30 days post-supplementation, body composition was determined using the sum of 3 skinfolds equation of Jackson and Pollock (15). Skinfold measurements were taken on the right side of the body using Lange calipers at the chest, abdomen, and thigh by an investigator who had previously shown test-retest reliability of r > 0.90. Body density values were converted to percent fat using the Siri (32) equation and any subject who was ≥20% fat at familiarization was excluded from the study. The mean values for percent body fat for all subjects prior to and following 30 days of supplementation are presented in Table 1, and the mean values for each of the two groups are presented in Table 2.

TABLE 1

TABLE 1

TABLE 2

TABLE 2

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Statistical Analyses

Differences between BW and AWC were determined using separate 2 × 5 (group × time) mixed factorial ANOVA, followed by appropriate contrast tests when a significant F ratio (p ≤ 0.05) was observed.

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Results

The descriptive characteristics of the subjects are provided in Table 1. All subjects included in the analyses had consumed ≥80% of their respective supplement (i.e., a minimum of 24 packets). Slight differences in the “n” for each variable in the tables were the result of some subjects who did not complete testing at 10 days, 20 days, 30 days, or 10 days post-supplementation as a result of scheduling conflicts for testing or voluntary withdrawal from the study.

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Body Weight

The results for BW indicated that there was a significant time × group interaction (p = 0.018) and significant time effect (p = 0.001). When examining the time × group interaction, contrast tests indicated that only the CPS group experienced a significant increase in BW. Body weight at 10 days (78.9 ± 5.1 kg), 20 days (79.1 ± 5.1 kg), 30 days (78.9 ± 5.2 kg), and 10 days post-supplementation (78.5 ± 4.4 kg) was significantly greater compared with BL (77.9 ± 5.1 kg) (Table 2).

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Anaerobic Working Capacity

The results of the 2 × 5 ANOVA for AWC indicated that there was no time × group interaction (p = 0.438) (Table 2). In addition, there were no significant main effects for time (p = 0.226) or group (p = 0.149) (Table 1). The increase in AWC from BL to 30 days for the CPS and PL group was 4.2% and 1.7%, respectively. A comparison of the effect sizes indicated that CPS was moderately effective (Cohen's d = 0.41), whereas the PL was ineffective (d = 0.16).

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Discussion

The typical Cr dosing strategy involves a high dose loading phase of 20-25 g·d−1 for 5-7 days followed by a low dose maintenance phase of 2-5 g·d−1 (4,23) for 3 -10 weeks, and a considerable number of studies that have used this dosing protocol have reported significant improvements in anaerobic exercise performance and FFW (2,3,5,14,16,19, 20,27,30,35,38,39,41). Other studies (17,18) that used high Cr doses (16 to 22 g·d−1) for 4-6 weeks without a maintenance phase have also reported significant increases in FFW (17,18), vertical jump (17), isotonic lifting volume (18), and sprint performance during training (17,18), without any adverse health effects.

Although a majority of Cr studies report using a high-dose loading phase for at least 5 days, Harris et al. (11) found that Cr uptake into muscle is greatest during the first 2 days of loading (6 × 5 g·d−1 × 7 d), with approximately 20% of the Cr taken up as CrP. Therefore, high doses of Cr for more than 2 days may actually be unwarranted to improve exercise performance, and the results of a few studies that either examined the effect of a 2-3 day loading phase alone (9,40,44), or with a maintenance dose thereafter (29), appear to support this finding.

Another dosing strategy that has scientific basis is to slowly load the muscle with Cr using low doses for longer periods of time. Hultman et al. (14) have reported that a single Cr dose of 3 g·d−1 for 28 days was sufficient to gradually increase muscle TCr concentrations by 20%, which corresponds to the increases typically observed with loading. Although the findings of the current study showed that a single 5 g·d−1 serving of CPS for 30 days resulted in a significant increase in BW when compared with PL, there was no statistically significant effect on AWC. For the CPS group, BW was significantly increased at 10 days (1.0 kg), and remained elevated throughout the duration of the study, whereas the PL group experienced no significant changes in BW at any time point (Table 2). The finding of no significant differences in AWC in the current study could be attributed, in part, to the exclusion of a loading dose, since other studies which have examined the effects of both long-term and short-term low-dose Cr supplementation without a loading phase have also reported nonsignificant findings (12,37,42,43).

In a study by Thompson et al. (37), the effect of low-dose Cr supplementation on skeletal muscle TCr concentration and performance time was examined in 10 female college-athlete swimmers. The women randomly received either 2 g·d−1 of Cr (Ergomax® tablets; AMS Ltd., Goole, North Humberside, UK) or a PL for 6 weeks. The results following supplementation showed that low-dose Cr supplementation had no significant effects on muscle TCr concentration (via 31P magnetic resonance) or 100- and 400-m performance times compared with PL.

In a related study, Wilder et al. (42) compared the effect of 10 weeks' low-dose Cr administration (Createam Chewables; NutraSense Co., Shawnee Mission, KS) (n = 8; 3 g·d−1) and Cr loading (n = 8; 20 g·d−1 × 7 d followed by 5 g·d−1) on strength (1 RM back squat), percent body fat (via underwater weighing), and FFW versus PL (n = 9) in 25 highly trained NCAA Division I football players during their off-season strength and conditioning program. There were no significant interactions for strength or percent body fat among the groups following supplementation. However, there were significant time effects for all 3 groups for 1 RM squat and FFW, indicating that the training program alone was primarily responsible for the observed increases in strength and lean mass. Although the strength differences between the 3 groups were not statistically significant, it is worthy to note from a practical standpoint that the low-dose group demonstrated the greatest change in 1 RM values (19.0 kg) when compared with both the loading (8.8 kg) and PL (8.9 kg) groups. Wilder et al. (43) published a separate study using the same group of subjects and supplementation and training protocol, and also reported no significant group or interaction effects for anaerobic muscular endurance (repeated parallel back squat exercise).

Lower doses of Cr supplemented over shorter periods of time have also been shown to be ineffective for increasing anaerobic exercise performance. For example, Hoffman et al. (12) reported that a single Cr dose (Vitalstate US, Inc.; Boynton Beach, FL) of 6 g·d−1 for 6 days had no effect versus PL on BW, peak power, mean power, or total work derived from three 15-second Wingate anaerobic power tests in 40 physically active college-age men. However, the change in the rate of fatigue for the Cr group (n = 20) was significantly (p < 0.05) lower compared to the PL group (n = 20). Although the authors (12) did not directly measure muscle TCr concentrations, they suggested that Cr supplementation may positively affect changes in the rate of fatigue development before it results in beneficial effects on strength and power.

In contrast to the findings of the studies described above, others (6,21,28,31,36) have reported increases in performance following both long-term and short-term supplementation protocols using what might be considered more moderate doses of Cr (8 to 10 g·d−1). For example, Burke et al. (6) reported an ergogenic effect following Cr supplementation for 21 days on force, power, and total work in 41 male college athletes. In their study (6), subjects randomly received either ∼ 7.7 g·d−1 Cr (n = 20) or a PL (n = 21) while participating in a resistance training program (11 sessions) that was designed to increase shoulder strength and musculature (bench press, military press, triceps exercises). Prior to and following supplementation, each subject performed maximal concentric bench press movements until exhaustion on an isokinetic dynamometer. Although both groups showed improvement, the increases in peak force, peak power output, total work, and time to fatigue were all significantly (p < 0.05) greater in the Cr group compared with PL. The authors (6) suggested that the differences in performance were possibly due to a greater increase in BW and, thus, FFW (assessed via skinfolds) in the Cr group (BW Δ = 2.2 kg; p < 0.05) following supplementation versus PL (BW Δ = 0.5 kg; p > 0.05).

Pearson et al. (28) showed that 5 g·d−1 Cr supplementation resulted in significant increases in strength (bench press and squat), power (power clean), and BW compared with PL in 16 NCAA Division I football players during a 10-week resistance training program. In a related study, Tarnopolsky et al. (36) also reported that ingestion of 10 g·d−1 of Cr + 75 g·d−1 of glucose during an 8-week resistance training program using untrained men resulted in similar increases in strength compared to protein + carbohydrate, however, supplementation with Cr led to greater increases in BW.

Magnaris and Maughan (21) examined the effect of short-term Cr supplementation on isometric exercise performance, and reported that 10 g·d−1 (2 × 5 g·d−1) for 5 days resulted in increases in BW (1.7-1.8 kg) and significantly improved the isometric endurance capacity and maximal voluntary isometric force of the leg extensors versus PL in 10 healthy men. Although the findings of Magnaris and Maughan (21) are not in direct agreement with those of Hoffman et al. (12), there are some similarities between the 2 studies, since isometric endurance capacity reflects the rate of fatigue development, and Hoffman et al. (12) also reported a significant effect of Cr on the fatigue index during repeated Wingate tests.

In agreement with Magnaris and Maughan (21), Rossouw et al. (31) also reported that 9 g·d−1 of Cr for 5 or 6 days resulted in significant increases in dead lift volume and maximal intermittent isokinetic exercise performance in experienced power lifters. However, there were no meaningful changes in BW (0.25 kg, p > 0.05) or body composition as measured by skinfolds.

In addition to the differences in the length (6 days to 10 weeks) and amount of Cr supplementation (5-10 g·d−1) reported in the studies above, discrepancies in the findings may also be related to a number of other methodological factors, including the Cr delivery system used (i.e., chewables versus powders versus tablets), the subject characteristics (trained versus untrained), and the types of anaerobic indices used as dependent variables. In the current study, both the CPS and PL groups displayed a wide range of variability in AWC from BL to 30 days (−17.2% to 40.5% and −16.8% to 30.0%, respectively), which likely explains, in part, the finding of no significant effects. Although a familiarization trial was performed, it would appear that some of the subjects experienced a learning effect, since a few individuals in the PL group demonstrated considerable increases in AWC. In addition, the fact that subjects in both groups experienced decrements in performance also suggests that motivation during Critical Power testing may have been a factor, even though they were verbally encouraged throughout the test to provide a maximal effort.

Another major limitation of many of the studies described above (6,12,21,28,31,42), including the current study, is a lack of muscle biopsy data to indicate which subjects were responders (34), and to what degree these different supplementation strategies increased muscle PCr and TCr concentrations. Interestingly, van Loon et al. (38) reported that a maintenance dose of 2 g·d−1 for 37 days actually resulted in a significant decrease in muscle TCr and PCr stores compared with values measured following 5 days of Cr loading (20 g·d−1). However, the increase in free Cr concentration as a result of loading remained elevated with the maintenance dose. In a related study by Preen et al. (30) that showed somewhat contrasting results to those of van Loon et al. (38), the authors (30) compared 2 g·d−1 and 5 g·d−1 maintenance doses for 6 weeks on muscle TCr stores following Cr loading and reported no significant differences between the 2 protocols. However, because the 2 g·d−1 dose resulted in greater urinary excretion of Cr, Preen et al. (30) suggested that larger maintenance doses may be more advantageous for maintaining muscle TCr stores following loading. Preen et al. (30) did not compare the different dosing strategies on any performance-related variables; however, in the study by van Loon et al. (38), 20 young male subjects completed repeated supramaximal sprints on a cycle ergometer following the loading and maintenance phases, and when comparing the mean change scores for peak power and average power, the only significant differences between the PL and Cr groups occurred on day 6 after the loading phase, with the Cr group showing a greater change compared to baseline values. Francaux and Poortmans (10) also reported that a maintenance dose of 3 g·d−1 for 58 days following a 5-day loading phase (21 g·d−1) had no effect on muscle strength compared to PL in 25 young, healthy subjects. Therefore, while a 2-3 g·d−1 maintenance dose may be effective for maintaining increases in free Cr following loading, it may not be effective for maintaining improvements in anaerobic performance.

The efficacy of a single serving of low-dose Cr administration for enhancing anaerobic exercise performance remains unclear; however, considering the results of the current study, and those of several similar studies (8,9,33), it would appear that supplementation involving a loading dose of Cr for at least 2-3 days is superior to a single dose of 5 g·d−1 for 30 days for increasing AWC. In addition, the current findings, as well as the results of several other studies that used low to moderate doses of Cr supplementation (2 to 10 g·d−1) without a loading phase (6,12,21,28,31,36,37,42), indicate that the Cr dosage for supplementation protocols lasting 1-4 weeks, and possibly up to 10 weeks, range between 8 and 10 g·d−1 to enhance anaerobic performance and FFW, and that 5 g·d−1 be used as a minimum dose for supplementation protocols lasting ≥ 10 weeks. Given the results of van Loon et al. (38) who found that 2 g·d−1 of Cr during a 6-week maintenance phase actually decreased muscle TCr and PCr concentrations, and considering that normal daily losses of Cr are ∼2-3 g·d−1 (3,23), it may seem reasonable to recommend that maintenance doses following loading also be no less than 5 g·d−1. Future studies are warranted which directly measure muscle TCr and PCr stores following Cr dosing strategies designed to more slowly load the muscles and determine their effectiveness on various measures of anaerobic performance.

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Practical Applications

Several studies have shown that Cr and CPS loading (i.e., 4 × 5 g·d−1 × 5-7 d) significantly increase high intensity exercise performance, including AWC (8,9,33). However, the results of the current study, as well as those of Hoffman et al. (12), indicate that a single serving of ≤6 g·d−1 Cr supplementation for ≤4 weeks may not be as effective as other dosing strategies for increasing muscle TCr and PCr concentrations and enhancing high intensity anaerobic performance. Because several studies have shown that 2-3 days of loading (20-25 g·d−1) is sufficient to increase PCr stores (14,39) and/or increase anaerobic performance (9,29,44), it is recommended that Cr supplementation protocols include a loading dose for at least 2 days before beginning a maintenance dose for optimal results. If a loading dose is not well tolerated, as is the case with some athletes and is not feasible, it is recommended that 8 to 10 g·d−1 be ingested for supplementation protocols lasting up to 10 weeks, whereas doses as low as 5 g·d−1 appear to be effective if supplementation will occur long-term (≥10 weeks). Based upon the findings of van Loon (38) and Francaux and Poortmans (11), it would also appear that maintenance doses following loading be no less than 5 g·d−1 to maximize results.

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Acknowledgments

This study was supported by a grant from NUMICO Research, Wageningen, The Netherlands.

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Keywords:

critical power test; ergogenic aids; dietary supplement

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