Does oral creatine supplementation improve strength? A meta-analysis

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Original Research

Does oral creatine supplementation improve strength? A meta-analysis

J Fam Pract. 2002 November;51(11):945-952

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References

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Data abstraction and statistical analysis

Two independent reviewers abstracted data, and a third reviewer resolved differences. For studies investigating multiple sprints, data from the first sprint only were included in statistical analysis because the first sprint is when peak power achievement is expected. A weighted mean difference (WMD) between creatine and placebo groups was calculated for each outcome using Review Manager 4.1 software (developed by The Cochrane Collaboration). A fixed effects model was used unless statistical heterogeneity was significant (P < .05), in which case a random effects model was used. Subanalyses were planned on several factors that were anticipated to be sources for variation, including (1) dose and duration of creatine administration, (2) concomitant resistance training, (3) different baseline level of physical training, (4) age, and (5) sex.

Results

Description of studies

After reviewing titles and available abstracts of more than 500 articles, we retrieved 66 potentially relevant studies, 16 of which met inclusion criteria for the analysis.^17,20-34 Characteristics of these studies are summarized in the Table. Included studies represented 20 discrete samples and 414 subjects. Two studies^20,21 evaluated creatine supplementation in men older than 60 years, whereas all the others studied younger subjects (range, 18–36 years). Only 1 study included women.¹⁷ Creatine dosages were similar across included studies (typically 20 g/d for the first 4–7 days of supplementation and 5 g/d thereafter). Studies that evaluated maximal weight lifting performance were more likely to include adjuvant resistance training programs in their protocols than those that evaluated cycle ergometry sprint or isokinetic dynamometer performance. None included cycle ergometry training.

TABLE

Characteristics of included studies

Reference	No. subjects (sex)	Dose per day and duration	Training level	Weight training during study?	Outcome measurement	Quality score (out of 10)	Comparability of creatine & placebo groups at baseline*
Barnett 1996	17 (M)	280 mg/kg ×4 d	Active	No	CP	2.5	+
Cooke 1995	12 (M)	20 g ×5 d	Untrained	No	CP	2.5	+
Cooke 1997^†	80 (M)	20 g ×5 d	Trained or active	No	CP	2	+++
Dawson 1995^‡	18 (M), 22(M)	20 g ×5 d	Active	No	CP	3	+++
Jones 1999	16 (M)	20 g ×5 d then 5 g ×10 wk	Trained	Yes	CM	3	+++
Stone 1999	20 (M)	0.22 g/kg ×35 d	Trained	Yes	CM, BP, S	4.5	+++
Kelly 1998	18 (M)	20 g ×5 d then 5 g ×26 d	Trained	Yes	3BP	2	–
Noonan 1998	39 (M)	20 g ×5 d then 300 mg/kg ×8 wk	Trained	Yes	BP	5.5	+++
Peeters 1999	35 (M)	20 g ×3 d then 10 g ×6 wk	Trained	Yes	BP	3	+++
Vandenberghe 1997	19 (F)	20 g ×4 d then 5 g ×10 wk	Untrained	Yes	BP, S	5	+++
Pearson 1999	16 (M)	5 g ×10 wk	Trained	Yes	BP, S, PT	3	+++
Volek 1999	19 (M)	25 g ×7 d then 5 g ×12 wk	Trained	Yes	BP, S	4.5	+++
Gilliam 2000	23 (M)	20 g ×5 d	Active but untrained	No	PT	2.5	+
Rawson 1999^§	20 (M)	20 g ×10 d then 4 g ×20 d	Untrained	No	AF, PT	4.5	+++
Rawson 2000^§	17 (M)	20 g ×5 d	Untrained	No	AF	3.5	+++
Becque 2000	23 (M)	20 g ×5 d then 2 g ×6 wk	Trained	Yes	AF	5	+
*Comparability between groups was assessed for age, anthropomorphic measurements, and strength outcomes. +++ = similar for all 3 characteristics; + = similar for strength outcome measurements; – = not comparable at baseline for strength outcome.
^†Four protocols with 20 subjects each evaluating the same strength outcome measurement reported in Cooke 1997.
^‡Two separate experiments reported in Dawson 1995.
^§Included subjects > 60 years old; in all others subjects were < 36 years old.
AF, 1 repetition maximum arm flexor strength; BP, 1 repetition maximum bench press strength; 3BP, 3 repetition maximum bench press strength; CM, cycle ergometer mean peak power; CP, cycle ergometer peak power; PT, isokinetic leg flexion/extension peak torque; S, 1 repetition maximum squat strength.

Methodological quality of included studies

The methodological quality of studies was generally low (Table). The mean quality score was 3.5 ± 1.2 (mean ± SD) out of a possible 10 (range, 2–5.5). None of the studies identified the method of randomization used or specifically reported an intention-to-treat analysis. None specifically reported masking of outcome assessment. In general, these significant flaws in study design would tend to result in overestimation of the benefit of creatine supplementation.

Absolute strength

When 1- to 3-repetition maximum bench press strength measurements were statistically combined (they were homogeneous), the creatine supplementation group showed an absolute strength increase of 6.85 kg (95% confidence interval [CI], 5.24–8.47; n = 143) lifted per repetition greater than that seen with placebo alone (Figure 1). There was no additional advantage in strength performance after 9 to 12 weeks of supplementation (WMD = 6.6 kg; 95% CI, 3.5–9.5) compared with 4 to 8 weeks of supplementation (WMD = 6.6 kg; 95% CI, 4.8–8.4). Subanalysis for an interaction with resistance training, previous training level, age, or sex was not possible because all studies measuring bench press strength except one¹⁷ investigated creatine supple mentation in previously trained young men who continued resistance training during supplementation. The 1 study in previously sedentary young women¹⁷ did find a trend toward increased bench press strength, although independently this change was not statistically significant.