Creatine supplementation significantly improves both upper and lower body strength (WMD = 4.43 kg and 11.35 kg, respectively). The meta-analysis utilizes WMD, a methodological strength. Key limitations include potential publication bias (evidenced by funnel plot asymmetry) and study heterogeneity. The inclusion of forest plots and the exploration of sex differences enhance the analysis.
The meta-analysis demonstrates a statistically significant positive effect of creatine supplementation on both upper and lower body strength, with a weighted mean difference (WMD) of 4.43 kg for upper body and 11.35 kg for lower body. The use of WMD is a methodological strength, allowing for direct interpretation of the effect size in kg. However, limitations such as potential publication bias (indicated by the funnel plot asymmetry) and the heterogeneity of included studies warrant cautious interpretation. The exploration of sex differences and the inclusion of forest plots enhance the analysis, contributing valuable insights into the effects of creatine supplementation.
The abstract clearly states the main objective of the systematic review and meta-analysis, which is to investigate the effects of creatine supplementation and resistance training on muscle strength gains in adults under 50 years of age, considering the influence of variables such as age, training duration, and sex.
The abstract effectively summarizes the methodology employed in the review, including the databases searched, the search end date, and the number of studies included, specifying the number of male and female participants.
This is a high-impact suggestion that would enhance the clarity and informativeness of the abstract. The abstract should explicitly state the specific types of creatine used in the included studies, as this information is crucial for interpreting the results and for the reproducibility of the study. Different forms of creatine may have varying effects on muscle strength, and specifying the type used allows for a more accurate assessment of the intervention's efficacy. This would also aid future research in selecting the appropriate creatine form for their studies. Clearly stating the creatine form used in the abstract improves the transparency and scientific rigor of the review.
Implementation: Add a sentence to the Methods section of the abstract specifying the type of creatine used in the included studies. For example, "All included studies used creatine monohydrate supplementation." If different forms of creatine were used, specify the different forms and the number of studies using each form.
The introduction effectively establishes the context of creatine supplementation as a widely used ergogenic aid, particularly in strength-based sports and activities.
This is a high-impact suggestion as it would enhance the introduction by providing a more focused and specific rationale for the study. While the introduction mentions the limitations of previous meta-analyses, it doesn't explicitly state the gap in knowledge that this study aims to fill. Clearly defining this gap would strengthen the rationale and highlight the study's unique contribution. This would also improve the reader's understanding of the study's purpose and its importance within the existing literature. Adding a clear statement about the knowledge gap would significantly improve the introduction by providing a more compelling justification for the study.
Implementation: Add a sentence or two after the discussion of previous meta-analyses, clearly stating the specific gap in knowledge this study addresses. For example, "However, there is a lack of research specifically investigating the effects of creatine supplementation on strength gains in adults under 50 years of age, considering the influence of sex and training variables. This study aims to address this gap by..."
This is a medium-impact suggestion that would improve the clarity and organization of the introduction. While the introduction mentions the general benefits of creatine, it would be beneficial to provide a more concise and structured overview of the hypothesized mechanisms by which creatine improves muscle strength. This would help readers understand the physiological basis of the study and connect it to the subsequent sections. Providing a structured overview of the hypothesized mechanisms would enhance the introduction by offering a clear roadmap for the reader and setting the stage for the subsequent sections on methods and results. This would improve the overall flow and coherence of the paper.
Implementation: Add a paragraph after the general introduction of creatine, outlining the hypothesized mechanisms by which creatine improves muscle strength. Use bullet points or numbered lists to clearly present each mechanism. For example, "Creatine is hypothesized to improve muscle strength through several mechanisms: 1) Increased ATP resynthesis, 2) Enhanced glycogen storage, 3) Reduced muscle damage."
The search strategy is comprehensive, using multiple databases (MEDLINE, Scopus, Embase, and SPORTDiscus) and a combination of MeSH terms and free text words. This approach maximizes the likelihood of capturing all relevant studies.
The authors clearly define the eligibility criteria using the PICOS framework, specifying the population, intervention, comparison, outcome, and study design. This provides transparency and allows for easy assessment of the included studies' relevance.
This is a high-impact suggestion that would enhance the reproducibility and transparency of the study. The Methods section should provide the full search strategies used for each database, including specific keywords and search filters. This information is crucial for allowing other researchers to replicate the search and evaluate its comprehensiveness. Providing the full search strategy strengthens the paper by ensuring that the search process is transparent and auditable. This would also facilitate future updates of the review and allow for comparisons with other systematic reviews on the same topic. Ultimately, including the full search strategies would significantly improve the study's scientific rigor and reproducibility.
Implementation: Add a supplementary file or an appendix to the paper containing the full search strategies used for each database (MEDLINE, Scopus, Embase, and SPORTDiscus). Include the specific keywords, MeSH terms, Boolean operators, and any filters applied. Provide the date the searches were conducted.
This is a medium-impact suggestion that would improve the clarity and rigor of the study. The Methods section should specify the process used for assessing the risk of bias in the included studies. This is important for understanding the potential limitations of the evidence and for interpreting the results of the meta-analysis. Specifying the risk of bias assessment tool and process strengthens the paper by providing transparency and allowing readers to assess the overall quality of the included studies. This would also help to contextualize the findings and inform future research. Ultimately, including a risk of bias assessment would improve the study's methodological rigor and the reliability of its conclusions.
Implementation: Specify the tool used for assessing the risk of bias (e.g., Cochrane Risk of Bias tool, PEDro scale). Describe the process used for applying the tool, including who performed the assessment and how discrepancies were resolved. Present the results of the risk of bias assessment in a table or figure, summarizing the risk of bias for each included study.
Table 1. PICOS criteria for the inclusion of RCTs in which the supplementation of creatine was combined with a well-structured resistance training program and pre-post-training strength gain was compared with placebo supplementation with resistance training.
The results section systematically presents the findings of the meta-analysis, starting with the study selection process and progressing through the main outcomes and subgroup analyses. This structured approach facilitates reader comprehension and ensures all key findings are clearly presented.
The authors provide clear and concise descriptions of the included studies' characteristics, including participant demographics, creatine protocols, and training protocols. This detailed information allows readers to understand the context of the meta-analysis and assess the generalizability of the findings.
This is a high-impact suggestion that would enhance the interpretation and clinical relevance of the findings. The Results section should include a discussion of the magnitude of the observed effects, such as by interpreting the WMD values in the context of minimal clinically important differences (MCID). This would help readers understand the practical significance of the findings and whether the observed strength gains are meaningful in real-world scenarios. Providing this context would strengthen the paper by bridging the gap between statistical significance and clinical relevance, making the results more impactful for practitioners and researchers. Ultimately, discussing the magnitude of effects in relation to MCID would significantly improve the clinical applicability and translational value of the findings.
Implementation: Interpret the WMD values for upper and lower body strength in the context of established MCIDs for these outcomes. If no established MCID exists, discuss the magnitude of the effects in relation to other relevant benchmarks or clinical guidelines. For example, "The observed WMD of 4.43 kg for upper body strength exceeds the MCID of 2 kg reported by [reference], suggesting a clinically meaningful improvement."
This is a medium-impact suggestion that would improve the clarity and visual appeal of the results. The figures presenting the forest plots (Figures 2 and 4) could be enhanced by including additional information, such as the study weights and I-squared values directly on the figures. This would make the figures more self-explanatory and easier to interpret without needing to refer back to the text. Adding this information directly to the figures would strengthen the paper by improving the visual presentation of the data and facilitating a quicker understanding of the meta-analysis results. This would also enhance the figures' suitability for presentations and other dissemination formats. Ultimately, enhancing the forest plots with study weights and I-squared values would improve the clarity and accessibility of the key findings.
Implementation: Add the study weights (represented by the size of the squares in the forest plot) and the I-squared value for heterogeneity directly onto Figures 2 and 4. Ensure the figure legends clearly explain these additions.
Table 2. Evaluation of the methodological quality of eligible studies (n = 23) utilizing the Physiotherapy Evidence Database (PEDro) scale.
Table 3. Information on the studies that were included in the systematic review (n = 23).
Figure 2. Effect of creatine supplementation and resistance training compared with a placebo and resistance training on upper-body strength. The red circle represents the pooled weighted mean difference following a random effect meta-analysis, expressed in kg.
Figure 3. Subgroup analyses for creatine supplementation combined with resistance training on upper-body muscle strength compared with placebo supplementation combined with resistance training. MD, mean difference (kg); P1, p-value for the within-subgroup comparison (i.e., pre-post-intervention changes within each subgroup); P2, p-value for the between-subgroup comparison (i.e., comparison of the pre-post-intervention changes between subgroups); NA, Not Available.
Figure 4. Effect of creatine supplementation and resistance training compared with a placebo and resistance training on lower-body muscle strength. The red circle represents the pooled weighted mean difference following a random effect meta-analysis, expressed in kg.
Figure 5. Subgroup analyses for creatine supplementation and resistance training compared with a placebo and resistance training on lower-body strength. MD, mean difference(kg); P1, p-value for the within-subgroup comparison (i.e., pre-post-intervention changes within each subgroup); P2, p-value for the between-subgroup comparison (i.e., comparison of the pre-post intervention changes between subgroups); NA, Not Available.
Figure 6. Observed and imputed funnel plot for upper-body muscle strength. The funnel plot displays the distribution of studies included in this meta-analysis, with white circles representing the original observed studies and black circles indicating the imputed studies added to account for potential publication bias using the trim and fill method. At the bottom of the funnel plot, the white and black diamonds represent the combined effect sizes, with the white diamond indicating the overall effect from the observed studies, and the black diamond showing the adjusted effect after imputation.
Figure 7. Observed and imputed funnel plot for lower-body muscle strength. The funnel plot displays the distribution of studies included in this meta-analysis, with white circles representing the original observed studies. At the bottom of the funnel plot, the white and black diamonds represent the combined effect sizes, with the white diamond indicating the overall effect from the observed studies and the black diamond showing the adjusted effect after imputation.
The discussion effectively summarizes the main findings of the meta-analysis, highlighting the significant improvement in upper and lower body strength with creatine supplementation combined with resistance training in adults under 50.
The discussion provides context for the findings by referencing previous meta-analyses and discussing the potential mechanisms underlying the observed effects of creatine supplementation on muscle strength.
This is a high-impact suggestion as it strengthens the discussion by providing a more nuanced interpretation of the findings. The discussion should elaborate on the clinical significance of the observed strength gains. While the meta-analysis reports the WMD in kg, it lacks a discussion of whether these gains are practically meaningful for athletes and individuals engaged in resistance training. Adding a discussion of the minimal clinically important difference (MCID) or other relevant benchmarks would provide valuable context and enhance the practical implications of the findings. This would also strengthen the paper's contribution to the field by providing a more comprehensive understanding of the effects of creatine supplementation.
Implementation: Include a discussion of the MCID for strength gains in the context of resistance training. If an established MCID is available, compare the observed WMD values to the MCID. If not, discuss the magnitude of the effects in relation to other relevant benchmarks or practical guidelines. For example, "The observed WMD of 11.35 kg for lower-body strength represents a substantial increase, exceeding the MCID of X kg reported by [reference], suggesting a clinically meaningful improvement."
This is a medium-impact suggestion that would improve the discussion's depth and connect it more strongly to the results. The discussion mentions the subgroup analysis on sex differences but could be strengthened by exploring the potential reasons for the observed differences in more detail. Elaborating on the potential physiological and hormonal factors contributing to the blunted response in females would provide a more comprehensive understanding of the findings. This would also enhance the discussion's scientific rigor and contribute to a more nuanced interpretation of the results.
Implementation: Expand the discussion on sex differences by elaborating on the potential physiological and hormonal factors that may contribute to the blunted response to creatine supplementation in females. Discuss factors such as higher pre-supplementation intramuscular creatine levels, differences in amino acid catabolism, and the influence of menstrual cycle fluctuations and estrogen levels. For example, "The blunted response in females may be related to higher baseline intramuscular creatine levels, as reported by [reference], which could limit the potential for further increases with supplementation."
The conclusions section concisely summarizes the main findings of the meta-analysis, clearly stating the significant improvement in upper and lower body strength with creatine supplementation combined with resistance training.
The conclusion effectively synthesizes the results by quantifying the strength improvements observed with creatine supplementation, providing specific weighted mean differences (WMD) in kg for both upper and lower body strength.
This is a high-impact suggestion that would enhance the conclusions by acknowledging the limitations of the study. While the discussion section mentions limitations, briefly reiterating key limitations in the conclusion reinforces their importance and promotes cautious interpretation of the findings. This strengthens the paper's scientific rigor and transparency.
Implementation: Add a sentence briefly acknowledging key limitations, such as the variability in creatine protocols and the limited female representation. For example, "These findings should be interpreted considering the variability in creatine protocols and the limited female representation in the included studies."
This is a medium-impact suggestion that would enhance the conclusion by providing more specific recommendations for future research. While the conclusion mentions the need for further research, it could be strengthened by outlining specific research questions or areas of investigation. This would provide a more actionable roadmap for future studies and contribute to the advancement of the field.
Implementation: Expand the sentence on future research to include specific recommendations. For example, "Future research should prioritize investigating the optimal combination of creatine dosage and resistance training protocols for maximizing strength gains in both males and females, as well as exploring the potential benefits of creatine supplementation in various athletic populations."