The intensity paradox: A systematic review and meta-analysis of its impact on the cardiorespiratory fitness of older adults

Table of Contents

Overall Summary

Study Background and Main Findings

This systematic review and meta-analysis investigated the impact of moderate- versus high-intensity aerobic exercise on cardiorespiratory fitness (CRF) in older adults, with a specific focus on accounting for total exercise volume. The meta-regression analysis showed a moderate, but not statistically significant, relationship between exercise intensity and improvements in VO2peak after accounting for the completed exercise volume (β = 0.31, 95% CI = [-0.04; 0.67], z = 1.74). Direct comparison between moderate- and high-intensity groups revealed a small, non-significant effect favoring high-intensity exercise (Hedges' g = 0.20, 95% CI = [-0.02; 0.41]). Overall, aerobic exercise demonstrated a moderate-to-large positive effect on VO2peak (Hedges' g = 0.75, 95% CI = [0.58; 0.93]), with both moderate-intensity (Hedges' g = 0.60, 95% CI = [0.28; 0.92]) and high-intensity (Hedges' g = 0.82, 95% CI = [0.61; 1.02]) groups showing significant improvements.

Research Impact and Future Directions

The study provides valuable insights into the relationship between aerobic exercise intensity and CRF improvements in older adults, particularly by accounting for exercise volume. While the results suggest that both moderate- and high-intensity exercise can improve CRF, the study does not find strong evidence to support the superiority of one over the other when volume is considered. This challenges the common belief that high-intensity exercise is inherently more effective and highlights the importance of total exercise volume.

The practical utility of these findings lies in their potential to inform more flexible and individualized exercise prescriptions for older adults. The study suggests that a wider range of exercise intensities may be effective, allowing for greater personalization based on individual preferences and abilities. This could lead to improved exercise adherence and, consequently, better health outcomes. The findings also place the study within the context of existing research by aligning with some previous findings while also highlighting discrepancies, potentially due to differences in methodology and the inclusion of exercise volume as a key variable.

For practitioners, the study emphasizes the importance of considering individual preferences and abilities when designing exercise programs for older adults. While high-intensity exercise may offer some benefits, it is not the only effective approach. Moderate-intensity exercise, which may be more accessible and appealing to some individuals, can also lead to significant improvements in CRF. However, it is crucial to acknowledge that individual responses to exercise can vary considerably, and a personalized approach is likely to be most effective. The study also highlights the potential benefits of shorter exercise interventions, which could be particularly relevant for older adults who may have difficulty adhering to longer programs.

Critical unanswered questions include the precise mechanisms underlying the observed effects of different exercise intensities and the optimal exercise volume for maximizing CRF improvements in older adults. Additionally, while the study accounted for exercise volume, the specific way in which it was calculated and standardized could influence the results. Methodological limitations, such as moderate heterogeneity among the included studies and the relatively small number of studies in some analyses, suggest that the findings should be interpreted with some caution. These limitations do not fundamentally undermine the study's conclusions, but they highlight the need for further research to confirm and refine these findings.

Critical Analysis and Recommendations

Comprehensive Literature Search (written-content)
The abstract clearly outlines a systematic approach to searching multiple relevant databases, ensuring a thorough review of the existing literature. This increases the likelihood of capturing all relevant studies and enhances the robustness of the findings.
Section: Abstract
Clarify Exercise Volume Adjustment (written-content)
The abstract does not specify how exercise volume was accounted for or standardized across studies. Providing this detail would enhance the study's methodological rigor and transparency, allowing readers to better understand how this crucial variable was handled.
Section: Abstract
Well-Defined Research Gap (written-content)
The introduction identifies a clear research gap by pointing out the lack of studies investigating exercise intensity's impact on CRF in older adults while accounting for exercise volume. This highlights the study's novelty and its contribution to addressing an important unanswered question in the field.
Section: INTRODUCTION
Elaborate on Exercise Volume Calculation (written-content)
The methods section lacks a detailed explanation of how exercise volume was calculated and standardized across different studies. Providing a more thorough description of this critical variable is essential for ensuring reproducibility and allowing readers to fully understand the nuances of the study's methodology.
Section: MATERIALS AND METHODS
Comprehensive Search Strategy (written-content)
The study employs a thorough and systematic search strategy adhering to the PRISMA guidelines. This ensures a comprehensive review of the relevant literature, increasing confidence in the completeness of the included studies.
Section: MATERIALS AND METHODS
Visual Clarity of Flowchart (graphical-figure)
Figure 1, the PRISMA flowchart, is visually clear, well-organized, and presents the study selection process transparently. This allows readers to easily understand the flow of studies through the review and assess the rigor of the selection process.
Section: MATERIALS AND METHODS
Clear Presentation of Meta-Regression Analysis (written-content)
The results section clearly presents the meta-regression analysis, including effect size, confidence interval, and z-value. This allows for a proper understanding of the relationship between exercise intensity and VO2peak improvements, even though the relationship was not statistically significant.
Section: RESULTS
Comprehensive Synthesis of Evidence (written-content)
The discussion effectively synthesizes the study's findings, providing a comprehensive overview of the relationship between exercise intensity, volume, and CRF improvements in older adults. This allows readers to grasp the main takeaways and their implications.
Section: DISCUSSION
Expand on Practical Implications for Exercise Prescription (written-content)
The conclusion does not fully elaborate on the practical implications of the findings for exercise prescription in older adults. Providing more specific guidance on how these findings can be translated into recommendations would increase the paper's impact on clinical practice and public health guidelines.
Section: CONCLUSION

Section Analysis

Abstract

Key Aspects

Strengths

Suggestions for Improvement

INTRODUCTION

Key Aspects

Strengths

Suggestions for Improvement

MATERIALS AND METHODS

Key Aspects

Strengths

Suggestions for Improvement

Non-Text Elements

Figure 1 Flowchart of the systematic review and meta-analysis according to the...
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Figure 1 Flowchart of the systematic review and meta-analysis according to the PRISMA guidelines. Updated search: 09.05.2023.

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Figure 1 Flowchart of the systematic review and meta-analysis according to the PRISMA guidelines. Updated search: 09.05.2023.
First Reference in Text
searched simultaneously (Figure 1).
Description
  • Overview: This element is a flowchart, which is a diagram that visually represents a process or workflow. In this case, it illustrates the steps taken in a systematic review and meta-analysis. A systematic review is a method of identifying, evaluating, and synthesizing all available research evidence relevant to a particular research question. A meta-analysis is a statistical technique used to combine the results of multiple studies to arrive at a single, overall estimate of effect. This flowchart is structured according to the PRISMA guidelines, which stands for Preferred Reporting Items for Systematic Reviews and Meta-Analyses. PRISMA is a widely accepted standard that provides a checklist of items to include when reporting systematic reviews and meta-analyses, aiming to improve transparency and completeness.
  • Identification Phase: The first stage depicted is 'Identification'. This involves finding all potentially relevant studies. The flowchart shows two main sources: databases and registers, and 'other methods'. The database search includes CENTRAL (a database of clinical trials), EMBASE (a biomedical and pharmacological database), and MEDLINE (a database of life sciences and biomedical information). Each database search yielded a specific number of records, which are documents or entries within the database. 'Other methods' include looking through citations and contacting authors for additional information. This phase resulted in 9673 total records.
  • Screening Phase: Next is the 'Screening' phase. Here, the researchers removed duplicate records, which are identical entries that appear multiple times, using tools like Ovid, EndNote, and Rayyan. This is a common step in systematic reviews to ensure that the same study isn't counted multiple times. After removing duplicates, 5188 records remained. These records were then screened, likely by reading titles and abstracts, to exclude those that clearly didn't meet the study's criteria. This resulted in 337 reports being sought for retrieval, meaning the full text of these articles was obtained.
  • Eligibility and Inclusion Phase: The 'Eligibility' phase involves a detailed assessment of the 337 full-text articles to determine if they meet the specific criteria for inclusion in the review. The flowchart lists reasons for exclusion, such as 'Data from other study', 'Population', 'CRF test', etc. This means that articles were excluded if they used data already included in another study, didn't focus on the right population, didn't use the correct type of cardiorespiratory fitness (CRF) test, and so on. After this rigorous assessment, 23 studies were included in the review.
  • Meta-Analysis Inclusion: Finally, the flowchart indicates which studies were included in the meta-analysis. A meta-analysis, as mentioned earlier, is a statistical synthesis of results. The flowchart shows that 15 studies were included in one part of the meta-analysis (Figure 2) and 7 in another (Figure 3).
Scientific Validity
  • Comprehensive Search Strategy: The search strategy is comprehensive, utilizing multiple databases (CENTRAL, EMBASE, MEDLINE) and supplementary methods like citation searching and author correspondence. This multi-faceted approach enhances the likelihood of capturing all relevant studies, a critical aspect of robust systematic reviews.
  • PRISMA Guidelines Adherence: The flowchart explicitly states adherence to PRISMA guidelines, which is the gold standard for reporting systematic reviews and meta-analyses. This adherence suggests a commitment to transparency and methodological rigor.
  • Duplicate Removal: The process for removing duplicate records is clearly outlined and utilizes appropriate tools (Ovid, EndNote, Rayyan). This is crucial for preventing overestimation of effects due to the same study being counted multiple times.
  • Detailed Exclusion Criteria: The flowchart provides specific reasons for excluding reports during the eligibility assessment. This level of detail allows for scrutiny of the selection process and ensures that the inclusion criteria were applied consistently and appropriately.
  • Clear Inclusion Numbers: The number of studies included in the review (23) and in each part of the meta-analysis (15 and 7) is clearly stated. This transparency allows readers to understand the scope of the analysis and the amount of data contributing to the findings.
Communication
  • Visual Clarity: The flowchart is visually clear and well-organized, using standard flowchart symbols and a logical left-to-right, top-to-bottom flow. The use of different colors for each stage (identification, screening, inclusion) further enhances readability.
  • Concise Labeling: The labels within each box are concise and informative, providing sufficient detail without being overly verbose. The use of abbreviations (e.g., 'CRF test', 'N/A') is appropriate and likely understood by the target audience.
  • Numerical Transparency: The flowchart clearly presents the number of records/reports at each stage of the process, allowing readers to easily track the flow of studies through the review. This numerical transparency is essential for understanding the scope and limitations of the review.
  • Specific Exclusion Reasons: The inclusion of specific reasons for excluding reports enhances the transparency of the selection process. This allows readers to understand the criteria used to determine study eligibility.
  • Cross-referencing: The flowchart effectively cross-references other figures in the paper (Figure 2 and Figure 3), indicating where the results of the meta-analysis are presented. This helps readers connect the different parts of the study.
TABLE 1 Overview of the study characteristics in the systematic review.
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TABLE 1 Overview of the study characteristics in the systematic review.
First Reference in Text
The complete search string can be found in Table S1 in Data S1.
Description
  • Purpose: This element is a table, labeled Table 1, that summarizes the key characteristics of the studies included in the systematic review. A systematic review, as mentioned before, is a comprehensive assessment of existing research on a specific topic. This table provides a snapshot of the studies that were deemed relevant and included in this particular review.
  • Table Structure: The table is organized into columns and rows. Each row represents a different study, and each column represents a specific characteristic of those studies. This structure allows for a systematic comparison of the studies based on these characteristics.
  • Column Headings: The columns are labeled with headings that describe the type of information presented in that column. These headings include 'Study' (which likely refers to the authors and year of publication), 'Country', 'Sample size incl. in analysis (n)' (which indicates the number of participants in each study), 'Primary outcome' (the main variable being measured), 'Secondary outcome' (other variables measured), 'Age range (years)', and 'Female (%)' (the percentage of female participants in each study).
  • Study Identification: The 'Study' column lists the studies included in the review, using the first author's last name and the year of publication (e.g., 'Andrade et al.40' likely refers to a study by Andrade and colleagues published in the year associated with reference number 40 in the paper's bibliography). This allows readers to easily locate the original studies if they want more detailed information.
  • Geographic and Demographic Information: The table provides information about where each study was conducted ('Country') and the characteristics of the participants, such as their age range and the percentage of females. This helps readers understand the context of the studies and the populations they focused on. For example, we can see that studies were conducted in various countries like Brazil, the USA, Australia, Italy, and Sweden.
  • Outcome Measures: The 'Primary outcome' and 'Secondary outcome' columns indicate what each study was measuring. The primary outcome is often listed as 'VO2peak', which is a measure of cardiorespiratory fitness. It represents the maximum amount of oxygen a person can utilize during intense exercise. Secondary outcomes vary across studies and include things like endurance parameters, cognitive function, physical activity level, and body composition. These outcomes reflect the different aspects of health and fitness that the studies were investigating.
Scientific Validity
  • Relevance to Research Question: The table includes studies that are directly relevant to the research question, as evidenced by the consistent focus on VO2peak as a primary outcome, which aligns with the paper's focus on cardiorespiratory fitness.
  • Sample Size Reporting: The table clearly reports the sample size for each study, which is crucial for assessing the statistical power and generalizability of the findings. The sample sizes vary considerably, which is important to consider when interpreting the results of the meta-analysis.
  • Demographic Data Inclusion: The inclusion of demographic data (age range and sex distribution) allows for an assessment of the diversity and representativeness of the study populations. This is important for understanding the potential limitations and applicability of the findings to different groups.
  • Outcome Measure Consistency: The primary outcome, VO2peak, is consistently reported across studies, which is essential for a meaningful meta-analysis. The inclusion of secondary outcomes provides a broader context for understanding the effects of the interventions.
Communication
  • Clear and Organized Structure: The table is well-organized and easy to read, with clear column headings and a logical arrangement of information. The use of abbreviations is appropriate and consistent with scientific conventions.
  • Concise Presentation: The table presents a large amount of information in a concise and accessible format. This allows readers to quickly grasp the key characteristics of the included studies without being overwhelmed by detail.
  • Effective Use of Abbreviations: The table uses standard abbreviations (e.g., 'incl.' for included, 'n' for sample size, 'VO2peak' for peak oxygen uptake) that are likely to be familiar to the target audience. This helps to keep the table compact and readable.
  • Study Identification Clarity: The 'Study' column clearly identifies each study using the first author's last name and year of publication, facilitating easy cross-referencing with the paper's bibliography.
  • Footnotes for Clarification: The table includes footnotes that provide additional information or clarification where needed. For example, footnote 'a' explains that a particular study was part of a larger study comparing different exercise modalities, and footnote 'b' indicates that a study was included due to author correspondence. These footnotes enhance transparency and provide valuable context.
TABLE 2 Characteristics of the aerobic exercise interventions and methods for...
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TABLE 2 Characteristics of the aerobic exercise interventions and methods for testing cardiorespiratory fitness.

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TABLE 2 Characteristics of the aerobic exercise interventions and methods for testing cardiorespiratory fitness.
First Reference in Text
The reviewers SHF and JF independently extracted in- formation regarding the study population: country, sam- ple size, outcomes, age, and sex (Table 1).
Description
  • Purpose: This table, Table 2, provides detailed information about the specific exercise programs used in each study and how cardiorespiratory fitness was measured. Think of it as providing the 'recipe' for the exercise interventions and the methods used to assess their effectiveness. It builds upon Table 1 by providing a deeper dive into the 'how' of each study, whereas Table 1 focused more on the 'who' and 'where'.
  • Table Structure: Similar to Table 1, this table is organized with rows representing individual studies and columns representing different characteristics of the exercise interventions and testing methods. This allows for a systematic comparison of these aspects across the studies.
  • Column Headings: The columns in this table are more technical and focus on the specifics of the exercise interventions. They include headings like 'Protocol type' (the general type of exercise program), 'Group' (the specific exercise group within a study), 'Freq./wk.' (how many times per week the exercise was performed), 'Intended int. range' (the planned intensity of the exercise), 'Int. cat.' (the intensity category, such as moderate or high), 'Int. monitoring' (how the intensity was tracked), 'Achieved int.' (the actual intensity achieved during the exercise), 'Duration main session (min)' (how long each exercise session lasted), 'Duration (wk)' (the total duration of the intervention in weeks), 'Attendance' (the percentage of sessions attended), 'Weekly min. and MET's' (the total exercise time per week and the metabolic equivalents, a measure of exercise intensity), 'VO2peak test' (the method used to measure peak oxygen uptake), and 'Pre-post VO2peak (mL/kg/min)' (the peak oxygen uptake before and after the intervention).
  • Intervention Details: The table provides a comprehensive overview of the exercise interventions, including the type of exercise (e.g., walking, cycling, dancing), the frequency and duration of sessions, and the intended and achieved exercise intensity. Exercise intensity is often described using terms like percentage of maximum heart rate (HRmax) or heart rate reserve (HRR). HRmax is the highest heart rate a person can achieve during maximal exertion, while HRR is the difference between HRmax and resting heart rate. These measures are used to gauge how hard someone is exercising relative to their maximum capacity. The table also describes how intensity was monitored, such as using heart rate monitors or subjective scales like the rating of perceived exertion (RPE), which is a way for people to rate how hard they feel they are exercising on a numerical scale.
  • Cardiorespiratory Fitness Testing: The table also details how cardiorespiratory fitness was assessed in each study. This usually involved measuring VO2peak, which, as we know from Table 1, is the maximum amount of oxygen a person can use during intense exercise. The 'VO2peak test' column specifies the method used, such as a treadmill test (TM) or a cycle ergometer test (CE). The 'Pre-post VO2peak' column shows the change in VO2peak from the beginning to the end of the intervention, providing a measure of how much the exercise program improved cardiorespiratory fitness.
Scientific Validity
  • Detailed Intervention Description: The table provides a detailed description of the exercise interventions, including frequency, intensity, duration, and mode of exercise. This level of detail is crucial for replicating the interventions and understanding the specific components that may have contributed to the observed effects.
  • Intensity Monitoring and Achievement: The table includes information on both intended and achieved exercise intensity, as well as the methods used for intensity monitoring. This is important for assessing the fidelity of the interventions and understanding the actual intensity experienced by participants.
  • VO2peak Measurement: The table specifies the methods used for measuring VO2peak, which is a key outcome measure in this study. The inclusion of pre- and post-intervention VO2peak values allows for an assessment of the effectiveness of the interventions in improving cardiorespiratory fitness.
  • Attendance Reporting: The table reports attendance rates for each study, which is an important indicator of participant adherence to the interventions. High attendance rates suggest that the interventions were feasible and well-tolerated by participants.
  • MET Calculation: The inclusion of weekly minutes and METs (metabolic equivalents) provides a standardized measure of exercise volume, allowing for comparisons across studies that used different exercise protocols.
Communication
  • Comprehensive Overview: The table provides a comprehensive overview of the exercise interventions and testing methods, allowing readers to quickly grasp the key characteristics of each study.
  • Clear and Organized Structure: The table is well-organized and easy to read, with clear column headings and a logical arrangement of information.
  • Use of Abbreviations: The table uses a number of abbreviations, which may make it challenging for readers who are not familiar with exercise science terminology. However, the abbreviations are generally standard within the field and are defined in the footnotes.
  • Footnotes for Clarification: The table includes extensive footnotes that provide additional information and clarification, particularly regarding the calculation of METs and the sources of information. These footnotes enhance transparency and help to ensure that the data is interpreted correctly.
  • Visual Complexity: The table is quite visually complex, with a large amount of information packed into a relatively small space. This may make it difficult for some readers to navigate and digest the information.

RESULTS

Key Aspects

Strengths

Suggestions for Improvement

Non-Text Elements

FIGURE 2 Pooled effects of aerobic exercise compared with non-exercising...
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FIGURE 2 Pooled effects of aerobic exercise compared with non-exercising control on VO₂peak.

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FIGURE 2 Pooled effects of aerobic exercise compared with non-exercising control on VO₂peak.
First Reference in Text
four studies 48-51 also incorporated a non-exercising control group and were accordingly included in the overall meta- analysis, albeit separately (Figure 2).
Description
  • Type of Figure: This is a forest plot, which is a graphical display commonly used in meta-analyses to show the results of individual studies and the overall pooled effect. A meta-analysis, as explained earlier, is a statistical method that combines the results of multiple studies to get a more precise estimate of an effect. In this case, it's the effect of aerobic exercise on VO₂peak, which is a measure of cardiorespiratory fitness.
  • Study Comparisons: The plot compares the effects of aerobic exercise against a non-exercising control group. This means that some people in the studies were doing aerobic exercise, while others were not, and the researchers measured the difference in their VO₂peak. This allows us to see if exercise had a positive, negative, or no effect compared to not exercising.
  • Individual Study Data: Each row in the plot represents a different study, identified by the first author's last name and the year of publication (e.g., 'Dipietro et al. (2006a)'). For each study, there is a square whose size reflects the weight of that study in the meta-analysis. Studies with larger sample sizes, and thus more precise estimates, generally have larger squares and contribute more to the overall result. The horizontal line extending from each square represents the 95% confidence interval (CI) for that study's result. The CI gives a range of values within which we can be reasonably sure the true effect lies. A narrower CI indicates a more precise estimate.
  • Pooled Effects: The diamonds in the plot represent the pooled effects, which are the overall results of the meta-analysis. There are separate pooled effects for studies using moderate-intensity exercise ('Mod.'), high-intensity exercise ('High'), and an overall pooled effect ('Pooled overall'). The location of the diamond shows the average effect size, and the width of the diamond represents the 95% CI for the pooled effect.
  • Effect Size Measure: The plot uses 'Hedges's g' as the measure of effect size. Effect size is a standardized way of quantifying the difference between two groups, in this case, the exercise group and the control group. Hedges's g is a specific type of effect size that is often used in meta-analyses because it corrects for bias in small sample sizes. A positive Hedges's g indicates that exercise had a positive effect on VO₂peak compared to the control group, while a negative value would indicate a negative effect.
  • Numerical Scale: The horizontal axis at the bottom of the plot shows the numerical scale for Hedges's g. The vertical dashed line at 0 represents no effect, meaning that exercise and control groups had the same VO₂peak. Values to the right of this line indicate a positive effect of exercise, and values to the left indicate a negative effect.
  • Interpretation of Results: By looking at the position of the squares and diamonds relative to the zero line, we can see whether exercise had a statistically significant effect on VO₂peak. If the CI for a study or the pooled effect does not cross the zero line, the result is considered statistically significant, meaning that it is unlikely to have occurred by chance.
Scientific Validity
  • Appropriate Use of Forest Plot: The use of a forest plot is appropriate for visualizing the results of a meta-analysis. It allows for a clear comparison of individual study results and the overall pooled effect.
  • Inclusion of Non-Exercising Control: The inclusion of studies with a non-exercising control group is crucial for establishing the specific effect of aerobic exercise on VO₂peak, as it provides a baseline for comparison.
  • Weighting of Studies: The plot appears to weight studies appropriately, with larger squares representing studies with more statistical weight (likely due to larger sample sizes). This ensures that studies with more precise estimates contribute more to the overall pooled effect.
  • Use of Hedges's g: The use of Hedges's g is appropriate for a meta-analysis, as it is a standardized measure of effect size that accounts for potential bias in small sample sizes.
  • Reporting of Confidence Intervals: The plot reports 95% confidence intervals for both individual studies and pooled effects, which is essential for assessing the precision and statistical significance of the results.
Communication
  • Clear Labeling: The plot is clearly labeled, with a descriptive title, clear axis labels, and labels for each study and pooled effect. The use of abbreviations ('Mod.' and 'High') is appropriate and consistent with the paper's terminology.
  • Visual Clarity: The plot is visually clear and easy to understand, with a simple and uncluttered design. The use of different symbols (squares and diamonds) and colors helps to distinguish between individual studies and pooled effects.
  • Numerical Scale and Zero Line: The numerical scale and zero line are clearly marked, making it easy to interpret the magnitude and direction of the effects.
  • Study Identification: Each study is clearly identified by the first author's last name and year of publication, allowing for easy cross-referencing with the paper's references.
  • Legend and Footnotes: Although not shown in the provided text, it can be assumed that the figure has a legend or footnotes that provide further explanation of the symbols, abbreviations, and statistical methods used. This is important for ensuring that the plot can be understood by readers who may not be familiar with forest plots or meta-analysis.
FIGURE 3 Pooled effects of moderate- versus high-intensity aerobic exercise on...
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FIGURE 3 Pooled effects of moderate- versus high-intensity aerobic exercise on VO₂peak.

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FIGURE 3 Pooled effects of moderate- versus high-intensity aerobic exercise on VO₂peak.
First Reference in Text
Seven studies41,42,47-51 presented results for both moderate- and high-intensity groups, making them eligible for inclusion in the meta-analysis comparison be- tween these intensity categories (Figure 3).
Description
  • Type of Figure: This is another forest plot, similar to Figure 2. Forest plots are used to visually summarize the results of multiple studies in a meta-analysis. In this case, the plot is comparing the effects of moderate-intensity aerobic exercise versus high-intensity aerobic exercise on VO₂peak. This is a more specific comparison than in Figure 2, which compared exercise to a non-exercising control.
  • Study Comparisons: The plot directly compares head-to-head the results from studies that included both a moderate-intensity exercise group and a high-intensity exercise group. This allows us to see which type of exercise had a greater effect on VO₂peak within the same study population. It is comparing apples to apples, so to speak, in terms of exercise intensity.
  • Individual Study Data: Each row represents a single study, again identified by the first author's last name and year of publication. The square represents the effect size for that study, with the size of the square indicating the study's weight in the meta-analysis (larger studies, which are more reliable, get larger squares). The horizontal line through each square is the 95% confidence interval (CI), which gives us a range of where the true effect likely falls.
  • Pooled Effect: The diamond at the bottom of the plot represents the pooled effect, which is the overall result of combining all the individual studies in the meta-analysis. It shows the average difference between moderate- and high-intensity exercise across all included studies. The width of the diamond represents the 95% CI for the pooled effect.
  • Effect Size Measure: The plot uses 'Hedges's g' as the measure of effect size, which is a standardized way of comparing the difference between two groups (in this case, moderate vs. high intensity). A positive Hedges's g would mean that moderate-intensity exercise had a larger effect on VO₂peak, while a negative value would favor high-intensity exercise. A value of zero means no difference between the two.
  • Numerical Scale: The horizontal axis at the bottom shows the numerical scale for Hedges's g. The vertical dashed line at zero represents no difference between moderate- and high-intensity exercise. Values to the right of this line would indicate that moderate-intensity is more effective, and values to the left would indicate that high-intensity is more effective.
  • Interpretation of Results: By examining the position of the squares and the diamond relative to the zero line, we can determine whether there is a statistically significant difference between moderate- and high-intensity exercise. If the CI for a study or the pooled effect does not cross the zero line, the difference is considered statistically significant, meaning it's unlikely to be due to random chance.
Scientific Validity
  • Appropriate Comparison: Comparing moderate- versus high-intensity exercise directly within the same studies is a scientifically sound approach to determine which intensity is more effective for improving VO₂peak. This controls for potential confounding factors that might exist between different study populations.
  • Eligibility Criteria: The reference text states that seven studies were eligible for this comparison because they included both moderate- and high-intensity groups. This suggests that clear eligibility criteria were used, which is important for ensuring the validity of the meta-analysis.
  • Use of Forest Plot: The use of a forest plot is appropriate for visualizing the results of this meta-analysis, as it allows for a clear comparison of individual study results and the overall pooled effect.
  • Weighting of Studies: The plot appears to weight studies appropriately, as indicated by the varying sizes of the squares. Larger squares represent studies with more statistical weight (likely due to larger sample sizes), which is important for ensuring that the pooled effect is not unduly influenced by smaller, less precise studies.
  • Use of Hedges's g: The use of Hedges's g is appropriate for this type of meta-analysis, as it provides a standardized measure of effect size that is suitable for comparing different interventions.
Communication
  • Clear Labeling: The plot is clearly labeled, with a descriptive title, clear axis labels, and labels for each study. The use of abbreviations ('Mod.' and 'High') is consistent with the paper's terminology.
  • Visual Clarity: The plot is visually clear and relatively easy to understand, with a simple and uncluttered design. The use of different symbols (squares and diamond) helps to distinguish between individual studies and the pooled effect.
  • Numerical Scale and Zero Line: The numerical scale and zero line are clearly marked, making it easy to interpret the magnitude and direction of the effects.
  • Study Identification: Each study is clearly identified by the first author's last name and year of publication, which allows for easy cross-referencing with the paper's references.
  • Limited Number of Studies: The plot includes a relatively small number of studies (7), which may limit the generalizability of the findings. However, this is acknowledged in the reference text and is a limitation of the available research rather than a communication issue.
TABLE 3 Study quality assessment of included studies using TESTEX scale.
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