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.
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.
The abstract clearly outlines a systematic approach to searching multiple relevant databases, ensuring a thorough review of the existing literature.
The study focuses on V̇O2peak as the primary outcome, a well-established and objective measure of cardiorespiratory fitness.
The abstract specifies the inclusion criteria, including the number of studies, participants, and division into intensity groups, providing a clear picture of the study population.
The abstract succinctly summarizes the main findings from the meta-regression and comparison of intensity groups, highlighting the lack of significant differences.
The abstract concludes by challenging the superiority of high-intensity exercise and emphasizes the importance of regular aerobic exercise, regardless of intensity, for improving CRF in older adults.
This high-impact improvement would enhance the study's methodological rigor and transparency. The Abstract section particularly needs this detail as it is the first point of contact readers have with the study's methodology and its impact on the main findings.
Implementation: Specifically mention how exercise volume was accounted for or standardized across the studies. For example, "...taking into account the completed exercise volume, quantified as MET-minutes per week." or "...after standardizing for exercise volume using a MET-based calculation."
This medium-impact improvement would strengthen the abstract's presentation of results and provide a more precise understanding of the findings. As the Abstract is often the most-read section, including key statistical values here would significantly improve its informativeness.
Implementation: Include the specific statistical values (e.g., β, Hedges' g, and their confidence intervals) when reporting the main findings. For example, "Meta-regression analysis showed a moderate, but not significant, relationship between exercise intensity and improvements in V̇O2peak (β = 0.31, 95% CI = [−0.04; 0.67])."
This medium-impact improvement would enhance the abstract's contribution to the field by providing clearer direction for future research. The Abstract section is an ideal place to briefly outline the next steps in this area of research.
Implementation: Expand slightly on the recommendation for future RCTs. For example, "Future RCTs should prioritize valid and reliable methodologies for monitoring and reporting exercise volume and adherence among older adults, potentially incorporating qualitative methods to explore participant experiences."
The introduction effectively establishes the significance of the research problem by highlighting the global aging population and the associated decline in cardiorespiratory fitness (CRF). It clearly defines CRF and its importance for healthy aging.
The introduction identifies a clear research gap by pointing out the lack of studies that have investigated the impact of exercise intensity on CRF in older adults while accounting for exercise volume.
The introduction clearly states the aim of the study, which is to compare the effects of moderate- versus high-intensity aerobic exercise on CRF in older adults, considering exercise volume.
The introduction provides a logical flow of information, starting with the broader context of aging and CRF, then narrowing down to the specific research problem and the study's aim. It effectively connects the research to existing literature and guidelines.
This high-impact improvement would strengthen the introduction by providing a more detailed justification for the specific focus on exercise intensity. As the introduction sets the stage for the entire study, elaborating on this aspect would enhance the reader's understanding of the research's significance and novelty.
Implementation: Provide a more in-depth explanation of why exercise intensity is a crucial factor to investigate, beyond just mentioning its role in the FITT principle. For example, discuss how different intensities might differentially affect physiological adaptations or adherence in older adults. Briefly touch upon existing controversies or gaps in the literature regarding optimal intensity for this population.
This medium-impact improvement would enhance the introduction by briefly hinting at the potential implications of the study's findings. While the discussion section will delve deeper, providing a glimpse of the potential impact in the introduction can further engage the reader and highlight the study's relevance.
Implementation: Add a sentence or two suggesting how the findings could inform exercise prescription guidelines or public health recommendations for older adults. For example, mention that the results could help tailor exercise programs to maximize CRF benefits while considering individual preferences and limitations.
This medium-impact improvement would enhance the introduction by explicitly stating how accounting for exercise volume adds novelty to the study. Since this is a key distinguishing feature, emphasizing its significance in the introduction will further solidify the study's contribution to the field.
Implementation: Clearly state that while previous studies may have compared exercise intensities, this study is unique in its approach of systematically accounting for total exercise volume. Briefly explain why this is important, such as minimizing confounding effects and providing a more accurate comparison of intensity-related effects.
The study employs a thorough and systematic search strategy adhering to the PRISMA guidelines, ensuring a comprehensive review of the relevant literature.
The study defines clear and specific inclusion and exclusion criteria, ensuring that only relevant studies are included in the analysis.
The study employs a rigorous process for data extraction and quality assessment, involving multiple independent reviewers and using a validated tool (TESTEX) to assess the risk of bias.
The study utilizes a detailed and appropriate statistical analysis plan, including meta-regression and subgroup analyses, to explore the relationship between exercise intensity and CRF improvements.
This high-impact improvement would enhance the study's methodological rigor and transparency. The Methods section is crucial for understanding how data limitations were addressed, which directly impacts the reliability of the findings.
Implementation: Specifically describe the approach taken when encountering missing data, such as standard deviations or other parameters needed for effect size calculations. For example, state whether attempts were made to contact study authors for missing data, or if any imputation methods were used. If no specific method was used, explicitly state that studies with missing data were excluded from certain analyses.
This high-impact improvement would significantly strengthen the study's methodology by providing a more detailed explanation of how exercise volume was calculated and standardized across different studies. As a central aspect of the study's novelty and a key factor in the meta-regression analysis, a more thorough description in the Methods section is essential for ensuring reproducibility and allowing readers to fully understand the nuances of this critical variable.
Implementation: Provide a more detailed explanation of the formula used to calculate weekly exercise volume, including a step-by-step breakdown of each component (achieved exercise intensity, session duration, frequency, and attendance). Include specific examples of how MET values were assigned to different exercise intensities and modalities, particularly for studies that did not explicitly report MET values. Consider adding a supplementary table that provides the calculated exercise volume for each included study, along with the specific parameters used in the calculation.
This medium-impact improvement would strengthen the study's methodological rigor by providing a clear justification for the use of a random-effects model in the meta-analysis. As the choice of statistical model can influence the results and interpretation of a meta-analysis, explicitly stating the rationale in the Methods section is important for transparency and allows readers to assess the appropriateness of the chosen approach.
Implementation: Briefly explain why a random-effects model was chosen over a fixed-effect model. This could involve mentioning the anticipated heterogeneity between studies due to variations in populations, interventions, or outcome measurements. For example, state that a random-effects model was used because it accounts for both within-study and between-study variability, making it more suitable when heterogeneity is expected.
Figure 1 Flowchart of the systematic review and meta-analysis according to the PRISMA guidelines. Updated search: 09.05.2023.
TABLE 2 Characteristics of the aerobic exercise interventions and methods for testing cardiorespiratory fitness.
The Results section provides a thorough overview of the included studies, participant demographics, and exercise intervention characteristics, offering a clear context for interpreting the findings.
The section clearly presents the results of the meta-regression analysis, including the effect size, confidence interval, and z-value, allowing for a proper understanding of the relationship between exercise intensity and VO2peak improvements.
The section provides a detailed account of the subgroup analyses, exploring the influence of various factors on VO2peak improvements and offering valuable insights into the potential moderators of the exercise-VO2peak relationship.
The section includes the results of the risk of bias assessment using the TESTEX scale, providing an evaluation of the methodological quality of the included studies.
This high-impact improvement would enhance the transparency and methodological rigor of the Results section. As this section is crucial for presenting the findings and justifying the analytical approach, providing a more detailed explanation for excluding studies from the meta-analysis would allow readers to better understand the selection process and its potential impact on the overall results.
Implementation: Provide a more detailed explanation of the reasons for excluding eight studies from the overall meta-analysis due to the absence of a non-exercising control group. Elaborate on the decision to exclude four studies that compared similar intensity groups, specifying how these comparisons differed from the main comparison of interest (moderate- vs. high-intensity). Consider adding a supplementary table that lists the excluded studies and the specific reasons for their exclusion.
This medium-impact improvement would enhance the interpretability of the Results section by providing more context for the non-significant findings. As this section is where the main results are presented, offering potential explanations for the lack of statistical significance in certain analyses would help readers better understand the nuances of the findings and their implications.
Implementation: When reporting non-significant findings, such as the relationship between exercise intensity and VO2peak improvements in the meta-regression analysis, briefly discuss potential reasons for the lack of statistical significance. For example, mention the possibility of insufficient statistical power due to the limited number of studies or the presence of heterogeneity among the included studies. Consider discussing the clinical significance of the findings, even if they did not reach statistical significance.
This medium-impact improvement would enhance the Results section by providing a more in-depth discussion of the heterogeneity findings. As heterogeneity can significantly impact the interpretation of meta-analysis results, elaborating on its potential sources and implications in this section would provide readers with a more nuanced understanding of the study's findings and their limitations.
Implementation: Expand on the discussion of heterogeneity beyond simply reporting the I² and T² values. Discuss potential sources of heterogeneity, such as differences in participant characteristics, exercise protocols, or outcome measurement methods. Briefly explain how heterogeneity might have affected the results and their interpretation. Consider mentioning the use of a random-effects model as a way to account for heterogeneity in the analysis.
FIGURE 2 Pooled effects of aerobic exercise compared with non-exercising control on VO₂peak.
FIGURE 3 Pooled effects of moderate- versus high-intensity aerobic exercise on VO₂peak.