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• January 10, 2024

The Impact of Physical Fitness on Public Health: A Systematic Review Protocol

Table Of Content

1. Introduction 3

1.1 Background 3

1.2 Rationale 4

1.3 Objectives 4

2. Methods 6

2.1 Protocol and Registration 6

2.2 Eligibility Criteria 6

2.2.1 Study designs 6

2.2.2 Participants/Population 7

2.2.3 Interventions 7

2.2.4 Comparators 7

2.2.5 Outcomes 8

2.2.6 Timing 8

2.2.7 Settings 9

2.3 Information Sources 9

2.4 Search Strategy 10

2.5 Study Selection 11

2.6 Data Extraction 11

3. Results 13

3.1 Study Selection 13

3.2 Study Characteristics 13

3.3 Risk of Bias Within Studies 14

3.4 Synthesis of Results 15

Quantitative Synthesis 15

Qualitative Synthesis 15

4. Discussion 16

4.1 Summary of Evidence 16

4.2 Limitations 17

4.3 Implications for Practice and Research 18

Conclusions 19

References 20

1. Introduction

1.1 Background

Regular physical activity is associated with a markedly lower risk of heart disease, stroke, type 2 diabetes, various cancers and all-cause mortality (Reiner et al., 2013). Yet it is estimated that as many as 31% of adults worldwide fail to meet recommended activity levels, with concerning declines observed over the past decade (Guthold et al., 2018). As displayed in Figure 1, regions like the Americas and Eastern Mediterranean have particularly high rates of physical inactivity exceeding 35% of adults (Guthold et al., 2018). Even where gains had been made previously, progress appears to be reversing – high-income Western nations that close to 50% reductions in physical inactivity from 2001 to 2016 are now seeing stabilization or worsening trends (Guthold et al., 2020). Simultaneously, the health and economic burdens imposed by lack of activity remain staggering, responsible for up to 10% of annual healthcare expenditures in some national contexts (Ding et al., 2021).

(Source: drroopesh, 2018)

Figure 1. Prevalence of insufficient activity among adults by WHO world region

Within this landscape, physical fitness has received renewed attention for its potential as a vital indicator of current and future health status at both individual and population levels (Ortega et al., 2021). Indeed higher fitness levels relating to attributes like cardiovascular capacity confer a substantially lower risk of mortality and development of chronic diseases even among those failing to meet formal physical activity recommendations (Bell et al., 2020). This indicates fitness represents a concrete modifiable determinant of health, rather than a simple proxy for generalized activity behaviors. There are also suggestions that health gains associated with enhanced fitness could be more pronounced than those linked solely with shifts in activity. For example, marked reductions are observed in hypertension prevalence with improved fitness despite activity levels (Liguori et al., 2018).

Yet fitness remains under-evaluated within public health initiatives which have centered largely on physical activity, while fitness tracking has been driven predominantly via commercial entities like smart device companies without intersections with health systems (Stanton et al., 2021). Opportunities likely exist to integrate fitness assessments, targeted interventions and population monitoring into mainstream public health practice given the positive implications for chronic disease prevention and supporting healthy longevity.

1.2 Rationale

Existing literature syntheses have focused squarely on promoting physical activity rather than fitness outcomes per se. For example, the 2018 Cochrane Review of interventions targeting walking evaluated participation rates, step counts and various activity metrics without fitness linkages (Richards et al., 2018). While activity should assuredly remain a central emphasis in public health efforts, sufficient evidence has accrued regarding the health-enhancing effects of fitness (Ortega et al., 2021) to justify dedicated attention towards fitness-enhancing initiatives. This systematic review addressing relationships between fitness-focused programs and outcomes across populations will help address this gap.

The review is timely and essential to inform coordinated policy and programming given that most public health messaging, guidelines and invested funding revolve around physical activity goals often without specific fitness considerations. Elucidating effective interventions capable of bolstering fitness has implications for strategic planning and resource allocation for non-communicable disease prevention. The review also has potential to guide technological innovation as consumer wearables and fitness applications proliferate rapidly, constituting an underexploited avenue for supporting public health aims.

1.3 Objectives

This systematic review will pursue the following objectives:

● Evaluate associations between physical fitness levels and health outcomes including mortality, cardiovascular disease, cancer, mental health, healthcare utilization and adverse event measures

● Appraise the effectiveness of structured initiatives explicitly intended to enhance physical fitness across populations on health-related outcomes

● Identify and synthesize evidence regarding factors influencing adoption of and adherence to physical fitness assessment and intervention approaches

● Outline implications for public health policy, practice and programming based on collated international data around fitness and health

In summary, the planned review will assemble rigorous evidence clarifying pathways between an important but often overlooked health determinant in physical fitness and relevant public health outcomes while delineating practical strategies translatable to regional and national scale.

2. Methods

2.1 Protocol and Registration

This protocol is structured according to the preferred reporting items for systematic reviews (PRISMA-P) guidance (Moher et al., 2015). The protocol will be registered with PROSPERO following stakeholder review. Any amendments during the review process will be documented.

2.2 Eligibility Criteria

2.2.1 Study designs

This systematic review will utilize broad eligibility criteria to capture the breadth of literature around physical fitness interventions and their impacts on public health outcomes. As shown in Table 1, a wide range of study designs will be included beyond just randomized trials. For example, Larsen et al. (2022) included experimental and quasi-experimental studies with control groups in their systematic review and meta-analysis of physical activity monitors. Observational data around factors influencing adoption and adherence will also be relevant.

Table 1. Study Designs Included in Related Systematic Reviews

2.2.2 Participants/Population

The review will focus on adult populations aged 18+ years. As highlighted by Medrano-Ureña et al. (2020), few studies have evaluated physical fitness among general adult populations, with most targeting clinical groups. By specifying adults aged 18+ years, findings related to community-based public health strategies will be emphasized rather than clinical interventions.

2.2.3 Interventions

A broad conception of physical fitness will be utilized spanning cardio, strength, flexibility, and motor fitness measures. This aligns with validated models like that proposed by Caspersen et al. (1985). Exercise modalities will include those recommended within physical activity guidelines like aerobic and muscle strengthening activities (Piercy et al., 2018). As shown in Table 2, common interventions have included instructor-led exercise classes, provision of home equipment like treadmills, and technology tools like fitness trackers. Multicomponent programs will be eligible given evidence that combined dietary and exercise initiatives could yield greater adherence than exercise alone (Johns et al., 2014).

Table 2. Categories of Interventions Used in Related Reviews

2.2.4 Comparators

Relevant comparators include inactive controls, standard care, or alternative types of fitness programming receive by comparison groups. Medrano-Ureña et al. (2020) highlighted the heterogeneity of comparators as a barrier to meta-analysis, spanning placebo controls, usual fitness routines, or other exercise regimens. Table 3 summarizes comparator groups included in related systematic reviews.

Table 3. Categories of Comparators Used in Related Reviews

2.2.5 Outcomes

A breadth of public health outcomes will be incorporated spanning mortality, cardiovascular health, cancer, mental health, healthcare utilization, adverse events, and intervention adoption/adherence. Collection of data on negative health impacts will be important given evidence that excessive amounts of exercise can increase upper respiratory tract infection risk and musculoskeletal injury rates (Nieman, 1994). Assessing adoption and adherence will also be key; Tong et al. (2022) found that use of fitness apps declines sharply over time, necessitating a focus on long-term maintenance.

2.2.6 Timing

Requiring at least 12 weeks follow-up aligns with guidance on appropriate timeframes to assess intervention efficacy and emphasizes maintenance rather than solely adoption outcomes (Kahlert & Unyi-Reicherz, 2016). Recent reviews have imposed follow-up periods ranging from 4 weeks (Meyer et al., 2020) up to 2 years (Rollo et al., 2016).

2.2.7 Settings

Finally, no restrictions will be imposed based on setting. This will enable synthesis of evidence from diverse contexts like workplaces, community spaces, and clinical settings. Comparative data around adoption rates and participation across settings will be informative.

In summary, broad eligibility criteria have been selected to enable capture of real-world evidence on the relationships between fitness initiatives and public health outcomes across a variety of populations, contexts and study designs.

2.3 Information Sources

A comprehensive set of databases will be searched reflecting the multidisciplinary nature of research on physical fitness interventions, including specialized indexes like SPORTDiscus along with major biomedical literature databases. As displayed in Table 1, the number of unique eligible papers identified from different databases can vary substantially depending on the focus of the search. Ensuring wide coverage is therefore important to avoid missing relevant literature.

Table 4. Unique Eligible Papers Identified by Database Searched

Grey literature searches will supplement indexed literature by capturing documents like policy reports, program evaluations, or theses not published in academic journals. Grey literature constituted 12% of sources in the review by Warburton and Bredin (2017) and revealed insights around barriers to adoption of physical activity interventions.

No language, publication year or publication status restrictions will be imposed. The first study demonstrating the mortality benefits of cardiorespiratory fitness was published in the 1970s (Blair et al., 1996), underscoring the need for historical coverage. Further, Larsen et al. (2022) included eligible non-English papers, enabling unique data from seven additional trials to be incorporated.

2.4 Search Strategy

Both controlled vocabulary (Medical Subject Headings) as well as keywords will be applied to capture relevant literature. Asdisplayed in Figure 2, the combination of title/abstract keywords with MeSH terms yielded higher recall than either approach alone in an related search. Input from an information specialist will optimize syntax and strategies for each database.

(Source: Nair, 2020)

Figure 2. Unique records retrieved from keyword vs. MeSH based search strategies

2.5 Study Selection

As summarized in Table 2, two reviewers will independently screen all titles/abstracts and full texts to minimize bias in study selection, resolving conflicts via discussion or third party adjudication. Usage of Covidence software will enable tracking of reviewer decisions and help streamline collaboration.

Table 5. Dual Reviewer Study Selection Process

2.6 Data Extraction

Standardized data collection forms will capture key descriptive, methodological and outcome data needed to assess study quality and synthesize evidence:

● Study identifiers and design

● Participant characteristics

● Details of interventions and controls

● Specific measurement tools utilized

● Available outcome data and effect estimates

Dual extraction helps minimize errors, with McDonald et al. (2021) finding that lone data extractors missed important information in 30% of reviewed papers. In summary, the planned search approach leverages available evidence while the selection methods and extraction process incorporate safeguards against bias and error.

3. Results

3.1 Study Selection

The study selection process will be summarized via a PRISMA flow chart depicting the number of papers identified, screened, eligibility assessed, included and excluded (Moher et al., 2009).

Associated tables will describe key study characteristics retained for synthesis including author details, publication year, country context, study design, methodological features, and pertinent participant demographics. Table 1 displays the categories of data that will be tabulated to profile retained studies.

Table 6. Summary of Study Characteristics

3.2 Study Characteristics

It is projected that included studies are likely to cluster into subgroups based on common intervention approaches, participant cohorts, settings, or research methodologies. For example, there may be distinguishable sets of randomized trials focused on provision of wearables technologies versus structured exercise classes as displayed hypothetically in Figure 3. Descriptive summaries will look to categorize retained papers into logical themes.

(Source: Dr. Cath, 2019)

Figure 3. Example categorization of studies by intervention type

3.3 Risk of Bias Within Studies

The profile of internal validity for included literature will be summarized by tabulating the overall frequency of studies rated as having low, moderate or high risk of bias both in aggregate terms and within specific domains like deviations from intended interventions or missing outcome data. Table 7 provides an illustrative example using Cochrane Risk of Bias 2 judgments. Justifications will describe sources of major biases identified like lack of blinding in trials or failure to appropriately match controls in observational analyses.

Table 7. Hypothetical Risk of Bias Assessments

3.4 Synthesis of Results

Quantitative Synthesis

If sufficiently homogeneous with available aggregate outcome data, random-effects meta-analysis will be applied to estimate pooled intervention effects. Hypothetical forest plots are presented for all-cause mortality and cardiovascular event rates. Parameters summarized will include ratios of relative risks, weighted mean differences for continuous outcomes, 95% confidence intervals, measures of consistency across studies (I2 and T2 statistics) and tests for reporting biases like funnel plots. Subgroup analyses will explore heterogeneity sources.

Qualitative Synthesis

However, narrative qualitative synthesis is likely required for many outcomes. In this case, evidence will be evaluated across critical domains as demonstrated in the conceptual framework. Summary paragraphs and evidence profile tables will synthesize judgments on considerastions like outcome relevance, applicability of context, adequacy of durations assessed, precision of results and overall certainty.

4. Discussion

4.1 Summary of Evidence

While collated study findings will be outlined in the completed review, this section summarizes key relationships and effectiveness data expected to emerge between physical fitness and health outcomes. Meta-analyses demonstrate clear mortality benefits from even modest fitness improvements equivalent to moving from unfit to moderately fit categories based on VO2 max levels (Kodama et al., 2009). Further, emerging research indicates that higher fitness levels could eliminate the increased cardiovascular risks associated with obesity (Barry et al., 2014). Table 1 displays pooled risk reductions from related meta-analyses for various public health outcomes, highlighting the extensive morbidity and mortality benefits potentially attributable to enhanced fitness.

Table 8. Risk Reductions Associated with Higher Fitness Levels

Regarding influential factors, data consistently demonstrate substantially higher adoption and adherence among program participants offered financial incentives or free access to fitness facilities (Mitchell et al., 2013; Pavey et al., 2011). Convenience and social support also appear significant; Laranjo et al. (2020) found 50% increased odds of persistence with fitness apps incorporating social networking components. Environmental dynamics likewise seem to exert effects; walkability, density of fitness resources, and proximity to parks correlate with activity levels at a neighborhood level (Sallis et al., 2016).

Effective intervention strategies suitable for large-scale implementation could include referral schemes integrating fitness assessments and prescriptions within primary care (Pavey et al., 2011), population-level health behavior change messaging emphasizing functional fitness benefits (Blue et al., 2016), and partnerships with fitness companies enabling subsidized community facility memberships (Gilbert et al., 2022).

However, limitations of current literature include heterogeneity in measurement of exposures and outcomes, lack of long-term follow-up, inadequate reporting of intervention components, and availability of real-world effectiveness data at scale. Targeted research efforts are needed addressing these gaps.

4.2 Limitations

Despite efforts to ensure a rigorous methodology, all reviews have inherent limitations worth acknowledging transparently as these could influence interpretation of collated evidence.

Firstly, heterogeneity across studies assessing multifaceted concepts like physical fitness and diverse health outcomes is anticipated. As reported in Table 2, the degree of heterogeneity as measured by the I2 statistic ranged from moderate (50-75%) to high (>75%) even within pooled analyses focused on singular outcomes like myocardial infarction or aerobic capacity (Goldsby et al., 2020; Pandey et al., 2015). Such heterogeneity could necessitate reliance on less precise random effects models and narrative qualitative synthesis approaches.

Table 9. Heterogeneity Levels in Related Meta-Analyses

Publication bias skewed towards reporting of favorable fitness intervention results is also plausible and difficult to fully exclude, similar to other domains (Dwan et al., 2013). It is recognized that the exclusion of unpublished data due to feasibility constraints may contribute to overestimations of effect sizes if negative findings remain unpublished. Analyses will seek to appraise potential reporting biases.

Finally, human errors during study selection, data extraction and appraisal cannot be ruled out. However, this will be minimized via usage of dual reviewers and consensus resolution approaches to reduce likelihood of mistakes, omissions or subjectivity influencing review processes. Any issues encountered will be transparently reported to qualify synthesized results.

4.3 Implications for Practice and Research

The aggregated evidence has the potential to meaningfully inform policy, practice and programming related to utilizing fitness-oriented strategies for public health benefit. Review findings will help delineate effective intervention components and implementation models suitable for population-level dissemination across community and healthcare settings. Strategies with lower cost burdens and resource requirements could be accentuated for integration within scaled prevention efforts.

For example, study data might demonstrate meaningful weight reductions achievable via access to exercise equipment during office hours (DeJoy et al., 2016) or reduced short-term hospital readmission rates through pre-discharge functional assessments and prescribed exercise regimens (Khamis et al., 2018). Positive findings could then directly influence development of workplace wellness schemes and hospital discharge planning procedures to better support fitness.

Likewise, if factors related to adoption and adherence are illuminated, such as preferences for mobile versus face-to-face fitness resources (McCallum et al., 2019) or stepped dose-response relationships between program intensity and drop-out risks (Kerse et al., 2020), then population messaging and program structures could be optimized accordingly.

Research implications will center on addressing limitations like short-term reach of studies  68% of evaluations spanned under 1 year, constraining understandings of long-term impacts and sustainability (Lambert et al., 2018). More assessments of cost effectiveness and implementation barriers at scale will also be warranted. Targeting identified evidence gaps through coordinated funding schemes oriented around translation of fitness initiatives into applied public health practice is justified and aligned to consensus research priorities in this domain (Reis et al., 2016).

In summary, aggregated data could inform promotion of evidence-based, scalable fitness strategies integrated into multilevel efforts to curb rising chronic disease burdens worldwide.

Conclusions

Declining physical activity and fitness globally demands innovative public health strategies involving interventions targeting fitness directly. This systematic review will synthesize literature regarding relationships between physical fitness and health while outlining effective, scalable initiatives suitable for implementation within community and clinical settings. The review will also reveal opportunities to enhance future research efforts in this domain. Shared understanding of pathways linking fitness and health along with knowledge to inform policies and programs represent the intended impact of this review.

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