Metabolic syndrome (MetS) is recognized as a cluster of cardiovascular disease risk factors including waist circumference (WC), triglycerides (TG), high-density lipoprotein (HDL) cholesterol, blood pressure (BP), and blood glucose (BG).¹ Many healthcare professionals are familiar with these five criteria proposed by the National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATP 3) in 2005 for diagnosing MetS.² Reducing the severity of MetS is a significant target to improve global health, as it substantially increases the risk of cardiovascular events.³

For decades, exercise intervention has been utilized for the prevention and treatment of MetS, often in conjunction with other therapies such as medication, diet, and behavior modification. An increase in cardiorespiratory fitness induced by exercise has been well-established as a protective factor against the individual risk factors that constitute MetS.⁴ Combining exercise with a proper diet is effective in resolving MetS and reducing the severity of related abnormalities.⁵ Katzmarzyk et al.⁶ investigated the efficacy of exercise training in the treatment of MetS. They found that the prevalence of MetS, as defined by NCEP-ATP 3 criteria, was 16.9% in a sample of apparently healthy participants (105 out of 621) and that 30.5% of the 105 participants were no longer classified as having MetS after the training. Ostman et al.⁷ conducted a systematic review and meta-analysis on the effects of exercise training in patients with MetS. They included 16 studies with 23 intervention groups and found that all five risk factors of MetS (WC, TG, HDL, BP, and BG) showed significant improvement.

However, some studies have pointed out that previous research on the effect of exercise on MetS has revealed significant individual variability in responses to specific exercise doses.^3,8,9 This variability has been attributed to the absence of a personalized approach to exercise prescription.¹⁰ Weatherwax et al.³ compared the effects of individualized and standardized exercise regimens when analyzing changes in MetS severity. They found a significant difference only in systolic BP, with no significant differences observed among other risk factors.

While many studies have explored the effects of exercise on MetS with consideration of individual characteristics, the extent to which this individuality was considered varied across the studies. Various factors were taken into account, including age, sex, body mass index, fitness level, injuries, diseases, and diet. This study aimed to analyze the effectiveness of individualized exercise on the risk factors associated with MetS through a scoping review. This approach allows us to identify a more appropriate method for personalized exercise prescription in the context of MetS.

Through this review, a ‘randomized controlled trial (RCT)’ filter was applied and various databases from inception to March 15, 2023 were explored. The databases include Embase (http://www.embase.com/), PubMed (http://www.ncbi.nlm.nih.gov/pubmed/), EBSCO Academic Search Premier (http://search.ebscohost.com/), and Google Scholar (https://scholar.google.com/). The following keywords were utilized: “individualized exercise and metabolic syndrome,” “personalized exercise and metabolic syndrome,” and “customized exercise and metabolic syndrome.” Following the initial database searches, duplicate studies were eliminated and only English data sources were included.

This review applied Participants, Interventions, Comparisons, Outcomes, Timing of outcome measurement, Settings, and Study Design (PICOTS-SD) frameworks to clarify the inclusion criteria as follows:

Participants: adults with MetS aged 18 to 65 years.

Intervention: individualized, personalized, or customized exercise.

Comparison: standard exercise, routine care, etc.

Outcomes: WC, TG, HDL, BP, and BG.

Time: pre- and post-test.

Study design: RCT or one-group pre- and post-test.

In our initial search, a total of 1,240 studies were identified from various sources: 25 from Embase, 1,192 from PubMed, 13 from EBSCO Academic Search Premier, seven from Google Scholar, and three from other sources. In total, 606 duplicate studies were removed using the EndNote program (Thomson Reuters Co.). Two reviewers (an associate professor with a Ph.D. and an instructor with a Master’s degree) in the field of sports medicine screened the titles and abstracts of 634 studies and selected 17 studies based on the PICOTS-SD criteria. After the detailed screening according to the inclusion criteria, the full-text articles of these 17 studies were assessed for eligibility and eight studies were excluded for the following reasons: no full-text availability (n=1), improper intervention (n=1), non-English paper (n=1), and lack of originality (consensus, oral presentations, abstracts) (n=5). In the end, a total of nine studies were selected for this study (Fig. 1).

In the initial stage of study selection, two independent reviewers (HS and HC) screened titles and abstracts for eligibility. The agreement between the reviewers was assessed using the kappa statistic,¹¹ which was applied to evaluate inter-rater agreement while correcting for chance agreement. The kappa statistic (K_{A_B}) for reviewer agreement was calculated and found to be 0.735 (95% confidence interval, 0.657 to 0.813), indicating substantial agreement according to Landis and Koch’s guidelines.¹² These values also meet the criteria for good agreement per Fleiss’s guidelines.¹³

In the full-text screening stage, a different combination of reviewers (HS and HC) yielded a kappa statistic (K_{A_B}) of 0.658 (95% confidence interval, 0.211 to 0.999), again indicating substantial agreement.

This scoping review includes nine articles and their characteristics are presented in Table 1.^3,14-21 These studies were published between 2009 and 2020. Among them, six studies had both experimental and control groups, while three studies included only an experimental group. The ages of the participants in the seven studies ranged from the 40s to 50s, whereas two studies involved participants in their 20s and 30s.

In clinical cardiovascular practice, addressing exercise dosage and physical activity habits is essential. This should be done for each patient, aiming for the ultimate goal of providing individualized counseling and exercise prescriptions.²² Gronwald et al.²³ conducted a study on the perspective of dosage and response to individualized exercise prescriptions. They highlighted numerous personal factors that underscore the importance of individualization in exercise and training. These personal factors encompassed age, gender, anthropometry, genotype, psycho-physiological capacity level, health and recovery status, diet and hydration, medication and doping, hormone status, circadian rhythm, sleep, stress and coping strategies, motivation and emotions, psycho-social factors (e.g., family, school, finances), and social and cognitive activities, among others.

As is evident in the studies included in this research and numerous others, it is often challenging to simultaneously account for all personal factors. Personal factors can be broadly categorized into non-modifiable factors (e.g., sex or genotype) and modifiable factors (e.g., nutrition, social, or cognitive activities).²³ This study proposes an alternative classification of personal factors from a clinical and exercise science perspective.

(1) Fixed factors (e.g., sex or genotype)

(2) Adaptation factors (e.g., anthropometry, physical fitness level, recovery stage from injury, health status of cardiovascular disease risk factors, diet, and sleep habits)

(3) Response factors (recovery status from fatigue, diet, and sleep within 2 or 3 days, instantaneous pain)

Fixed factors align with non-modifiable factors, while adaptation and response factors encompass modifiable aspects. Psycho-cognitive and social factors were intentionally excluded to focus solely on the physical, physiological, and medical aspects. As a dosage is precisely adjusted and controlled in the field of medication, prescription of exercise and training should be carefully specified to achieve individualization.²³ Fixed factors are considered during the planning or programming stage of individualized exercise prescription, whereas response factors are adjusted during implementation. Adaptation factors are addressed in both planning and implementation.

As dosage is treated in clinical practice, exercise and physical activity should be evaluated and prescribed considering three primary attributes: intensity, duration, and frequency.²² The American College of Sports Medicine introduced the FITT-VP principle, which comprises Frequency (number of exercise sessions), Intensity (exercise difficulty), Time (duration of intervention), Type (exercise mode), Volume (total exercise amount), and Progression (gradual increase in exercise program difficulty) as key components.^24,25

Studies on cardiorespiratory fitness have demonstrated that employing a more individualized approach to exercise prescription enhances the effectiveness of exercise intervention.²⁶ Specifically, prescribing ‘exercise intensity’ based on the individual ventilatory threshold (VT) has proven more effective than using standardized relative exercise intensity metrics (e.g., % heart rate reserve).²⁷ This threshold-based model utilizes VT according to the guidelines outlined by the American Council on Exercise Integrated Fitness Training (ACE-IFT) model.²⁸

In the studies included in this research, three studies^3,15,20 applied individualized exercise intensity based on the VT. In the ACE-IFT studies, participants in the personalized group were progressively overloaded in terms of exercise time, frequency, and intensity. Comparing a personalized approach to exercise prescription with a standardized protocol may also lead to greater improvements in the clustering of cardiovascular risk factors, therefore reducing MetS severity.³

In most studies focusing on individualized exercise for MetS, the exercise prescription is typically provided by specialists. These specialists can include doctors, physiotherapists, professional instructors or coaches, certified kinesiologists, and professors specializing in exercise prescription. However, the communication is typically one-way, with the specialist’s recommendations taking precedence over the client’s or patient’s preferences, despite the experts’ efforts to make them personalized and customized.

One study attempted to address exercise adherence through self-regulatory behavior change techniques. However, this approach introduced a multitude of factors, including goal-setting, self-monitoring, action planning, and review of behavioral goals, along with problem-solving.²⁹ Furthermore, another study highlighted that the lack of clarity regarding effective communication behaviors in chronic pain management serves as a barrier to implementing psychologically informed physical therapy approaches, which depend on competent communication by physical therapist providers.³⁰

Given the articles mentioned above, this review suggests that applying a two-way communication approach between specialists and individuals can be more effective for individualized exercise prescriptions for MetS than the traditional one-way method. For the two-way communication approach, specialists do not specify a particular value but instead suggest an appropriate range for the FITT-VP components of exercise (Frequency, Intensity, Time, Type, Volume, and Progression). Subsequently, individuals can choose exercises within this predefined range based on their preferences.³¹ To illustrate this point, this review compared exercise prescriptions using the ACE-IFT model of the conventional one-way communication approach with a new sample model employing a two-way communication approach (Fig. 2).³² In the new sample model, specialists defined a range of exercise time during the first 4 weeks, allowing individuals to choose one of three exercise times each week. This flexibility enables individuals to select an exercise time based on their preference, considering both their physical and psychological conditioning, as specialists prescribed an appropriate range of exercise time tailored to personal factors. The subject first chooses the exercise intensity and then they decide the exercise time after the 5th week. In this two-way communication approach, individuals can adjust a wider combination of exercise intensity and time in contrast to the one-way approach. Ultimately, individuals can customize their exercise routines by adding or subtracting exercise intensity and/or time as needed. This two-way communication method can strengthen the personalized approach to exercise prescription on MetS, by reducing the impact of individual variability on the response to specific exercise prescriptions.

One of the principles in exercise prescription is individualization, which involves tailoring the exercise program to result in a customized or personalized intervention with an appropriate level of overload for a client. To be specific, factors such as the client’s health condition, physical fitness level, age, sex, and other relevant factors are taken into account when designing the frequency, intensity, time, and type of exercise.

However, often, little attention is given to the client’s preferences as an individual factor. In exercise prescription, the predominant communication method is typically one-way, with the specialist providing recommendations to the client without engaging in a two-way dialogue. The specialist makes unilateral decisions about the exercise volume, intensity, and mode, which are then communicated to the client.

Every patient has his or her unique lifestyle and preferences. Although an exercise specialist may consider these, the communication remains one-way, driven solely by the expert’s decisions. Consequently, when the individual selection of the FITT-VP components is integrated through two-way communication between the specialist and the individual, there is the potential for more effective improvements in both the severity of MetS and exercise adherence.

The authors declare no conflict of interest.

Study concept and design: KBK; analysis and interpretation of data: all authors; drafting of the manuscript: KBK; critical revision of the manuscript: KBK and HS; administrative, technical, or material support: HC and HS; and study supervision: KBK and HS.