Seungho Ryu

PURPOSE: Pooled reference data for Korean adults are limited, and Western norms may not be applicable because of ethnic differences. This study aimed to describe sex- and age-specific distributions of knee isokinetic peak torque normalized to body weight in healthy Korean adults.METHODS: Following PRISMA guidelines, PubMed, Web of Science, Google Scholar, RISS, and KISS were searched for articles published between 1990 and 2023 using combinations of the terms “isokinetic,” “muscle strength,” “muscle function,” and “Korean.” Studies were eligible if they assessed knee isokinetic strength in healthy Korean adults using Cybex or HUMAC NORM. Weighted means and 95% confidence intervals (CI) for peak torque at 60˚/s (% body weight [BW]) were calculated based on sample size.RESULTS: Thirteen studies (n=426; 245 men, 181 women) were included. In men, left knee extensor peak torque decreased from 267.5 %BW (95% CI 260.7–274.3) in those aged 20–29 years to 143.3 %BW (130.6–155.9) in those aged >60 years. In women, left knee extensor peak torque declined from 227.3 %BW (211.6–242.9) in adults aged 20–29 years to 86.7 %BW (78.7–94.6) in those aged >60 years. Flexor strength showed similar age-related declines, and men consistently exhibited higher peak torque than women.CONCLUSIONS: This study provides the first combined descriptive estimates for knee isokinetic strength in Korean adults. These values may serve as preliminary reference information for clinical assessment and exercise prescription. Results should be interpreted with caution owing to limited sample sizes in some subgroups. Large, standardized, population-based studies are needed to refine these reference standards.

OBJECTIVES The purpose of this study is to analyze whether the association between physical activity and perceived stress differs across urbanicity levels among Korean adolescents.METHODS This study utilized data from the Korea Youth Risk Behavior Survey (KYRBS), collected between 2018 and 2023. Physical activity was dichotomized based on engaging in ≥60 minutes of activity per day for seven consecutive days. Perceived stress was categorized into high and low levels based on survey responses. Urbanicity was classified into metropolitan, mid-sized city, or rural. Complex-sample logistic regression analyses were performed to assess the association between physical activity and perceived stress by urbanicity level, adjusting for age, sex, economic status, academic performance, school type, height, and weight.RESULTS A total of 322,978 adolescents were included in the analysis. The association between physical activity and perceived stress differed by urbanicity level. Adolescents in mid-sized cities who engaged in physical activity for seven consecutive days were more likely to report lower perceived stress (OR = 1.087, 95% CI = 1.035-1.142). However, no significant associations were observed among adolescents residing in metropolitan areas (OR = 1.048, 95% CI = 0.996-1.103) or rural areas (OR = 1.079, 95% CI = 0.950-1.225).CONCLUSIONS This study confirmed that the association between physical activity and perceived stress among adolescents varies by urbanicity level. Significant associations were observed only in mid-sized cities, suggesting that the stress-reducing benefits of physical activity may be influenced by contextual environmental factors. These findings highlight the need for region-specific physical activity promotion strategies to support adolescent mental health.

OBJECTIVES The purpose of this study was to examine temporal trends in physical activity and metabolic syndrome (MetS) among Korean adults, and to evaluate secular trends in the association between physical activity and MetS from 2018 to 2023.METHODS This study utilized data from the Korea National Health and Nutrition Examination Survey (KNHANES) collected between 2018 and 2023. A total of 32,639 adults aged ≥ 19 years were included. Physical activity was dichotomized based on meeting the World Health Organization guidelines (≥ 150 minutes/week of moderate to vigorous physical activity). MetS was defined according to the National Cholesterol Education Program Adult Treatment Panel III criteria with Asian-specific waist circumference cutoffs, as the presence of ≥ 3 of 5 metabolic components based on measured component values. All analyses accounted for the complex sampling design of KNHANES by applying survey weights and primary sampling units and strata. Temporal trends were tested using orthogonal polynomial contrasts. Secular changes in the association between physical activity and MetS were evaluated using random-effects meta-regression.RESULTS Physical activity levels showed no significant temporal trends from 2018 to 2023. Among MetS components, waist circumference and HDL-C showed significant linear and quadratic trends, fasting plasma glucose demonstrated a significant quadratic pattern peaking in 2021, and both triglycerides and diastolic blood pressure showed significant negative linear trends, whereas systolic blood pressure showed no significant temporal trend. Pooled analyses revealed that meeting physical activity guidelines was associated with a 25% lower odds of MetS (pooled OR = 0.75, 95% CI = 0.70–0.80). Meta-regression indicated no significant secular change in this association across survey years.CONCLUSIONS Meeting physical activity guidelines was consistently associated with lower odds of MetS among Korean adults from 2018 to 2023, with no evidence of secular change in this association. Despite stable physical activity, several MetS components showed partially unfavorable temporal trends, underscoring the need for prevention strategies beyond physical activity alone.

Background/Objectives: This study applies an Extended Theory of Planned Behavior, integrating parenting stress to examine factors influencing parental intentions to participate in health promotion programs for children with disabilities. Methods: Data (n = 345) were collected and analyzed using Structural Equation Modeling. Results: Results indicated that parenting stress affects intention indirectly through subjective norms and perceived behavioral control, with attitude playing a limited mediating role. Significant indirect effects were found from the child domain via attitude, and from the parent domain via both subjective norms and perceived behavioral control, while the sequential double-mediation pathway was not significant. Conclusions: These findings highlight the importance of addressing both social expectations and perceived capability in program design, alongside strategies to reduce structural barriers and enhance psychological and social support. Implications for culturally responsive interventions and the integration of action planning are presented.

OBJECTIVES The purpose of this study is to examine time trends in Health-Related Quality of Life (HQoL) among U.S. adults and to analyze the time-varying associations between Leisure-Time Physical Activity (LTPA) and HQoL.METHODS This study utilized data from the Behavioral Risk Factor Surveillance System (BRFSS) collected between 2018 and 2023. For the trend analysis of HQoL, a weighted intercept-only linear Time-Varying Effect Model (TVEM) was employed. To examine the temporal association between LTPA and HQoL, a weighted logistic TVEM was applied. Furthermore, a weighted logistic TVEM was used to assess the moderating effect of sex (male vs. female) on the relationship between LTPA and HQoL.RESULTS A total of 1,883,016 U.S. adults were included in the analysis. The mean number of unhealthy days increased from 2018 to 2019, reaching 8.83 days, then declined to 7.45 days in 2020. By late 2023, the mean number of unhealthy days reached its highest level over the study period at 9.06 days. From 2018 to 2023, the association between LTPA and HQoL remained stable over time. After adjusting for time-invariant covariates, a significant association between engaging in LTPA and better HQoL was confirmed. Additionally, sex-stratified analysis revealed that both men and women exhibited the strongest association in 2018. However, no statistically significant sex-based moderation effect was observed.CONCLUSIONS The findings of this study confirmed that the mean number of unhealthy days among U.S. adults showed a fluctuating pattern from 2018 to 2023, with the highest levels observed in late 2023. Throughout the study period, LTPA was consistently associated with higher odds of reporting better HQoL, and this association remained stable across time with no evidence of sex-stratified moderation. These findings highlight the potential public health relevance of maintaining regular LTPA to support perceived well-being during periods of societal disruption.

OBJECTIVES This study aims to examine the relationship between subjective body shape perception, physical activity, and sedentary behavior among South Korean adolescents.METHODS Data were obtained from the 2018–2023 Korea Youth Risk Behavior Survey (KYRBS), a nationally representative survey of South Korean adolescents. Subjective body shape perception was categorized into three groups: underweight, normal weight, and overweight. Physical activity was assessed based on self-reported frequency of moderate-to-vigorous exercise, while sedentary behavior was measured by daily sitting time.RESULTS A total of 307,926 adolescents (157,751 boys) were included in the analysis. Adolescents who perceived themselves as thin or normal were more likely to engage in physical activity compared to those who perceived themselves as overweight (OR=1.46 and OR=1.76, respectively; p<0.05). Boys with a normal body shape perception had a lower likelihood of engaging in sedentary behavior compared to those who perceived themselves as overweight (OR=0.93; p<0.05). However, no statistically significant association was observed between subjective body shape perception and sedentary behavior among girls.CONCLUSIONS The findings highlight the role of body shape perception in shaping physical activity levels among adolescents. Those who perceive themselves as overweight tend to engage in less physical activity, underscoring the need for interventions promoting accurate body shape perception and encouraging active lifestyles. Additionally, the absence of a significant association between body shape perception and sedentary behavior suggests the need for further research, particularly on culturally relevant sedentary behavior guidelines in South Korea.

VPURPOSE: Cardiorespiratory fitness is closely related to cardiovascular and chronic diseases and is an important predictor of mortality. Despite the significance of cardiorespiratory fitness, currently, a lack of research exists that validates the effectiveness of the 6-minute walk test, specifically in the Korean population. Therefore, the purpose of this study was to verify the validity of the 6-minute walk test for Korean older individuals and to develop a maximum oxygen consumption (VO2max) prediction equation.METHODS: A total of 167 participants were included in the final analysis, after excluding 33 of the 200 participants. Moreover, VO2max was measured by performing a submaximal exercise test on a treadmill, and the total distance and heart rate were measured using a 6-minute walk test. Pearson’s correlation coefficient was calculated to verify the criterion validity between VO2max and total distance in the 6-minute walk test. To develop a VO2max prediction equation, multiple regression analysis was conducted and cross-validation of the developed prediction equation was confirmed.RESULTS: The correlation coefficient between VO2max and the 6-minute walk test was 0.575 (p<.001). The adjusted R2 of the VO2max prediction equation using the 6-minute walk test was 0.449 (p<.001). The difference between the predicted VO2max and measured VO2max was 1.184±1.331 mL/kg/min, and the correlation coefficient was 0.594 (p<.001).CONCLUSION: The developed prediction equation consisted of explanatory variables that can be measured easily and were practical in the field. As entry into a post-aged society is imminent, managing older adult’s physical fitness has become a significant issue. In the future, if the validity verification is performed with a large number of people, the prediction formula developed in this study will be useful.