This study showed a significant decrease in WtHR and increase in total cholesterol from year 2014 to 2017. The other variables such as SBP, DBP, AST, ALT, TG, BMI did not show any trends from year 2014 to 2017. However, this study showed a significant decrease in HG and HGtW ratio among adolescent participants over the years from 2014 to 2017. The results of this study indicate more than just muscle strength is decreasing in adolescents over the years. Some studies have demonstrated a relationship between muscle mass and current health status.[1, 14] Cohen et al. showed the importance of muscle strength being associated with metabolic risk factors in children.[20] Moreover, Grontved et al. showed that adolescents’ muscle strength is associated with cardiovascular risk in young adulthood.[21] Some studies argue that muscle mass alone cannot explain the patients’ overall health status.[22] Therefore, Meng Ge et al. suggested that assessing muscle strength may be more valuable than measuring muscle mass.[14] Thus, HGtW represents muscle quality and is more important than HG alone. However, HGtW is decreasing in adolescents in Korea along with a decrease in HG. This indicates that Korean adolescents’ muscle strength and quality are both decreasing over the years. In addition to the above-mentioned metabolic syndrome-related diseases, many studies have demonstrated HG’s relationship with functional and psychological health as well as quality of life.[11, 12, 16, 23] The decrease in HG and HGtW indicates that there is overall health problem in Korean adolescents, more than just decrease in the force of simple muscle strength.
A recent study of handgrip cutoffs performed in children and adolescents in Colombia reported that the lower the HGtW ratio, the higher the likelihood of cardiometabolic risk.[24] Compared with the HG cut-off presented in a previous study, the HGtW ratio among boys and girls aged 10–12 years are higher (0.376 for boys and 0.359 for girls). In the present study, from 2014 to 2017, boys over 13 years of age showed an HGtW higher than the cut-off value (0.447 for boys) in a previous study. Girls’ HGtW, however, was higher than the cut-off value (0.440 for girls) in year 2014, but the HGtW was found to be low in 2017. HGtW of Korean adolescents are higher than the cut-off value seen in the Colombia study, but it is declining over the years. Specifically, in 2017, HGtW of girls over 13 years of age were lower than the cut-off value. Further evaluation and management of Korean adolescents’ overall health is necessary.
Other variables except WtHR and cholesterol does not show significant trends over years, but HG and HGrW are decreasing over years and it can be affected by various variables as mentioned above. We cannot be satisfied for Korean adolescents are safe even the variables such as SBP, DBP, AST, ALT, TG, BMI did not change over years. The socioeconomic status, dietary intake, physical activity, and mental status, many other variables can be affected health of Korean adolescents. Currently, the situation in Korea does not seem to be irrelevant. The health status can be easily inferred by HG and HGtW, and this study implies the risk of health problems of Korean adolescents have begun to develop.
This study has a few limitations. First, in the KNHANES, muscle mass was not measured using dual-energy X-ray absorptiometry or imaging studies, such as computed tomography. These data should be added for adolescents in the KNHANES in the future. Second, there is a lack of information on the cut-off value of HGtW in Korean adolescents. If additional data are collected or cohorts are built in the future, it may be possible to determine cut-off values. Third, missing data were present that could affect the result. Further effort is needed to minimize the missing data because it represents the whole Korean adolescent. Fourth, puberty can affect the result of handgrip strength, however, tanner staging data is missing in KNHANES data. Fifth, physical activity, dietary intake or socioeconomic status can affect handgrip strength, but these variables were excluded in analysis.[27] Further study is needed to evaluate cause of decrease in HG and HGtW in Korean adolescents. However, despite these limitations, this is the first large-scale study to evaluate trends of handgrip strength in Korean adolescents.
In conclusion, the results of the present study showed a decrease in HGtW in Korean adolescents, which might be indicative of a problem in overall health status among Korean adolescents. Decrease in HGtW might be caused by such as increase in metabolic risk or mental health problem, decrease in physical activity or having dietary intake problem. To our knowledge, this is first study to evaluate trends of HG and HGtW in adolescents and to show changes over the years. HGtW is a measure of muscle quality; the overall decrease suggests deterioration of the quality of muscles among Korean adolescents. Hence, there is a need to review the health of Korean adolescents, and measures should be taken to prevent its deterioration.