The prevalence of older population is growing rapidly. According to the national statistics in Korea, the proportion of older population was 7.2% in 2000, and the number is projected to double (i.e., 14%) in the year of 2018. A decreasing muscular endurance level, which is an inevitable phenomenon for older adults, has become the one of the major public health problems, yet little is known about the threshold of the aging curve for muscular endurance. The purpose of this study is to estimate thresholds of aging curve on the muscular endurance in Korean. The sit-up data (i.e., means and standard deviations of each age from 7 to 65 years old) were collected from 54 published research articles and national statistics in Korea between 1988 and 2005. All collected data were equated into a common scale (i.e., sit-ups/min) in order to compare scores across different data sets. Based on the collected means and standard deviations, a total of 254,811 pseudo data (123,288 = male and 131,523 = female) were generated using Microsoft Excel. To locate the threshold from curvilinear aging curve, Dmax method was used. The Dmax was defined as the point on the regression curve that yields the maximal distance to the straight line formed by the two end points of the curve. Pearson correlation coefficients and rate of change indexes were presented. The Dmax results showed that aged 18 was the aging threshold for male and female. The Pearson correlation coefficients between the sit-up scores and age were .673 and -.707 from below and above the threshold (i.e., aged 18) for male and .542 and -745 for female respectively. The rate of change results showed that male's sit-up scores increased at the rate of 6.53% per year until aged 18 and decreased at the rate of -2.29% per year above the threshold. The rate of change pattern for female was similar to that of male. Female's sit-up scores increased at the rate of 5.95% per year and decreased at the rate of -4.06% per year. In summary, the muscular endurance level started to decrease at aged 18 for both male and female. This study results help better explain a muscular endurance status in relation to aging in Korean population.
This work was supported by Korea Research Foundation Grant (KRF-2004-041-G00104).