We performed a cross-sectional analysis between May 2015 and November 2016. In total, 143 healthy community-dwelling individuals (ages: 40-85 years) were included in this study. Of the 143 subjects, 63 were excluded because they had a history of regular sports (tennis and cycling), resistance training (body weight, tube and/or machine), participation in exercise intervention experiments, or were under 60 or over 80 years old. A total of 80 healthy, community-dwelling older adults (40 men and 40 women; age: 60-79 years) were included in the present study. The participants had not history of resistance training, cycling, and other sports activity (i.e., tennis, golf, cycling etc.) for at least 1 year prior to the start of the study. We excluded individuals who were unable to follow our instructions and those with chronic orthopedic conditions or any health or medical condition that limited the ability to undertake light-to-moderate walking. In addition, the participants completed a self-report questionnaire regarding medical history and comorbid conditions. All participants were informed of the study methods, procedures, and risks, and each signed an informed consent document before participating in the study. This study was approved by the Ethics Committee of the Juntendo University (Approval Number: 26–75).
To screen the presence of LS, the participants were tasked to perform the two-step test and stand-up test as functional tests , and were asked to answer the GLFS-25 questionnaire . The participants stood with the toes of both feet behind a starting line. They were instructed to take two long steps (as long as possible) and to align both feet. The length of the two steps from the starting line to the tips of the toes was measured. The two-step test score was calculated using the following formula: length of the two steps (cm) / height (cm). The participants were also instructed to stand using one or both legs from a specific height. Seats were placed at the following heights: 40, 30, 20, and 10 cm. The participants stood up from each seat (in descending height order) using both legs, and then using each leg separately. A participant passed the test at the specified height if they were able to stand up without leaning back to gain momentum and maintain the posture for 3 sec. The GLFS-25 is a self-administered, comprehensive questionnaire consisting of 25 items, that assessed the patient’s pain (4), ADL (16), social function (3), and mental health status (2) during the last month. These items are graded using a five-point scale from 0 (no impairment) to 4 points (severe impairment). The scores are added to produce a total score (minimum = 0, maximum = 100). A higher score is associated with worse locomotive function. Our previous study  indicated that the measured variables from the stand-up test, two-step test, and GLFS-25 have enough validity and reliability, with the intra-class correlation coefficients being 0.87, 0.93, and 0.76 and Cronbach’s α being 0.93, 0.95, and 0.88, respectively. These tests were used to assess declines in mobility of each participant.
The JOA has proposed clinical decision limits for these tests in the assessment of LS . According to the results of the LS test, the participants were classified as having LS when a participant met one or more of the following criteria: (1) two-step test score < 1.3, (2) difficulty in standing from a seat at a height of 40 cm using one leg in the stand-up test (either leg), and (3) GLFS score ≥ 7 . All other participants were placed in the non-LS group. In this study, we focused on the stage 1 of JOA definition of LS considered as LS group (including stage 1 and 2; n=35 and 6), and the independent values were compared between the LS and non-LS groups.
Habitual daily PA
We measured daily PA using a three-axis accelerometer (UW-301, A&D, Toshima, Tokyo). The participants were instructed to wear the accelerometer around the wrist continuously for 9–14 days except during dressing and bathing. Accelerometer readings recorded for a minimum of 7 continuous days, excluding the distribution and collection days, were considered in the study; days wherein the accelerometer was not worn for more than 2 hours were excluded . Activities were classified into five levels of intensity, according to the accelerometer data: 1, resting (< 1.1 METs); 2, sitting behavior (1.1–1.4 METs); 3, standing behavior (1.5–2.9 METs); 4, moderate PA (3.0–5.9 METs); and 5, vigorous PA (≧ 6 METs). The sum of the time spent in moderate and vigorous PA (≧ 3 METs) was calculated and defined as MVPA. Additionally, the sum of the time spent in resting and sitting behaviors (< 1.5 METs) was calculated and defined as RSB.
Anthropometrics and body composition
Anthropometric measurements included height (cm), weight (kg), and body mass index (BMI, weight [kg] / height [m2]). Body composition measurements included body fat, muscle mass, and waist-to-hip ratio; these were estimated by bioelectrical impedance analysis (BIA) using a body composition analyzer (InBody 730, Biospace Co. Ltd, Seoul, Korea). Appendicular skeletal lean mass (ALM) was calculated as the sum of the muscle mass of the arms and legs . We calculated the skeletal muscle index (SMI) as follows: SMI = ALM/height2.
Maximal isometric strengths of leg muscle
The maximal voluntary isometric strength of the knee extensors was determined using a dynamometer (Takei, Tokyo, Japan). Each participant was seated on a chair with the hip joint angle at 90° flexion (0° = full hip extension). Prior to the test, several warm-up contractions (2–3 submaximal contractions and 1–2 near-maximal contractions) were performed. They were instructed to perform maximum isometric knee extensions two or three times. The best recorded value was used as the representative, and the weight bearing index (knee strength/ body weight; KE-WBI) was calculated. However, five participants were unable to perform the test due to high blood pressure which was measured before conducting the test. With regard to knee extension strength, the test-retest (inter-session) reliabilities using ICC, SEM, and minimal difference were 0.945, 3.41 kg, and 9.45 kg, respectively.
Data are presented as means ± standard deviations (SD). Differences between the non-LS and LS groups were determined using the unpaired Student’s t-test. Relationships among the three LS parameters, daily PA, and anthropometric and body composition measurements were examined using Pearson’s product-moment correlation analysis. Finally, this study conducted binomial logistic regression analyses (LRA) to examine the statistical relationships between daily PA and category of LS adjusting for sex difference and age. For this analysis, the continuous variables of daily PA were divided into quartile categories (Table 4). All analyses were performed using SPSS software (ver. 24; SPSS Inc., USA). Statistical significance was set at p < 0.05.