In the present study, we evaluated the prevalence of LS and sarcopenia. Furthermore, we assessed the knee extension strength, balancing ability, and sarcopenia in relation to LS. The total number of participants was 312 (75.5%) for those diagnosed as LS and 49 for those diagnosed as sarcopenia (11.8%). Knee extension strength and one-leg standing test between the no LS and LS groups, knee extension strength was significantly lower in the LS group. Particularly in males, sarcopenia patients could be assumed to have LS, but non-sarcopenia patients may or may not have LS.
A characteristic feature of this study was the collection of participants with age ranging from 50 to 89 years by randomly sampling from the resident register. Compared to conventional research on residents that recruits active volunteers, this research was designed to create a cohort that more accurately reflects common residents. In addition, another unique feature of this study was that we gathered approximately 50 participants for physical examinations in each age group and sex, and as a result, the age and male-female ratio of participants aged 50-89 years were uniformly distributed. This uniform distribution is advantageous for performing accurate statistical comparisons between sexes or age groups.
The prevalence of LS in this study increased with age, with approximately half of the participants aged 50-59 years and over 90% aged 70-79 years and 80-89 years who were diagnosed as LS. In previous studies [4-7] and in this study, there are differences in the composition ratio for age and sampling method of subjects; thus, cannot simply compare the rate of prevalence for LS in this study with results from previous studies. However, the prevalence of LS in this study was comparable to the prevalence of LS described in a study by Yoshimura et al. [4] that calculated the rate of prevalence by age and sex. On the other hand, when comparing the ratio of participants who were diagnosed with LS by each criterion in the LS risk test, the ratio in this study was greater than in the study by Yoshimura et al in terms of those with difficulties in maintaining a one-leg stand from a 40-cm-high seat during the stand-up test. In contrast, the ratio of participants who obtained a two-step test score >1.3 was less than what was reported by Yoshimura et al. There was no significant difference between both studies in terms of the results in 25-question GLFS. The reason for the difference in results for each criterion in diagnosing LS is unknown. However, there are reports that suggest that the average step count increases with size of the city [18] and that those who exercise at a moderate or higher intensity are greater in urban areas than in rural areas [19]. We suspect that the results of the stand-up test in this study were inferior to other studies due to decrease in the muscle strength of knee extension as a result of the comparatively small amount of daily physical activity in residents of rural areas.
When comparing the physical function between the no LS and LS groups, the knee extension strength was significantly lower in both male and female participants with LS aged 50-59 years, and female participants aged 60-69 years. From this fact, we believe that some measures to prevent or improve LS may require exercise to increase the muscle strength of the lower limbs.
In terms of the prevalence of sarcopenia in the general elderly population of Japan, one report described that the SP prevalence according to age group stratifications of 60-64, 65-69, 70-74, 75-79, and ≥80 years were 0.5, 0.0, 4.3, 11.2, and 27.0%, respectively [20]. The prevalence of sarcopenia was higher when comparing each age group with past reports. In the present study, the total prevalence of sarcopenia was 11.8%, which was slightly higher than in previous studies.
While there have been reports that describe no gender difference in the prevalence of locomotive syndrome and sarcopenia [5,20,21], there have also been reports that describe a higher prevalence of sarcopenia in males compared to females [22]. Significant associations between sarcopenia and locomotive syndrome were found in both genders based on the results of the ROAD study, which is a study of Japanese residents aged 60 and over [12]. On the other hand, the results of this study showed that males had a significant association between sarcopenia and locomotive syndrome, while females exhibited a comparatively lower positive likelihood ratio. There are several possibilities as to why this difference may have occurred. First, the sample size may have been insufficient. The results for females could be clarified with a larger sample population. However, other causes should also be considered. The cause of locomotive syndrome, which is more common in females, might have been implicated. For example, osteoporosis and knee osteoarthritis are common in females [5]. Moreover, gender differences in diagnostic criteria for sarcopenia might have been affected.
There are several limitations in this study. First, although the research design reduces the sampling bias by adopting random sampling from the resident register, we may not have been able to control for all potential biases as a result of the low participation rate. Secondly, the standard of sarcopenia in this study was defined by grip strength and SMI, and walking ability was not considered. Therefore, prevalence may differ if the standard was interpreted more stringently. Finally, we cannot deny the possibility that regional characteristics of rural areas were reflected in the results of this study.
In conclusion, a characteristic feature of this study was the collection of participants with age ranging from 50 to 89 years by randomly sampling from the resident register. Therefore, this research was designed to create a cohort that more accurately reflects common residents. The prevalence of LS in this study increased with age, with approximately half of the participants aged 50-59 years and over 90% aged 70-79 years and 80-89 years who were diagnosed as LS. Due to difficulties in maintaining the one-leg stand from a 40-cm-high seat during the stand-up test, many participants were diagnosed as LS. Moreover, the knee extension strength was significantly lower in both male and female participants with LS aged 50-59 years, and female participants aged 60-69 years. From this fact, we believe that some measures to prevent or improve LS may require exercise to increase the muscle strength of the lower limbs.