Lower extremity muscle strength is a factor in the early stage of development of locomotive syndrome in Japanese American women: A cross-sectional study

doi:10.21203/rs.3.rs-1705881/v1

Background

Obesity and lower extremity muscle strength (LEMS) is a factor in the development of locomotive syndrome (LS), but the influence of gender differences on its development has not been clarified. We aimed to determine whether obesity and LEMS are associated with LS by sex, using a Japanese American population with a high prevalence of obesity.

Methods

The study was a cross-sectional study of 564 people living in Los Angeles, United States of America. The LS stage was graded using the 25-question Geriatric Locomotive Function Scale. The LEMS was determined by the knee extension force (KEF). Logistic regression analysis was performed to investigate the relationships between LS stage and KEF, age, and obesity-related parameters.

Results

No significant differences were found in the prevalence rates of non-LS, stage 1 LS, and stage 2 LS among the different age groups for men. In contrast, significant differences were observed in the LS prevalence rates the different age groups for women. In men, KEF was significantly lower in the stage 2 LS group than in the non-LS group. Conversely, in women, KEF was significantly lower in the stage 1 LS and stage 2 LS groups than the non-LS group. KEF was significantly associated with LS in the stage 2 LS group in men, while age and KEF were significantly associated with LS in the stage 1 LS and stage 2 LS groups in women.

Conclusions

KEF was found to be a factor in the development of stage 2 LS in men and stages 1 and 2 LS in women. Therefore, efforts to prevent muscle weakness in KEF from the early stage of LS in women are considered a necessary intervention.

Locomotive syndrome

lower extremity muscle strength

obesity

In Japan, the increasing number of elderly people is becoming a social problem, and according to the Annual Report on the Ageing Society FY2021, by 2036, 33.3% of the population will be aged 65 years or over [1]. A particular problem resulting from this ageing population is the increase in the number of people requiring nursing care. Therefore, there is an urgent need to extend healthy life expectancy in Japan, so that less nursing care will be required. One factor contributing to the need for nursing care is the impairment of the locomotor system. In 2007, the Japanese Orthopaedic Association (JOA) proposed the concept of locomotive syndrome (LS) [2]. This is a condition in which mobility is impaired due to musculoskeletal disorders. Deterioration of the locomotive organs, such as bones, joints, and muscles, results in impaired activities of daily living (ADLs), such as walking, standing up, and sitting down. If it progresses, LS increases the risk of long-term care requirements and can ultimately result in patients becoming bedridden [3].

Obesity has been shown to contribute to loss of mobility. A study of 165 Japanese women with an average age of 68 years reported that women with LS had a significantly larger body mass index (BMI) than those without LS. Multivariable analysis identified BMI as a significant predictor of LS, and indicated that a BMI of 23.5 kg/m² is the cut-off value for predicting LS [4]. Another study found that an increase in weight contributed to LS, independent of age, due to the increased burden on the lower leg joints [5]. A study of 217 Japanese women with an average age of 68 years analysed obesity-related parameters and found that waist circumference (WC) was strongly associated with LS [6].

Muscle strength is another important factor influencing motor function. Studies on Japanese subjects have reported that back muscle strength [7] and handgrip strength [8] are associated with LS. In addition, the two-step test, a dynamic assessment of LS, and the stand-up test can be used to measure lower extremity muscle strength (LEMS). In particular, the two-step test was developed to assess walking ability, including LEMS, and is widely used in clinical practice [9]. Among LEMS, knee extension force (KEF) can be easily assessed clinically with a hand-held dynamometer. KEF is presumed to be related to the onset of LS, as it plays an important role in ADL [10, 11]. While KEF muscle weakness is associated with severity of knee osteoarthritis [12], the relationship between KEF and LS is not clear.

However, obesity and LEMS, are both strongly influenced by sex differences and can influence the development of LS. The 2018 National Health Survey revealed that the proportion of obese people (BMI ≥ 25 kg/m²) was 32.2% for men and 21.9% for women in Japan [13], indicating a lower frequency of obesity in women compared to men. Similar results were reported by our study on Japanese Americans [14]. A study including subjects aged 45–78 years reported that KEF was higher in men than in women, but that it decreased with age [15]. A community-based survey investigating sex differences in LS using the Geriatric Locomotor Function Scale (GLFS-25) reported a mean score of 6.7 for men and 9.2 for women [16]. Thus, in Japan, LS is more likely to occur in women than in men. However, the factors contributing to the different development of LS between the sexes has not yet been clarified.

The Hawaii-Los Angeles-Hiroshima Study investigated differences in disease structures due to Westernisation of lifestyle between a cohort of native Japanese people living in Japan and Japanese Americans living in the USA. It was found that Japanese Americans had a higher obesity prevalence than native Japanese people in Japan [14, 17–19]. Therefore, the purpose of this study was to determine whether obesity and LEMS are associated with the incidence of LS in different sexes, using a Japanese American population with a high proportion of obese individuals.

2.1 Participants and ethical considerations

In July 2015, 590 Japanese Americans aged between 18 and 96 years underwent health check-ups in Los Angeles, California. Additional mobility assessments were performed for this study. Of these, 564 participants were included in the analysis. Twenty-six individuals who were unable to walk independently, had a history of cerebrovascular disease, had undergone orthopaedic surgery, or were currently being treated for musculoskeletal conditions were excluded.

After receiving an explanation of the study procedures, each participant provided written informed consent. This study was approved by the Hiroshima University Ethics Committee (approval No. E-139) in accordance with the provisions of the Declaration of Helsinki.

2.2 Screening for locomotive syndrome

As candidate indices, the JOA proposed the following three tests to assess the risk of LS: the 2-step test, stand-up test, and GLFS-25. In the present study, the GLFS-25 was used for the detection of LS. This consists of 25 items with a score of 0–4 for each item [20]. The total score (ranging from 0 to 100) was used for the analysis, with a higher score indicating a worse condition. The JOA determined the clinical decision limits of the GLFS-25 to assess the risk of LS [21]. A GLFS-25 score of ≥ 7 was defined as stage 1, LS or an initial decline in mobility. Furthermore, a GLFS-25 score of ≥ 16 was defined as stage 2, LS and was associated with a progressive decline in mobility [2].

2.3 Assessment of muscle strength

The LEMS employed the maximum isometric KEF and was measured by a hand-held dynamometer (HHD; µTas F-1, Anima Inc., Tokyo, Japan) with a fixed belt. The correlation coefficient between the isometric KEF measured with an HHD and a stabilization belt versus that measured with an isokinetic dynamometer was 0.75, which makes it possible to achieve levels of reliability equivalent to measuring the muscle force [22]. The absolute value for isometric KEF (kgf) based on body weight (kg) was used to calculate the relative value for %KEF (%).

2.4 Assessment of obesity-related parameters

For obesity-related parameters, in addition to BMI, WC (the area at the umbilicus) was used [23].

2.5 Statistical analyses

The GLFS-25 scores and other participant characteristics were compared by sex and age (age groups: < 40, 40–49, 50–59, 60–69, 70–79, and ≥ 80 years). The GLFS-25 scores for men and women were compared according to the indication of stage 1 LS or stage 2 LS. Chi-squared and Z-tests were used for categorical variables, and one-way analysis of variance (ANOVA) was used for continuous variables. One-way ANOVA and Tukey’s honestly significant difference test were used to compare the characteristics of non-LS, stage 1 LS, and stage 2 LS for each sex. Logistic regression models with GLFS-25 scores indicating stage 1 LS (1: <7, 2: ≥7) or stage 2 LS (1: <7, 2: ≥16) with sex as a response variable were used to examine whether %KEF, age and obesity-related parameters were explanatory variables. P-values < 0.05 were considered statistically significant. IBM®SPSS® software, version 24 (IBM Corporation, Armonk, NY, USA) was used for all statistical analyses.

The average age of the men included in the analysis in this study was 60.1 ± 14.6 years, whereas the average age of the women was 62.4 ± 12.7 years. The mean BMI of the participants was 24.6 ± 3.5 kg/m² for men and 22.3 ± 3.3 kg/m² for women.

Table 1 shows the comparisons of LS stage and characteristics by age group for each sex. The prevalence of stage 1 LS and stage 2 LS was found to increase with age in both men and women. No significant difference was found in the prevalence rates of non-LS, stage 1 LS, and stage 2 LS in each age group for men. In contrast, a significant difference was found in the prevalence rates of non-LS, stage 1 LS, and stage 2 LS in each age group for women (P < 0.001). For KEF and %KEF, significant between-group differences were noted in both sexes, indicating that muscle strength declined with age (KEF and %KEF: P < 0.001). In men, BMI and WC did not differ significantly between ages, but in women, BMI and WC increased with age (BMI, P = 0.008; WC, P < 0.001).

Table 2 compares the characteristics of men and women who were classified into the non-LS, stage 1 LS, and stage 2 LS groups. The mean age for men was significantly higher in the stage 2 LS group than that in the non-LS group (P = 0.008). Among women, the stage 1 LS and stage 2 LS groups has a significantly higher mean age compared to the non-LS group (P < 0.001). In men, KEF and %KEF values were significantly lower in the stage 2 LS group than in the non-LS group (P < 0.001). On the other hand, in women, KEF and %KEF values were significantly lower in the stage 1 LS and stage 2 LS groups than in the non-LS group (P < 0.001, respectively). In addition, the BMI of women was significantly greater in the stage 2 LS group than in the non-LS group (P = 0.029). WC was not significantly different between the groups in men, but tended to be significantly higher in women in the 1 LS and 2 LS groups compared to the non-LS group (P = 0.065).

Table 3 shows the results of a logistic regression analysis of factors related to LS with %KEF, age, BMI, and WC as explanatory variables. The results showed that those variables were not significantly different in the stage 1 LS groups in men (Model 1), but %KEF was a factor in the stage 2 LS groups (model 2). The odds ratios (ORs) of the response variable was 0.916 for %KEF in the stage 2 LS groups. In women, %KEF and age were factors in the stage 1 and stage 2 LS groups (Model 3 and Model 4). The response variable for OR in women in the stage 1 LS groups 0.966 for %KEF and 1.056 for age. In the stage 2 LS groups was 0.940 in %KEF and 1.069 in age.

In this study, the prevalence of stage 1 LS and stage 2 LS was found to increase with age in both men and women, and the average prevalence rates were 19% and 7%, respectively, in men, and 24% and 11%, respectively, in women. The "Research on Osteoarthritis and Osteoporosis" (ROAD) study evaluated the prevalence of LS in men and women using the GLFS-25 in a Japanese population. The results showed that the prevalence of stage 1 LS and stage 2 LS was 18.8% and 9.0% in men, and 24.5% and 11.4% in women, respectively [21]. Furthermore, the mean prevalence of LS increased with age, and the prevalence of stage 1 LS and stage 2 LS in both sexes was similar to that observed in this study.

In previous Japanese studies, BMI and WC have been associated with stage 2 LS in elderly women [4, 6]. In the present study, BMI was higher in the stage 2 LS group than the non-LS group, and WC in women tended to be higher in the stage 1 LS and stage 2 LS groups compared with the non-LS group. However, multivariate analysis revealed that BMI and WC were not associated with LS in women. In Japanese elderly women, being overweight is a risk factor for LS because mechanical overload on weight-bearing joints can accelerate the degeneration of cartilage, and increase static compressive loading and pressures associated with postures that may damage disc integrity [24]. Nevertheless, it is necessary to identify lifestyle-related factors other than obesity that influence the development of LS in Japanese American women.

In this study, KEF was significantly associated with stage 2 LS in men, with no association by age. In contrast, both age and KEF were associated with stage 1 LS and stage 2 LS in women, suggesting that factors contributing to LS differ according to sex. To the best of our knowledge, this is the first study to report an association between KEF and LS, and suggests that KEF is more relevant for stage 2 LS, where mobility is already reduced in both men and women. With regard to age, in a study conducted in Japan, an association was found between GLFS-25 and age in women, but not in men. Furthermore, the percentage of stage 1 LS and stage 2 LS increased with age in Japanese women [25], suggesting that age is a factor for LS, not only in Japanese women, but also in Japanese-American women.

However, the involvement of KEF in LS in women has not been clarified, and in particular, there are few reports on stage 1 LS in women. Sedentariness was reported to be significantly associated with education, female sex, age, and place of birth outside the USA, among other factors, according to the County Health Survey of 8,353 Los Angeles adult residents. In addition, 41% of Los Angeles residents have been reported to have a sedentary lifestyle, with women being almost twice as likely to be sedentary as men [26]. Furthermore, physical inactivity is known to be associated with reduced lower limb muscle mass [27]. Therefore, although actual sitting time was not measured in this study, it is possible that KEF may be involved in stage 1 LS, as the women in this study spent more time sitting than the men.

There are several limitations to the present study. First, the participants were only from Los Angeles; thus, they may not represent all Japanese Americans. Additionally, considering that Los Angeles has 36,992 Japanese American residents [28], the number of participants included in this study was relatively low. Next, LEMS was limited to KEF; therefore, it is unclear if KEF is the best LEMS parameter for predicting the prevalence of LS as KEF.

This is the first study to demonstrate the association between LEMS and LS. KEF was found to be a factor in the development of stage 2 LS in men, and stages 1 LS and 2 LS in women. Therefore, efforts to prevent muscle weakness in KEF from the early stage of LS in women are considered a necessary intervention.

LS - locomotive syndrome

LEMS - lower extremity muscle strength

KEF - knee extension force

JOA - Japanese Orthopaedic Association

ADL - activities of daily living

BMI - body mass index

WC - waist circumference

GLFS-25 - Geriatric Locomotor Function Scale

HHD - hand-held dynamometer

ANOVA - one-way analysis of variance

OR - odds ratio

ROAD - Research on Osteoarthritis and Osteoporosis

Ethics approval and consent to participate

This study was approved by the Hiroshima University Ethics Committee (approval No. E-139) in accordance with the provisions of the Declaration of Helsinki. All participants provided written informed consent.

Consent for publication

Not applicable

Availability of data and materials

The datasets used and analyzed during the current study available from the corresponding author on reasonable request.

Competing interests

The authors declare that they have no competing interests

Funding

This work isn't receiving any funding.

Authors' contributions

MY and HO conceived the concept and design of the study. TK, HO and MY obtained the patient data. YN and TN analyzed and interpreted the data. TK, MY, HO, TN and YN prepared the manuscript. All authors read and approved the final manuscript.

Acknowledgements

This survey was supported by the members of the Hiroshima Kenjin-Kai Associations of Los Angeles, California.

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Table 1 Prevalence of locomotive syndrome and characteristics of participants by sex and age.

Parameters	All	<40 years	40-49 years	50–59 years	60–69 years	70–79 years	≥80 years	P-value
Men
N	216	20	34	36	67	47	12
Non-LS	161 (74)	18 (90)	28 (82)	26 (72)	51 (76)	33(70)	5(42)	0.108
Stage 1 LS	40 (19)	2 (10)	4 (12)	9 (25)	12 (18)	9 (19)	4 (33)
Stage 2 LS	15 (7)	0 (0)	2 (6)	1 (3)	4 (6)	5 (11)	3 (25)
KEF (kgf)	34±8	36±9	38±7	39±9	33±7	28±6	24±7	<0.001
%KEF (%)	49±11	54±13	53±11	55±11	48±9	42±8	38±11	<0.001
BMI (kg/m²)	24±3	23±3	24±4	24±3	24±3	25±3	24±2	0.405
WC (cm)	88±8	83±8	88±10	88±8	89±8	90±7	88±4	0.053
Women
N	348	21	35	66	116	91	19
Non-LS	226 (65)	18 (86)	30 (85)	54 (81)	80 (69)	39 (43)	5 (26)	<0.001
Stage 1 LS	82 (24)	2 (10)	3 (9)	9 (13)	29 (25)	33 (36)	6 (32)
Stage 2 LS	40 (11)	1 (4)	2 (6)	3 (6)	7 (6)	19 (21)	8 (42)
KEF (kgf)	23±6	25±5	27±6	26±5	22±5	21±5	15±5	<0.001
%KEF (%)	43±11	47±9	50±10	48±10	42±10	39±9	30±8	<0.001
BMI (kg/m²)	22±3	20±1	21±3	21±3	22±3	23±3	22±3	0.008
WC (cm)	81±10	73±6	77±9	78±9	83±10	84±10	83±7	<0.001

Values are presented as number (%) or mean± standard deviation., LS, locomotive syndrome; KEF, knee extension force; %KEF, KEF/body weight×100; BMI, body mass index; WC, waist circumference. P-values were derived from the chi-square test or one-way analysis of variance.

Table 2 Comparison of the characteristics of the participants with and without locomotive syndrome stage.

Parameters	Men				Women
Parameters	Non-LS (n=161)	Stage 1 LS (n=40)	Stage 2 LS (n=15)	P-value	Non-LS (n=226)	Stage 1 LS (n=82)	Stage 2 LS (n=40)	P-value
Age (years)	58.5±14.9^a	62.8±11.9^ab	69.6±13.2^b	0.008	59.1±12.4^a	67.3±10.1^b	70.5±12.5^b	<0.001
KEF (kgf)	35.2±8.8^a	31.8±8.5^ab	27.1±7.7^b	<0.001	24.5±5.6^a	21.6±5.9^b	19.6±5.6^b	<0.001
%KEF (%)	50.8±11.7^a	46.8±11.1^ab	40.3±9.1^b	<0.001	45.8±10.3^a	39.6±11.4^b	36.0±10.6^b	<0.001
BMI (kg/m²)	24.7±3.6	24.4±2.6	24.9±3.6	0.684	22.1±3.2^a	23.0±3.8^ab	23.6±3.8^b	0.010
WC (cm)	88.9±9.0	88.8±6.7	90.0±9.6	0.892	80.4±9.7	83.3±10.9	84.2±9.8	0.065

Values are presented mean± standard deviation. LS, locomotive syndrome; KEF, knee extension force; %KEF, KEF/body weight×100; BMI, body mass index; WC, waist circumference.

P-values were derived from a one-way analysis of variance. The results of Tukey’s honestly significant difference test are shown by the superscripted letters a and b, with the same letters representing no significant difference and different letters representing significant differences.

Table 3 Logistic regression analysis by sex with stage of locomotive syndrome as response variable.

Men
Response variable: non-LS or stage 1 LS					Response variable: non-LS or stage 2 LS
Explanatory variable		OR	95% CI	P-value	Explanatory variable		OR	95% CI	P-value
Model 1	%KEF	0.975	0.940-1.011	0.170	Model 2	%KEF	0.916	0.857-0.980	0.007
	Age	1.013	0.985-1.041	0.370		Age	1.037	0.990-1.087	0.100
	BMI	0.898	0.726-1.110	0.317		BMI	1.120	0.803-1.564	0.503
	WC	1.017	0.931-1.111	0.707		WC	0.937	0.809-1.084	0.373
Women
Response variable: non-LS or stage 1 LS					Response variable: non-LS or stage 2 LS
Explanatory variable		OR	95% CI	P-value	Explanatory variable		OR	95% CI	P-value
Model 3	%KEF	0.966	0.938-0.995	0.020	Model 4	%KEF	0.940	0.896-0.987	0.010
	Age	1.056	1.026-1.086	<0.001		Age	1.069	1.025-1.115	0.001
	BMI	1.028	0.906-1.165	0.671		BMI	1.106	0.930-1.314	0.249
	WC	0.996	0.953-1.040	0.845		WC	0.962	0.901-1.026	0.229

LS, locomotive syndrome; OR, odds ratio; CI, confidence interval; %KEF, knee extension force/body weight × 100; BMI, body mass index; WC, waist circumference.

Response variables: 1 = non-LS, 2 = stage 1 or 2 LS. The explanatory variables, %KEF, age, BMI and WC　were the explanatory variables in all model.

No competing interests reported.

Lower extremity muscle strength is a factor in the early stage of development of locomotive syndrome in Japanese American women: A cross-sectional study

Status:

Version 1

Abstract

Background

Methods

Results

Conclusions

1. Introduction

2. Materials And Methods

2.1 Participants and ethical considerations

2.2 Screening for locomotive syndrome

2.3 Assessment of muscle strength

2.4 Assessment of obesity-related parameters

2.5 Statistical analyses

3. Results

4. Discussion

5. Conclusion

List Of Abbreviations

Declarations

References

Tables

Additional Declarations

Status:

Version 1