Comparison of lower leg muscle strength and grip strength for diagnosing slower gait speed in the elderly.

OBJECTIVES: Sarcopenia, decreased muscle volume and muscle weakness in the elderly is a serious risk of various adverse outcomes. Current diagnostic procedure for sarcopenia includes gait speed, grip strength, and percentage of skeletal muscle volume. However, lower leg muscle strength decreases much faster than grasp power, and we have evaluated the usefulness of its measurement using a recently developed instrument (Locomoscan).
METHODS: Forty-three institutionalized elderly subjects were evaluated for their anthropometrical parameters, body composition, grasp and lower leg muscle strength, and gait speed. They were categorized into 2 groups; gait speed equal to or higher than 0.8 m/s and that below 0.8 m/s.
RESULTS: Leg muscle strength per body weight was significantly greater in those with their gait speed equal to or higher than 0.8 m/s, whereas there was no significant difference in other parameters. Receiver operator characteristics analysis has shown that leg muscle alone significantly predicted the greater gait speed.
CONCLUSIONS: Lower leg muscle strength can be useful for predicting gait speed.

Introduction

Japan has become a rapidly aging society. The percentage of subjects aged 65 and over is now as high as 25.1% of the Japanese population in 2014 [1]. Life expectancy is 80.50 years for men, and 86.83 years for women [2]. However, healthy life expectancy is much shorter than these values; 70.42 years for men and 73.62 years for women [3], and the difference between life expectancy and healthy life expectancy is 10.08 years for men and 13.21 years for women. Elderly subjects are likely to spend these years in the diseased states and at higher risk of being in need of care, which is a great burden to the individual and also to the society. Number of persons requiring long-term care has increased by 1.23 times between 2000 and 2014 [4].

The leading underlying diseases in need for nursing care are cerebrovascular disease (18.5%), dementia (15.8%), and frailty (13.4%) as a whole. In contrast, musculoskeletal diseases constitute the major underlying causes for light care; joint disease (20.7%), frailty (15.4%), and falling and fracture (14.6%) [5]. Elderly subjects requiring light care is quite likely to have shortened healthy life expectancy, even though the biological life expectancy is not much affected. Thus, prevention of the musculoskeletal disorders is essential for the health promotion of the elderly.

Sarcopenia refers to a state with progressive and generalized loss of skeletal muscle mass and strength, resulting in a higher risk of various adverse outcomes such as physical disability, impaired quality of life and even higher mortality [6], [7]. A diagnostic guideline for sarcopenia was published by European Working Group on Sarcopenia in Older People (EWGSOP), which was adopted by Japan Geriatric Society. In brief, subjects are first screened into those with gait speed equal to or higher than 0.8 m/s and those below it. They are further categorized based on the grip strength and percentage of skeletal muscle volume [6].

Two issues were our concern regarding this diagnostic protocol. First one is the validity to evaluate sarcopenia by the muscle mass. Muscle mass can be measured by various methods such as computed tomography, magnetic resonance imaging, dual energy X-ray absorptiometry, and also by bioelectrical impedance analysis (BIA) for the screening purpose. All these instruments yield data on muscle mass, but not muscle strength. Unlike in the youth, muscle strength is not necessarily proportional to muscle mass in the elderly due to involutional changes such as increased intramuscular adipocity [7]. Second one is the validity to employ grip strength. Since, age-related decline of muscle strength is more prominent in lower extremity than in the upper extremity [8], grip strength may not be ideal in the diagnosis of sarcopenia. Nevertheless, grip strength has been most frequently used, probably because of its ease and availability. Recently, however, a novel instrument was developed (Locomoscan, Alcare Co. Ltd., Tokyo, Japan) to easily measure quadriceps strength as will be detailed in “Methods” section [9], [10]. Based on these considerations, we have studied the usefulness of leg muscle strength to predict the gait speed which was employed as one of the representative indicators of activity of daily living (ADL).

Based on these considerations, we have considered it worthwhile to compare the usefulness of grip strength and lower leg muscle strength measurement for predicting gait speed, a key component of sarcopenia.

Methods

Subjects

The study subjects were 43 (11 male and 32 female subjects) elderly nursing home residents in a nursing home in Kyoto. They were informed of the study protocol, and written informed consent was obtained. The study protocol was done conforming to the Declaration of Helsinki, and approved by the Ethical Committee in Kyoto Women's University (approval number: 25-20). Written informed consent was obtained from each participant. Subjects with conditions which make the muscle strength measurement difficult such as deformity or paralysis in their extremity were excluded. Those with dementia were also excluded.

Anthropometric and body composition measurement

Height was measured using stadiometer (Seca213, Yagami Inc., Nagoya, Japan). Body weight and body composition was measured with BIA equipment (Karada Scan; Omron HealthCare, Co. Ltd., Kyoto, Japan). Body mass index (BMI) was calculated as body weight (kg) divided by squared height (m).

Measurement of muscle strength

Measurement of muscle strength was done for grip and leg. Grip strength was evaluated according to The Japan Fitness Test. In brief, measurement was performed in an upright position using a hand dynamometer (T.K.K5401, Digital Grip Dynamometer, Takei Scientific Instruments, Niigata, Japan). Leg muscle strength was evaluated using Locomoscan (AllCare Co. Ltd., Tokyo, Japan), which is a recently developed instrument mainly reflecting the quadriceps strength. Subjects lie on a table with one of their legs stretched, push down a pillow located beneath their knee. Then a sensor in the pillow detects the power loaded on it, which mainly represent the quadriceps strength. It is characterized by its easiness to perform, freedom from pain, and short duration of time required [9], [10]. Additionally, muscle strength measured by Locomoscan has reported to be well correlated with that by Biodex (r = 0.82), which is a far larger standard instrument with known accuracy [9]. The results are expressed in kilogram for grip strength and in Newton for leg muscle strength.

Measurement of gait speed

Gait speed was measured in accordance with the instruction in Short Physical Performance Battery [11]. In brief, subjects were asked to walk at their usual speed for 4 m. First, they stand with both feet touching the starting line, walk all the way past the other end of the tape before stop. Gait speed was defined as distance (4 m) divided by the time between the subjects begin walking and when one of the participants' feet is completely across the end line. Results were expressed as the gait speed (m/s).

Statistical analysis

Statistical analysis was done with IBM SPSS Statistics ver. 22.0 (IBM Co., Armonk, NY, USA). Comparison of 2 independent variables was done with Student t-test. Correlation of 2 variables was done with Pearson correlation coefficient. The predictive value of various parameters for gait speed was analyzed by receiver operating characteristic (ROC) curve, the details of which will be described below. Statistical significance was defined as P < 0.05.

Results

Background profiles of the study subjects are shown in Table 1. They were aged 82.9 years as the average with no gender difference. Although men had higher height and weight, BMI was no different. Percentage of fat was lower and that of skeletal mass was higher in men.

Table 1

Background profiles of the study subjects.

Variable	Total (n = 43)	Men (n = 11)	Women (n = 32)	P-valuea
Age, yr	82.9 ± 6.0	82.4 ± 6.5	83.1 ± 5.9	0.733
Height, cm	153.3 ± 8.6	164.2 ± 3.7	149.4 ± 6.1	<0.001
Weight, kg	50.7 ± 9.2	58.8 ± 6.0	47.8 ± 8.4	<0.001
Body mass index, kg/m2	21.5 ± 2.8	21.9 ± 2.5	21.3 ± 3.0	0.610
Fat, %	30.7 ± 6.0	23.4 ± 4.9	33.4 ± 3.8	<0.001
Skeletal muscle, %	23.2 ± 3.3	27.9 ± 2.0	21.6 ± 1.8	<0.001

Values are presented as mean ± standard deviation.

t-test.

According to the diagnostic protocol for sarcopenia by EWGSOP, subjects were categorized into 2 groups; gait speed equal to or greater than 0.8 m/s and that less than 0.8 m/s. As shown in Table 2, leg muscle strength per body weight (N/kg) was significantly greater in those with gait speed equal to or greater than 0.8 m/s, whereas there was no significant difference in the age, grip strength, percentage of skeletal muscle, percentage of fat, and BMI between the 2 groups.

Table 2

Comparison of subjects with gait speed less than 0.8 m/s those equal to or higher than 0.8 m/s.

Variable	≥0.8 m/s (n = 29)	<0.8 m/s (n = 14)	P-valuea
Age, yr	82 ± 2.0	81.5 ± 6.1	0.783
Grip strength, kg	20.7 ± 12.4	20.3 ±± 5.2	0.906
Skeletal muscle, %	23.2 ± 3.6	23.1 ± 3.3	0.901
Fat, %	30.4 ± 6.8	31.9 ± 6.0	0.548
Body mass index, kg/m2	21.7 ± 3.3	21.0 ± 2.0	0.569
Leg muscle strength per body weight, N/kg	5.0 ± 1.4	3.3 ± 1.4	0.003

Values are presented as mean ± standard deviation.

t-test.

Then the predictive value of leg muscle strength for gait speed was analyzed by ROC curve (Fig. 1). In ROC analysis, curve away from the diagonal line, or in other words area under the curve (AUC) higher than 0.5 indicates a good diagnostic value. AUC was 0.731 (95% confidence interval [CI], 0.546–0.916) for the left leg and 0.744 (95% CI, 0.565–0.922) for the right leg. In contrast, other parameters; age, BMI, percentage of skeletal muscle, grasp strength, did not show significant predictability (data not shown). The cutoff value was determined to be 3.65 N/kg body weight by Youden index, in which a value yielding the maximal “sensitivity + specificity – 1” is adopted.

Fig. 1

Receiver operator characteristics (ROC) curve for the prediction of gait speed equal to or faster than 0.8 m/s. Predictive values of various parameters for the gait speed equal to or greater than 0.8 m/s were compared by ROC curve; (a), (b), and (c) stands for leg muscle strength (N/kg weight), grip strength (kg), and percentage of skeletal muscle, respectively.

Discussion

Sarcopenia is an age-related decline in skeletal muscle volume and strength. It is associated with increased mortality and morbidity including increased risk of falling and fracture [12], [13], limitations in ADL [14] and quality of life [6], [9]. Since it is an involutional phenomenon, the number of subjects with sarcopenia is enormous and ever increasing with the aging of the society. For such disorder, prevention is essential. As described in the Introduction, a diagnostic procedure by EWGSOP defines sarcopenia based on gait speed, grip strength, and skeletal muscle volume. Grip strength was employed probably because of its ease to perform. However, we have considered that the appropriateness of grip strength as the screening parameter for sarcopenia must be reconsidered based on several reasons. First, grip strength decreases with aging, which, however, is far less marked than that of leg muscle [8]. Therefore, grip strength may not be a suitable index for sarcopenia. Second, risk of falling would be more related to leg muscle strength than grip strength.

In our analysis, lower leg muscle strength was lower in those with slower gait speed than those with higher gait speed, whereas no significant differences were observed between the 2 groups in other parameters including age, grip strength, percentage of skeletal muscle, percentage of fat and BMI.

Additionally, ROC analyses have shown that lower leg muscle strength well predicted gait speed equal to or higher than 0.8 m/s, whereas other parameters did not. These results suggest that lower leg muscle strength is a good indicator for the ADL of the elderly and possibly can be a sensitive screening tool for sarcopenia now that such instrument to measure it easily has become available.

Our study has some limitations. First, the number of study subjects was only modest, since the capacity is rather limited in most Japanese nursing homes and subjects with impaired recognition were excluded. Additional study including more subjects and more nursing homes is planned. Second, the usefulness of leg muscle strength measurement was validated against the gait speed. Gait speed is, needless to say, a good indicator of ADL, and an important parameter in the diagnosis of sarcopenia. However, validation with more clinically oriented outcomes is more favorable [15]. Additionally, since this is a retrospective observational study, confounding factors could not be excluded. Therefore, validation with such indices as mortality or falling incidence in a cohort study is needed [13]. Despite these limitations, we believe that our paper has clinical implications, since the usefulness of leg muscle strength measurement in the diagnosis of sarcopenia has not been published before.

Conclusions

We have reported that lower leg muscle strength well predicted gait speed, and suggested the possible usefulness of its measurement in the diagnosis of sarcopenia.

Conflicts of interest

No potential conflict of interest relevant to this article was reported.