Relationships between Tongue and Lip Movement and Physical Fitness among Independent Community-Dwelling Elderly in Japan

Aim: The present study aims to examine the association between tongue and lip movement and physical fitness with a sample of independent community-dwelling elderly. Methods: A total of 119 older adults living in a city of Japan participated in this study. Tongue and lip movement was evaluated with oral diadochokinesis (ODK) rate for the syllable “pa”, “ta”, and “ka” measured by counting syllable repetitions within one second. Physical fitness was objectively evaluated with the Timed-Up and Go Test (TUG) and the 30-Second Chair Stand Test (CS-30). Subjective physical fitness was also assessed with a Physical Component Summary score (PCS) of the 36-item Short-Form Health Survey (SF-36). Partial correlation coefficients between ODK rates and physical fitness measures were obtained after adjusting the effects of age and the number of present teeth. Results: There were significant differences in ODK rates for the syllable “ta” and “ka” between the participants aged 65 74 and 75 or older. Significant differences in all the physical fitness measures were also observed in the two age groups. Partial correlation analysis with age and number of present teeth as covariates yielded significant correlations of ODK rates to TUG and PCS, but not with CS-30. Conclusion: Older adults whose functional mobility declined tended to maintain the movement of tongue and lips. Moreover, those who perceived declining physical fitness also tended to show a decline of tongue and lip movement. Thus, the present study added some knowledge on the relationships between general physical fitness and tongue and lip movement. It also made several suggestions for future interventions based on the findings. How to cite this paper: Ouchi, J., Hayashi, Y., Matsubara, M., Fukura, K., Miyata, K. and Yamamoto, M. (2020) Relationships between Tongue and Lip Movement and Physical Fitness among Independent Community-Dwelling Elderly in Japan. Advances in Aging Research, 9, 32-44. https://doi.org/10.4236/aar.2020.92004 Received: January 24, 2020 Accepted: February 25, 2020 Published: February 28, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access


Introduction
The population is rapidly aging in Japan, even though it has attained one of the longest life expectancies in the world. Notably, Japan's healthy life expectancy has not extended similarly to its life expectancy [1]. More endeavors are needed so that the elderly can maintain their functioning and independence.
Recent arguments emphasize the importance of oral function as a critical factor to keep older adults functional and independent [2] [3]. The oral function is essential not only in terms of verbal communication but also concerning the intake of adequate nutrition. Malnutrition leads to sarcopenia or the decline of skeletal muscle tissue and function with age [4]. Because sarcopenia is one of the most significant causes of functional decline and loss of independence in older adults [4], a proper oral function is essential for the elderly to remain functional and independent.
Among various aspects of oral function, such as occlusal force and saliva flow, the present study focused on tongue and lip movement because of its importance in ingesting and processing foods [5]. Research often uses oral diadochokinesis (ODK) to evaluate the dexterity of tongue and lip movement [2] [6]. It requires an individual to repeatedly produce strings of syllables as fast as possible in a certain period, such as five seconds [6]. ODK rate for the individual is obtained by calculating the number of articulated syllables per unit time, such as one second [6]. Syllable "pa", "ta", and "ka" are often utilized for Japanese samples [7]. ODK for the syllable "pa" represents lip movement, whereas ODK for the syllable "ta" and "ka" represents the movement of the dorsum of the tongue [8].
In research conducted in Japan with samples of independent older adults, mean ODK rates range between 5 to 7 per second [6] [7] [8] [9], whereas those ranging 4 to 5 per second in research with samples of older adults needed help for activities of daily living [10] [11]. Research also suggests ODK rate declines with age [6] [7] [8] [9].
In addition to functional decline and aging, general physical fitness may be significantly associated with tongue and lip movement in older adults. Izuno et al. [6] examined associations between ODK and five measures of physical fitness with a sample of 66 independent community-dwelling elderly. In that study, mean ODK rates for syllable "pa", "ta", and "ka" ranged from 6.3 to 6.9 for the participants aged 65 -69, and from 5.2 to 6.3 for those aged 70 or older. They reported significant associations between ODK for the syllable "pa" and functional mobility, ODK for the syllable "ta" and lower body flexibility, and ODK for the syllable "ka" and grip strength as well as balance ability. They concluded Advances in Aging Research that tongue and lip movement was associated with physical fitness. However, they suggested that more examinations with larger samples are needed to gain insights on associations between tongue and lip movement and physical fitness.
Watanabe et al. [8] compared the ODK rate among robust, prefrail, and frail older people with a large sample in Japan. The study assigned 4720 community-dwelling elderly into three groups, namely the robust, prefrail, and frail group. The frailty phenotype was decided according to five domains of physical fitness, including mobility, strength, endurance, physical activity, and nutritional status. The results denoted that the frail group had a significantly lower ODK rate than the robust group. The study also examined influences of age on tongue and lip movement by comparing ODK rates among four age groups: 65 -69, 70 -74, 75 -79, 80 or older. They reported that ODK rates declined with age, suggesting deteriorations of tongue and lip movement with age. Their findings suggest significant associations between tongue and lip movement and physical fitness. However, they did not directly investigate associations between specific physical fitness measures and tongue and lip movement. Further investigations are, therefore, needed to know what aspects of physical fitness have significant associations with tongue and lip movement.
It is valuable to understand relationships between tongue and lip movement and physical fitness in terms of preventing loss of independence in community-dwelling elderly. Such preventive interventions in Japan frequently include exercise aimed at promoting motor functions contributing to physical fitness [12] [13]. If physical fitness is significantly associated with tongue and lip movement, such interventions may work for promoting oral function as well.
Moreover, it becomes easier to identify older adults who may have some problems in eating and swallowing before examination of oral function, provided the associations are significant. Concerning the issue mentioned above, the present study also examined associations between tongue and lip movement and subjective physical fitness to explore the effectiveness of an elderly's perceptions of physical fitness on detecting a decline in tongue and lip movement.
In summary, the present study aimed to examine relationships between tongue and lip movement and physical fitness in independent community-dwelling elderly in Japan.

Participants
People aged 65 years or older who lived in a residential area of an urban city in Hokkaido, Japan, were recruited as participants for a survey held on a university campus located in the city in March 2018. They were informed of the survey by flyers circulated through the community centers of that area.

Data Collection
Oral diadochokinesis was measured to assess tongue and lip movement. Partici- pants were asked to articulate the "pa" syllable repetitively as quickly as possible for 5 seconds. The number of articulations was counted with an automatic counter (T.K.K.3351 digital counter, Takei Scientific Instruments Co. Itd., Nigata city, Nigata, Japan). The same procedure was repeated for syllables "ta" and "ka". The average number of articulations per second for "pa", "ta", and "ka" were respectively calculated as the ODK rate for each syllable.
Objective physical fitness was evaluated in terms of lower limb strength and functional mobility. Lower limb strength was assessed with a 30-Second Chair Stand Test (CS-30) [14]. The test was started at the posture of participants sitting on the chair with both limbs spread to the width of the shoulder, separated the back from the backrest, and the arms were assembled in front of the chest. The participants were then asked to rise and sit on a chair repeatedly as quickly as possible within 30 seconds. subscale score can range from 0 to 100. A higher score means a higher level of health-related QOL. In this study, the PCS score was used to assess participants' subjective physical fitness. It was calculated by an algorithm provided by iHope International Corporation after raw scores of the subscales were standardized using means and standard deviations from the general Japanese population provided by the same company. The mean PCS for people aged 60 -69 and 70 -79 gained from the general Japanese population are respectively 46.9 ± 11.6 and 42.1 ± 14.6 regardless of sex [17].
Participant demographic information including age, gender, family structure, form of living, and regular hospital visit was collected with a self-administrated questionnaire. Participants were also asked about the number of outings per week as an indicator of their activity. Their level of instrumental activities of daily living (IADL) was assessed as an indicator of physical, cognitive, and social function by the Rouken-Shiki scale [18]. This 13-item scale was developed in Japan and ranged from 0 to 13, with a lower score indicating poorer IADL. Nutri-

Data Analysis
All data were statistically analyzed with SPSS statistics 24 (IBM, Armonk, NY, USA). First, to explore age differences in ODK rate and physical fitness measures, participants were divided into two groups: 65 -74 (≤74 age group) and 75 years or older (≥75 age group). Such age classification was thought to be meaningful because healthcare and welfare policies for the elderly in Japan are developed based on those age groups. Then, influences of age and sex on ODK rates and physical fitness measures were examined by two-way analysis of variance (ANOVA). Sidak test was conducted as a post-hoc test when the main effects of either age or sex were significant. Finally, partial correlation coefficients were obtained to examine relations between ODK rates and physical fitness measures independent of covariates: age and number of present teeth.

Ethical Consideration
Approval of the protocol was obtained from the Institutional Review Board at the authors' affiliated university (IRB No. 206) in February 2017. Verbal and written informed consents were obtained from individual participants.

Participant Characteristics
One hundred nineteen older adults participated in this survey. Participant characteristics are shown in

Oral Diadochokinesis
Means and standard deviations of the ODK rate for the three syllables in all, female, and male participants in the two age groups are shown in Table 2. Data on the ODK rate was almost normally distributed. There was no sex difference in means of ODK rate for the syllable "pa" (P = 0.41), "ta" (P = 0.98), and "ka" (P = 0.50). On the other hand, means of ODK rate for the syllable "ta" (P = 0.01) and "ka" (P = 0.01) in the ≤74 age group was higher than the ≥75 age group.  However, no significant difference was found in the ODK rate for the syllable "pa" between the age groups (P = 0.12). Table 2 also presents means and standard deviations of the physical fitness measures for all, female, and male participants in the two age groups. Data of each physical fitness measure was also almost normally distributed. Between female and male participants, there were no significant differences in mean scores of all the measures: CS-30 (P = 0.70); TUG (P = 0.83); PCS (P = 0.66). On the other hand, significant age differences in means were observed in all the measures. The mean of CS-30 in the ≤74 age group was significantly larger than the ≥75 age group (P = 0.01). Similarly, the ≤74 age group has a shorter mean TUG time compared with the ≥75 age group (P = 0.002). In addition to these objective physical fitness measures, a mean PCS score for the ≤74 age group was significantly higher than one for the ≥75 age group (P = 0.02).

Associations between ODK and Physical Fitness
Prior to partial correlation analysis, intercorrelations for participant characteristics, ODK rate, and physical fitness measures were explored ( Table 3). As the table shows, age was significantly associated with ODK rate for the syllable "ta" (P = 0.004) and "ka" (P = 0.014) as well as all the physical fitness measures: CS-30 (P = 0.004); TUG (P = 0.001); PCS (P = 0.01). However, it was not related to the ODK rate for the syllable "pa" (P = 0.15). In addition to age, the number of present teeth had significant associations with ODK rate for the syllable "ta" (P = 0.001) and "ka" (P = 0.001) but not with that for the syllable "pa" (P = 0.07).
Number of present teeth was also significantly associated with CS-30 (P = 0.002) and TUG (P = 0.008) but not with PCS (P = 0.94). Gender was associated only with the ODK for the syllable "ka" weakly but not with the ODK for the syllable "pa" (P = 0.08) and "ka" (P = 0.16) as well as any of the physical fitness measures: CS-30 (P = 0.12); TUG (P = 0.24); PCS (P = 0.52).
Based on the results above, partial correlation coefficients between ODK rate and physical fitness measures were obtained with age and the number of present teeth as covariates ( Table 4). As it illustrates, no significant association was found between CS-30 and ODK rate for all the syllables: "pa" (P = 0.05); "ta" (P = 0.22); "ka" (P = 0.39). TUG had a significant but weak association with ODK rate for the syllable "pa" (P = 0.048) and "ta" (P = 0.02) but not with ODK rate for syllable "ka" (P = 0.06). On the other hand, PCS had significant associations with ODK rate for all the syllables: "pa" (P = 0.001); "ta" (P < 0.001); "ka" (P = 0.002).

Discussion
The present study investigated associations between tongue and lip movement and physical fitness with a sample of community-dwelling independent older adults. Results suggested that tongue and lip movement was significantly associated with functional mobility and subjective physical fitness even after adjusting the effects of age and number of present teeth.
Participants in the present study could be characterized as being generally healthy, functional, and active even most of them visit clinic(s) or hospital(s) regularly. Results of BMI, as well as the number of present and functional teeth, indicated that they generally stayed in good nutritional status and oral condition. The mean score of the IADL scale in the present study was close to its maximum score, suggesting they were adequately functional to live independently. Also, most participants regularly outed more than 3 times a week, and nearly half of them outed more than 5 times a week, suggesting that they had a relatively active lifestyle.
Results also suggested that participants in the present study were average in physical fitness. Results of CS-30 indicated that the participants had average lower limb strength based on standard scores proposed by Nakatani et al. [14]. Results of TUG were also similar to results from past literature [19], suggesting that the participants had average functional mobility compared to their counterparts. On the other hand, the results of PCS suggested that participants in the present study had a slightly higher level of subjective physical fitness compared with the reference scores that Fukuhara and Suzukamo [17] presented, even though age classification was different between the studies. Thus, the participants in this study were thought to be generally and physically -healthy and functional.
Mean ODK rates in the present study were similar to results from past studies [7] [8]. Results on the associations between age and ODK for the syllable "ta" and "ka" indicated that tongue movement declines with age among independent older adults. This deterioration is consistent with findings from past studies examining the influences of age on oral function [6] [7] [8]. Such deteriorations in tongue movement may be related to decreases in tongue thickness and muscle strength with age observed in previous studies [20] [21].
In contrast, ODK for syllable "pa", which represents lip movement, was not affected by age in the present study. This finding is inconsistent with results from past literature reporting that ODK for the syllable "pa" also declined with age [6] [7] [8]. This decline may be due to the distinctions in age classifications between the studies. For example, Watanabe et al. [8] classified participants into four age groups and observed differences between them, while the present study divided those into two. It was believed that a smaller age classification would make it easier to detect age-dependent effects. Another possible reason for the inconsistency is that lip movement is less likely to be affected by age compared to tongue movement. In the present study, the correlation analysis yielded no significant linear association between age and ODK rate for the syllable "pa".
This result is consistent with findings from Watanabe et al. [8]. In their study, both of the 70 -74 and 75 -79 age groups had the same means and standard deviations of ODK for the syllable "pa". Both findings indicated no linear association between age and ODK for the syllable "pa", suggesting that lip movement can be stable while people are getting old. Past literature has rarely focused on the difference in age-dependent changes between tongue and lip movement.
Further examinations are required to address this issue adequately.
In addition to age, the number of present teeth was significantly associated with ODK rates for all the syllables in the present study. The number of present teeth is a cardinal indicator of oral health condition [22]. Eklund and Burt [22] also reported that oral health was affected by the patients' cumulative disease experience and treatments chosen. The findings indicate that maintaining good oral and general health contributes to a higher number of present teeth as well as better tongue and lip movement.
Results of the partial correlation analysis yielded significant associations be-  [24]. Such effective exercise programs may be able to show their effectiveness in promoting tongue and lip movement if the functional ability is significantly associated with it. Such application of exercise programs to promote the oral function in older adults is vital in terms of cost and resource-saving for long-term care prevention efforts in super-aged societies, such as Japan. It would also be efficient for older people, as they do not need to attend multiple intervention programs.
Thus, the results of the present study suggest that tongue and lip movement is associated with physical fitness. Some suggestions were also discussed based on the findings for future interventions targeting independent community-dwelling elderly. However, there is still a dearth of knowledge on relationships between Moreover, whether the findings can be applied to those with loss of independent and/or hospitalized ones because the participant in the present study was independent and relatively healthy. Also, it is still unknown whether interventions aimed at promoting motor functions facilitate tongue and lip movement.
Therefore, future studies should have a longitudinal research design with multiple measures of tongue and lip movement with both samples of older adults with different functional and health levels.

Conclusion
The present study found that tongue and lip movement was associated with functional mobility and subjective physical fitness in independent community-dwelling elderly. It was also suggested that when older adults perceived a decline in physical fitness, their tongue and lip movement also tended to decline.
This decline may contribute to an early awareness of declining tongue and lip movement by healthcare professionals as well as older adults by themselves.
Moreover, effective exercise programs aimed at promoting motor functions may work for retaining tongue and lip movement in the elderly.