Effects of Whole-Body Vibration Training on Improving Physical Function, Cognitive Function, and Sleep Quality for Older People with Dynapenia in Long-Term Care Institutions: A Randomized Controlled Study

Abstract

As the global demographic shifts toward an aging population, aging-related problems, particularly in older individuals with dynapenia, are increasingly gaining attention. However, interventional studies focusing on physical and cognitive function and sleep quality in such individuals are limited, indicating a need for further exploration. The present study investigated the effects of whole-body vibration (WBV) training on physical and cognitive function and sleep quality in older people with dynapenia residing in long-term care institutions. This study was a randomized controlled trial. The experimental group underwent WBV training three times a week for 3 months, whereas the control group continued with their regular daily care routine. Statistical analyses were performed using the Traditional Chinese version of SAS Statistics version 9.4. Paired t tests, a one-way analysis of variance, independent t tests, and generalized estimating equation analysis were performed. The results revealed that compared with the control group, the experimental group experienced significant improvements in grip strength, instrumental activities of daily living, cognitive function, and sleep quality in terms of latency and duration. These findings suggest that 3 months of WBV training can effectively enhance physical and cognitive function and sleep quality in older people with dynapenia residing in long-term care institutions.

1. Introduction

According to the World Health Organization (WHO), the global population is currently experiencing an aging trend, with the number of individuals aged 60 years or older estimated to increase from approximately 900 million (12%) in 2020 to 2 billion (22%) by 2050 [1]. In response, the WHO has established a set of goals called “Active Aging and Disability Prevention” to address the challenges of an aging population [1]. In Taiwan, the percentage of the population aged 65 years and older reached 14.05% in 2018, marking the transition to an “aged society”. By 2025, older individuals are projected to constitute 20.1% of the population, leading to Taiwan becoming a “super-aged society” [2].

Aging refers to the physiological process of growing older, characterized by declines in memory and physical strength and the gradual deterioration of bodily functions. As humans age and their muscle strength decreases, the likelihood of developing dynapenia increases [3]. Kobayashi et al. [3] defined dynapenia as the presence of normal muscle mass accompanied by a reduction in muscle strength or function, which adversely affects physical function and the capacity for physical activity. Noh and Park [4] conducted a survey of 2652 older community members in Korea and defined dynapenia as having handgrip strength (HGS) below 26 kg for men and below 18 kg for women. They observed that 25.1% of the older participants had dynapenia. Furthermore, Tessier et al. [5] assessed dynapenia in 51,388 male and female residents aged 45–86 years from a Canadian community by performing HGS, gait speed, sit-to-stand, and balance tests. Their findings revealed that 21.5% of the men and 13.7% of the women exhibited signs of dynapenia.

Tessier et al. [5] also reported that the dynapenic population is at high risk of disability, which compromises physical activity function, leads to related complications, and increases the risk of mortality. Aging, a dynamic and progressive process, negatively affects the independence and life functions of older individuals. A study involving 123 community-dwelling older individuals aged 65 years and older assessed physical function and instrumental activities of daily living (IADLs) and found that patients with dynapenia had poorer physical function than those without dynapenia (odds ratio [OR] = 2.01, 95% confidence interval [CI]: 1.43–1.53, p < 0.05) [6]. Furthermore, increasing age is associated with declines in broad cognitive functions, including memory, attention, and executive functions [7]. In addition, the dynamic and progressive nature of aging leads to gradual reductions in independence and quality of life among older individuals, resulting in mild cognitive impairments and decreased memory and learning abilities, and thus affecting their IADLs [8].

Sleep disorders in older individuals have long been a concern given that sleep quality is closely related to overall health. Poor sleep quality is a common problem among older people with dynapenia. Skottheim et al. [9] assessed sleep quality in older residents of Swedish long-term care facilities and found that the incidence of insomnia was as high as 50%. The most common sleep problems included nighttime awakenings, early morning awakenings, and prolonged daytime sleep. In addition, these older individuals often reported sleep problems, experienced decreases in total sleep duration and deep sleep phases, and encountered increased sleep interruptions. In these patients, deep sleep comprised only 5%–10% of total sleep. The Taiwan Society of Sleep Medicine conducted a survey titled “Trends in the Prevalence of Common Sleep Problems in Taiwan”. The results indicated that the prevalence of insomnia in Taiwan was 11.3%, with approximately 1 in 10 people experiencing severe insomnia. Among these individuals, 16.7% of those aged 50–59 years and 22.7% of those aged 60–69 years experienced insomnia [10]. Lin et al. [11] determined a correlation between age and sleep quality among older people with dynapenia, with older age being associated with poorer sleep quality.

Vertical stimulation training is increasingly being used as an intervention to enhance the health of older individuals. This form of training provides benefits similar to traditional resistance training but also offers greater safety and convenience, reducing the risk of injury associated with resistance exercises in older adults. Lin et al. [11] conducted a randomized controlled trial (RCT) involving 54 community-dwelling individuals 65 years and older with mild cognitive impairments. Over a period of 9 weeks, the participants received vibration training at an amplitude of 2 mm and a frequency of 30 Hz, whereas the control group continued with their regular community home activities. The results indicated substantial improvements in muscle strength and balance scores among those who had undergone the vibration training. Furthermore, Lai [12] performed a systematic review and meta-analysis to compare the effects of vibration training, resistance training, and endurance training interventions on muscle strength and physical activity function in older individuals. That meta-analysis included 31 RCTs involving 1405 participants aged 65 years and older. The results demonstrated that vibration training significantly enhanced functional performance in older individuals, resulting in improvements in HGS, one-leg balance, shoulder-arm flexibility, walking speed, and the ability to perform the sit-to-stand test five times.

The aforementioned findings indicate that aging adversely affects physical and cognitive function and sleep quality. However, although many studies have focused on these problems among older individuals, studies investigating specific interventions to help older people with dynapenia residing in long-term care facilities remain limited.

Aim

This study investigated the effect of whole-body vibration training on physical and cognitive function and sleep quality in older people with dynapenia residing in long-term care facilities.

2. Methods

2.1. Research Design

This study was designed as an RCT in which patients residing in various long-term care facilities were randomly assigned to an experimental group and a control group. The experimental group underwent 3 months of a whole-body vibration (WBV) training intervention, whereas the control group continued to receive their regular daily life care. After the 3-month intervention, the physical and cognitive function and sleep quality of the participating patients were evaluated.

2.2. Participants

This study adopted the dynapenia criteria proposed by Kobayashi et al. [3] for Asian older individuals. These criteria include initial assessments of muscle function, including grip strength (≤26 kg for men and ≤18 kg for women indicates low grip strength) and walking speed (0.8 m/s indicates slow speed). Either or both of these indicators were used together with skeletal muscle mass (≥7.0 kg/m² for men and ≥5.7 kg/m² for women) to diagnose dynapenia.

We used G-Power 3.1.9.4 software to calculate the required sample size, with a Cronbach’s α of 0.05 and a power of 0.80 [13]. Following a previous study [14], the effect size was set at 0.4. We determined that both groups should contain at fewest 58 participants.

The inclusion criteria for the participants are described as follows: (1) skeletal muscle mass of limbs of ≥7.0 kg/m² for men and ≥5.7 kg/m² for women; HGS of <26 kg for men and <18 kg for women; walking speed of >0.8 m/s; age of 65 years or older and residing in a nursing facility without any contraindications for physical activity. (2) Consciousness and the ability to communicate in Mandarin or Taiwanese and follow commands. (3) Willingness to participate in this study and to sign the informed consent form after receiving an explanation of the research purpose.

The exclusion criteria for participants are described as follows: (1) acute injury, including fracture or hip or knee joint damage, or surgery within the preceding 1 month; (2) presence of severe heart disease (including the presence of a heart stent or receipt of bypass surgery), coronary artery disease, or a pacemaker; (3) diagnosis of a communicable disease or mental illness; and (4) severe visual or auditory impairment that could affect their ability to undergo testing.

2.3. Research Tools

2.3.1. Body Composition

We measured the muscle mass of the older participants by using a bioelectrical impedance analysis (BIA) device (Danilsmc, model ioi353). This device can assess the muscle (skeletal muscle) and fat mass of both arms, both legs, and the trunk and is suitable for use among both community-dwelling and institutionalized older populations. Kobayashi et al. [3] conducted a study on Japanese community-dwelling older individuals and determined that the same BIA device could effectively identify dynapenic individuals. The test requires only 5–10 min, thereby providing a cost-effective, fast, convenient, and nonradiative diagnostic tool. A study that used the same BIA device to assess visceral fat, body fat, and muscle mass in 95 athletes demonstrated the device’s high reliability with a Cronbach’s α of 0.91 [15].

In the present study, during measurements, the participants were asked to stand barefoot on the metal plates of the BIA device, hold sensor-equipped handles with both hands, and keep their arms naturally apart to prevent contact under the armpits while waiting for the results. The BIA device can measure muscle and fat content and is portable, making it ideal for use in institutional settings [16]. The present study used a bioelectrical impedance analyzer that sends electric currents through local muscles to collect data. Akamatsu measured resistance in the upper arm at 50 kHz and observed that muscle and fat values were highly correlated with computed tomography values, with a minimal average error [16]. Furthermore, a study comparing BIA (50 kHz and 800 µA, RJL) with radioactive DEXA for detecting body cell mass, fat-free mass, and total body water in both patients with and without HIV found that BIA could effectively detect body composition. This finding indicates the suitability of the aforementioned BIA device for clinical and research use and for long-term tracking [17].

2.3.2. Walking Speed Measurement

A 2.44-m walking speed test was conducted to assess the dynamic balance ability of the older participants. In this test, each participant started seated in a chair. Upon hearing a signal, they were required to stand, walk forward 2.44 m, circle around a marker pole, and then return to the chair to sit back down. The total time required to complete this action was recorded. This test was designed to assess both the participants’ agility and dynamic balance capabilities. The intraclass correlation coefficient for this walking speed test was 0.99 [5].

2.3.3. Demographic Characteristics

We collected information regarding the following demographic characteristics: sex, age, educational level, religious beliefs, marital status, smoking history, alcohol-consumption history, and medical history.

2.4. Physical Function

2.4.1. HGS

We used an electronic handheld dynamometer (Charder, MG4800) to measure grip strength. According to Lee et al. [15], this dynamometer had a test–retest reliability of 0.98, and the MG4800 was validated against Jamar dynamometers, demonstrating a high correlation (r = 0.954, p < 0.05). In the present study, during measurement, the tester instructed each participant to grip the dynamometer handle while keeping both shoulder joints in a neutral position and their arms hanging naturally at the sides. After a start command, the participant was asked to squeeze the handle as tightly as possible for approximately 5 s. Grip strength was measured three times for each hand, and the highest recorded value was used to represent the participant’s peak performance for the test.

2.4.2. IADLs

IADLs are defined as tasks that require interaction with the external environment and involve the management of cognitively complex activities necessary for independent living. Such activities include using the telephone, shopping, participating in outdoor activities, cooking, using public transportation, performing household chores, doing laundry, managing medications, and handling finances. These tasks are essential indicators for assessing the independence of community-dwelling older individuals [18]. Siriwardhana et al. [8] measured IADLs in 702 community-dwelling older individuals aged 60 years and older in Sri Lanka and achieved considerably high internal consistency (Cronbach’s α = 0.91) and inter-rater reliability, indicating high consistency across all IADL items, with overall correlations for IADL scores ranging from 0.57 to 0.91.

2.5. Cognitive Function

We used the Mini-Mental Status Examination (MMSE) as a diagnostic tool to screen for cognitive function. Originally developed by Folstein and colleagues in 1975, the MMSE is a widely used test with high reliability (Cronbach’s α = 0.83) that evaluates cognitive domains through 11 items—covering orientation, registration, attention and calculation, recall, and language—with a maximum score of 30. Scores ranging from 24 to 30 indicate intact cognitive function, those of 18 to 23 indicate mild cognitive impairment, and those of 0 to 17 indicate severe cognitive impairment. Siriwardhana et al. [8] used the MMSE to assess 163 patients with end-stage renal disease, setting the cutoff for cognitive impairment at ≤21 points. When compared with the Montreal Cognitive Assessment, the MMSE demonstrated higher sensitivity (77.46%), specificity (72.83%), and reliability (Cronbach’s α = 0.74).

2.6. Sleep Quality

We used the Pittsburgh Sleep Quality Index (PSQI), developed by Buysse et al. [19], to assess sleep quality. The PSQI is a questionnaire consisting of nine questions, with the fifth question divided into 10 subquestions. This tool measures seven components of sleep: subjective sleep quality, sleep latency, total sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction. Each component is rated on a scale ranging from 0 to 3, with the total score ranging from 0 to 21. A cumulative score higher than 5 indicates poor sleep quality, whereas a score of 5 or lower indicates good sleep quality. That is, a higher score corresponds to poorer sleep quality. Sun et al. [20] examined the sleep quality of 1726 community-dwelling older individuals aged 70–87 years and demonstrated that the PSQI was effective for assessing sleep disorders in this older population. That study observed a correlation between sleep quality and age, with a Cronbach’s α of 0.83 and test–retest reliability scores ranging from 0.77 to 0.85.

2.7. Whole Body Vibration Training

This study involved whole-body vibration (WBV) training for older adults with dynapenia in the experimental group. A vibrational platform (Bw760B, Taipei City, Taiwan) was used for the vibration training. The research was based on the parameters identified by Lin et al. [21], which include a vibration frequency of 25–40 Hz and an amplitude of 2.5–5 mm. Each training session consisted of 60 s of vibration followed by 30 s of rest, repeated 10 times, and was conducted at least three times per week. This protocol is designed to enhance muscle contraction, improve muscle strength, and boost muscle function in older adults. Consequently, the experimental group followed this intervention program for a duration of 3 months.

2.8. Statistical Analysis

Data were collected using a structured questionnaire, and the collected data were analyzed using the traditional Chinese version of the SAS Statistics software suite, version 9.4. The analysis incorporated both descriptive and inferential statistical methods.

In this paper, descriptive statistics (basic demographic data) are presented as the sample size (N), percentages, maximum values, minimum values, mean values, and standard deviations. Regarding inferential statistics, the chi-squared test and independent-samples t tests were conducted to determine differences between the two groups. In addition, paired-samples t tests were performed to determine differences in variables before and after the tests within the same group. A p value of <0.05 was considered statistically significant.

Finally, a generalized estimating equation (GEE) was used to analyze the longitudinal effectiveness of the intervention. Differences in physical and cognitive function and sleep quality following 3 months of WVB training between the two groups were examined.

2.9. Ethical Considerations

This study was approved by the Institutional Review Board (IRB) of Taipei City Hospital (IRB number: TCHIRB-11105007-E). The RCT protocol was registered with the ClinicalTrials.gov Protocol Registration and Results System (OMB no: 0925-0586). Individuals deemed eligible for participation were provided with detailed explanations, and a signed informed consent form was obtained from each of the participants prior to their inclusion in this study.

Finally, to ensure the privacy of all the participants, all data collected in this study were anonymized and coded. Only the researchers had access to the list of participant names. The questionnaire data were used solely for academic research purposes, and no personal data were disclosed publicly.

3. Results

3.1. Homogeneity Testing of Basic Data, Physical Function, Cognitive Function, and Sleep Quality in the Experimental and Control Groups

The results of the chi-squared test revealed no significant pretest differences in sex, age, educational level, religious beliefs, or disease categories between the experimental and control groups (p > 0.05). This finding indicated that the two groups were homogeneous in terms of physical and cognitive function and sleep quality before the intervention commenced (

Table 1. Homogeneity testing of baseline characteristics, physical function, cognitive function, and sleep quality between experimental and control groups in elderly individuals with dynapenia.

Variable		Experimental (n = 29)		Control (n = 29)
		n	%	n	%	t-Value	p-Value
Gender						0.065	0.800
	male	12	41.14	14	48.28
	female	17	58.86	15	51.72
Age						0.161	0.096
	65–74 years old	21	72.41	18	62.07
	75–84 years old	6	20.69	9	31.03
	85 years old and above	2	6.90	2	6.90
Education level						2.500	0.475
	uneducated	9	31.04	7	24.14
	educated	20	68.96	22	75.86
Religious beliefs						3.500	0.321
	None	8	29.03	6	22.58
	Yes	21	70.97	23	77.42
Disease categories						2.500	0.475
	Respiratory System	8	27.59	4	13.56
	Musculoskeletal System	3	10.59	5	17.13
	Circulatory System	8	27.59	8	27.48
	Endocrine Metabolism	10	34.23	12	41.83
		Mean ± SD		Mean ± SD		t-value	p-value
Physical function
	Grip Strength (Right Hand)	24.84 ± 4.48		24.69 ± 4.49		0.439	0.115
	Grip Strength (Left Hand)	22.42 ± 3.82		22.94 ± 3.91		0.461	0.417
IADL
	Shopping Outdoors	1.84 ± 0.69		1.84 ± 0.58		0.229	0.080
	Going Out for Activities	1.81 ± 0.83		1.65 ± 0.71		0.176	0.060
	food preparation	1.74 ± 0.68		1.58 ± 0.67		0.194	0.200
	household maintenance	1.84 ± 0.74		1.57 ± 0.69		0.190	0.070
	laundry	1.71 ± 0.59		1.55 ± 0.67		0.221	0.070
	telephone use	1.61 ± 0.56		1.61 ± 0.56		0.229	0.300
	medication administration	1.65 ± 0.49		1.61 ± 0.50		0.263	0.081
	financial management	1.55 ± 0.51		1.36 ± 0.49		0.228	0.600
Cognitive function
	Sense of orientation	7.71 ± 0.53		8.23 ± 0.56		1.046	0.406
	attention and calculation abilities	3.36 ± 0.88		3.03 ± 0.75		0.304	0.140
	memory	1.65 ± 0.55		1.97 ± 0.61		0.239	0.070
	language	2.10 ± 0.65		2.39 ± 0.67		0.264	0.500
	verbal comprehension	2.32 ± 0.60		1.74 ± 0.63		0.237	0.080
	constructional ability	0.97 ± 0.18		0.74 ± 0.45		0.190	0.090
Sleep quality
	Subjective sleep quality	1.32 ± 0.65		1.39 ± 0.62		0.169	0.905
	sleep onset latency (minutes)	1.32 ± 0.75		1.32 ± 0.65		0.149	0.603
	sleep duration (hours)	1.65 ± 0.61		1.32 ± 0.65		0.181	0.800
	sleep efficiency (%)	1.39 ± 0.76		1.65 ± 0.61		0.172	0.100
	sleep disturbances (minutes)	1.16 ± 0.82		1.26 ± 0.58		0.135	0.060
	use of sleep medication	1.45 ± 0.93		1.23 ± 0.62		0.134	0.180
	daytime dysfunction (minutes)	0.87 ± 0.67		1.16 ± 0.69		0.116	0.360
	total score	9.16 ± 5.19		9.84 ± 4.41		0.151	0.430

p < 0.05.

).

3.2. Analysis of Physical Function, Cognitive Function, and Sleep Quality before and after the Intervention in the Experimental and Control Groups

No adverse events were reported during the intervention period. Our results revealed that HGS significantly increased in both the right hand (paired t = −1.252, p < 0.001) and left hand (paired t = −1.225, p < 0.001) in the experimental group after the intervention compared with before the intervention. In terms of IADLs, the experimental group exhibited significant improvements in their abilities to shop (paired t = −3.50, p = 0.002), participate in outdoor activities (paired t = −2.68, p = 0.012), and manage medications (paired t = −4.35, p = 0.001) after the intervention compared with before the intervention. Furthermore, regarding cognitive function, the experimental group exhibited significant improvements in attention (paired t = −7.84, p < 0.001), calculation ability (paired t = −1.42, p < 0.001), and memory (paired t = −5.30, p < 0.001) after the intervention compared with before the intervention. Finally, regarding sleep quality, the experimental group exhibited significant improvements in sleep latency (paired t = 2.68, p = 0.012) and sleep duration (paired t = 4.06, p = 0.001) after the intervention compared with before the intervention. By contrast, no significant differences in physical or cognitive function or sleep quality were noted in the control group after the intervention compared with before the intervention (

Table 2. Preintervention–postintervention differences in physical function, cognitive function, and sleep quality in the experimental and control groups (n = 58).

Variables			Experimental Group (n = 29)			Control Group (n = 29)
			Mean ± SD	Paired t	p-Value	Mean ± SD	Paired t	p-Value
Physical Function
Grip strength
	Grip Strength (Right Hand)	Pre-test	24.84 ± 4.48	−1.252	<0.001 ***	24.70 ± 4.49	1.603	0.060
		Post-test	26.62 ± 4.53			25.67 ± 4.75
	Grip Strength (Left Hand)	Pre-test	22.42 ± 3.82	−1.225	<0.001 ***	22.94 ± 3.91	0.500	0.090
		Post-test	25.40 ± 4.58			23.17 ± 4.77
IADL
	Shopping Outdoors	Pre-test	1.84 ± 0.69	−3.50	0.002 ***	1.64 ± 0.58	3.06	0.045
		Post-test	2.13 ± 0.50			1.13 ± 0.56
	Going Out for Activities	Pre-test	1.81 ± 0.83	−2.68	0.012 **	1.64 ± 0.71	1.72	0.096
		Post-test	2.00 ± 0.82			1.61 ± 0.65
	food preparation	Pre-test	1.74 ± 0.68	2.40	0.223	1.58 ± 0.67	−2.96	0.106
		Post-test	1.90 ± 0.60			1.81 ± 0.60
	household maintenance	Pre-test	1.74 ± 0.84	3.59	0.101	1.59 ± 0.67	−2.96	0.066
		Post-test	2.19 ± 0.75			1.61 ± 0.70
	laundry	Pre-test	1.81 ± 0.59	2.40	0.123	1.55 ± 0.57	−3.23	0.073
		Post-test	1.87 ± 0.50			1.51 ± 0.48
	telephone use	Pre-test	1.81 ± 0.56	3.78	0.201	1.61 ± 0.56	−3.23	0.063
		Post-test	1.94 ± 0.51			1.67 ± 0.50
	medication administration	Pre-test	1.65 ± 0.49	−4.35	0.001 ***	1.61 ± 0.50	−4.65	0.100
		Post-test	2.03 ± 0.61			1.03 ± 0.55
	financial management	Pre-test	1.95 ± 0.51	3.50	0.092	1.36 ± 0.49	−1.14	0.200
		Post-test	1.84 ± 0.58			1.12 ± 0.56
Cognitive function
	Sense of orientation	Pre-test	7.71 ± 0.53	−1.53	0.117	8.23 ± 0.56	−2.78	0.101
		Post-test	7.84 ± 0.63			8.54 ± 0.72
	attention and calculation abilities	Pre-test	3.36 ± 0.88	−7.84	<0.001 ***	3.03 ± 0.75	−1.07	0.060
		Post-test	4.61 ± 0.92			2.94 ± 0.85
	memory	Pre-test	1.65 ± 0.55	−1.42	<0.001 ***	1.97 ± 0.61	−1.66	0.200
		Post-test	2.52 ± 0.51			1.48 ± 0.51
	language	Pre-test	2.10 ± 0.65	−5.30	<0.001 ***	2.39 ± 0.67	−1.53	0.067
		Post-test	2.58 ± 0.50			1.61 ± 0.50
	verbal comprehension	Pre-test	2.32 ± 0.60	−1.00	0.326	1.74 ± 0.63	−1.23	0.303
		Post-test	2.36 ± 0.61			1.00 ± 0.58
	constructional ability	Pre-test	0.97 ± 0.18	−1.00	0.325	0.74 ± 0.45	−3.23	0.603
		Post-test	1.00 ± 0.00			1.00 ± 0.00
Sleep quality
	Subjective sleep quality	Pre-test	1.32 ± 0.66	4.35	0.060	1.39 ± 0.61	3.50	0.072
		Post-test	1.94 ± 0.57			1.10 ± 0.60
	sleep onset latency (minutes)	Pre-test	1.32 ± 0.75	2.68	0.012 *	1.32 ± 0.65	3.23	0.103
		Post-test	1.13 ± 0.72			1.37 ± 0.57
	sleep duration (hours)	Pre-test	1.65 ± 0.61	4.06	0.003 ***	1.32 ± 0.65	4.06	0.300
		Post-test	1.29 ± 0.53			1.97 ± 0.61
	sleep efficiency (%)	Pre-test	1.39 ± 0.76	4.32	0.062	1.65 ± 0.61	5.91	0.600
		Post-test	1.07 ± 0.77			1.00 ± 0.58
	sleep disturbances (minutes)	Pre-test	1.16 ± 0.82	3.40	0.063	1.26 ± 0.58	1.79	0.083
		Post-test	1.00 ± 0.68			1.16 ± 0.52
	use of sleep medication	Pre-test	1.45 ± 0.93	1.41	0.169	1.23 ± 0.62	2.68	0.112
		Post-test	1.29 ± 0.59			1.03 ± 0.71
	daytime dysfunction (minutes)	Pre-test	0.87 ± 0.67	1.44	0.161	1.16 ± 0.68	2.99	0.076
		Post-test	0.81 ± 0.61			0.81 ± 0.54

* p < 0.05, ** p < 0.01, *** p < 0.001.

).

Meanwhile, based on gender, this study assessed pre- and post-test differences in physical function, cognitive function, and sleep quality for each group. The results indicated significant differences in physical function (t = 2.078, p < 0.05), cognitive function (t = 2.104, p < 0.05), and sleep quality (t = 2.093, p < 0.05) within the experimental group. However, no significant differences were observed based on gender in the control group (see

Table 3. Post-test differences between genders in physical function, cognitive function, and sleep quality.

Variables	Experimental Group (n = 29)						Control Group (n = 29)
	Physical Function		Cognitive Function		Sleep Quality		Physical Function		Cognitive Function		Sleep Quality
Gender	Mean ± SD	t-Value	Mean ± SD	t-Value	Mean ± SD	t-Value	Mean ± SD	t-Value	Mean ± SD	t-Value	Mean ± SD	t-Value
Male	21.56 ± 0.58	2.078 *	4.86 ± 0.56	2.104 *	2.35 ± 0.51	2.093 *	18.36 ± 0.45	1.264	3.57 ± 0.48	1.718	2.01 ± 0.11	1.546
Female	20.56 ± 0.67		6.86 ± 0.32		1.01 ± 0.11		19.06 ± 0.61		5.52 ± 0.98		1.85 ± 0.22

* p < 0.05.

).

3.3. Analysis of Demographic Characteristics, Physical Performance, Cognitive Function, and Sleep Quality Using the GEE

This study analyzed differences in physical and cognitive function and sleep quality between the experimental and control groups after 3 months of WBV training. The results revealed a significant increase in HGS in both the right hand (B = 0.203, 95% CI = 0.057–0.721, p < 0.005) and left hand (B = 0.130, 95% CI = 0.037–0.461, p < 0.005) in the experimental group compared with the control group. Furthermore, the experimental group exhibited significantly greater improvements in IADLs compared with the control group (B = 0.131, 95% CI = 0.035–0.489, p < 0.005).

In addition, the experimental group demonstrated a significant increase in cognitive function compared with the control group (B = 0.098, 95% CI = 0.01–0.87, p < 0.005) after 3 months of WBV training. Furthermore, regarding sleep quality, the experimental group exhibited significant improvements in sleep latency and sleep duration compared with the control group (B = 0.132, 95% CI = 0.03–0.5, p < 0.005) (

Table 4. Effectiveness of GEE analysis on physical function, cognitive function, and sleep quality between groups and over time after a 3-month intervention.

Group		Post-Test Mean (SE)	Pre-Test Mean (SE)	Mean Difference (SE)	p-Value	Group × Time	p-Value
Physical Function
Grip strength	(Right Hand)
	Experimental Group	26.62 (0.61)	24.84 (0.45)	1.78 (0.16)	<0.001 ***	0.203 (0.057–0.721)	<0.001 ***
	Control Group	22.94 (1.06)	25.24 (0.37)	−2.30 (0.69)	0.076
	(Left Hand)
	Experimental Group	25.58 (0.62)	23.42 (0.33)	1.16 (0.29)	0.022 *	0.130 (0.037–0.461)	<0.001 ***
	Control Group	22.67 (0.74)	25.41 (0.52)	−2.74 (0.22)	0.087
IADL
	Experimental Group	14.67 (0.18)	13.32 (0.17)	1.35 (0.01)	0.003 ***	0.131 (0.035–0.489)	0.005 **
	Control Group	12.90 (0.07)	12.68 (0.08)	0.22 (0.01)	0.079
Cognitive function
	Experimental Group	20.19 (0.78)	17.65 (0.04)	2.54 (0.74)	0.045	0.098 (0.010−0.870)	0.035 *
	Control Group	18.03 (0.07)	17.74 (0.14)	0.29 (0.07)	0.087
Sleep quality
	Experimental Group	7.52 (0.10)	9.16 (0.15)	−1.64 (0.04)	<0.001 ***	0.132 (0.03–0.05)	0.003 **
	Control Group	7.09 (0.13)	9.29 (0.12)	−0.21 (0.01)	0.089

* p < 0.05, ** p < 0.01, *** p < 0.001.

).

Meanwhile, this study assessed the intervention group compared to the control group in physical function, cognitive function, and sleep quality between the two groups (Figure 1).

4. Discussion

To the best of our knowledge, this study was the first study to investigate the effect of vertical stimulation training on physical and cognitive function and sleep quality in older individuals with dynapenia residing in long-term care facilities. The results revealed significant differences in HGS and IADLs in the experimental group after the intervention compared with before the intervention, whereas no such significant differences were observed in the control group. These findings are consistent with those of Young and Jung [22], who observed significant differences in grip strength and IADLs after WBV training compared with before such training among community-dwelling older adults. Rapid vibrations stimulate sensory receptors in the brain and motor receptors in the joints, muscles, and ligaments, activating brain reflexes and proprioceptive feedback loops. This mechanism enhances whole-body proprioception and motor function and promotes the strengthening of neuromuscular functions, thereby improving muscle reflexes and brain nerve circuit control. Furthermore, regarding cognitive function, the experimental group in the present study demonstrated significant improvements in attention, calculation ability, and memory after the intervention. Smolarek et al. [23] mentioned that vibration stimulated brain sensory receptors and spinal motor receptors in joints, muscles, and ligaments, activating brain reflexes and proprioceptive feedback loops, thereby enhancing whole-body proprioception and motor function and promoting the strengthening of neuromuscular functions, aiding in better muscle reflexes and brain nerve circuit control. Lin et al. [11] also pointed out WBV stimulated circulation and enhanced blood flow to the brain, which could improve oxygen and nutrient delivery, supporting cognitive processes and overall brain health. These findings are consistent with those of Santos et al. [24], who conducted an RCT to investigate the effect of cognitive training on cognitive and physical function in older adults. In that study, an experimental group underwent cognitive training three times a week for 12 weeks, whereas a control group received routine daily care without cognitive training. That study observed significant differences in memory and language abilities in the experimental group after the intervention compared with before the intervention, indicating improvements in cognitive and physical function in the analyzed older adults. Similarly, Smolarek et al. [23] conducted a study involving 21 older participants. In that study, an experimental group underwent 12 weeks of regular strength training, whereas a control group underwent no intervention exercises. Their findings revealed improvements in cognitive function in the experimental group, with significant differences observed between pretest and post-test; that result is consistent with that of the present study.

In the present study, the experimental group exhibited significant differences in sleep quality, sleep latency, sleep duration, and sleep efficiency between pretest and post-test, whereas no such significant differences in sleep parameters were observed in the control group. Lin et al. [11] mentioned that WBV could stimulate blood flow and enhance cardiovascular function, which may promote better tissue oxygenation and metabolic waste removal, contributing to improved sleep. Wei et al. [25] also pointed out that vibrations from WBV could induce muscle relaxation and reduce muscle tension, which may facilitate a more restful sleep by alleviating physical discomfort and stress. These findings are consistent with those of Palop-Montoro et al. [26], who conducted a study involving 52 individuals aged 65 years and older, randomly assigning these individuals to an experimental group and a control group. The experimental group underwent four sessions of WBV training per week for 12 weeks, which led to considerable improvements in sleep quality and duration. Lin et al. [11] investigated the effects of WBV training on sleep quality in older residents of care facilities. Their findings demonstrated significant differences in sleep quality between pretest and post-test in the experimental group, indicating that the WBV training had effectively improved sleep quality. Meanwhile, this study found that gender had significant differences in physical function, cognitive function, and sleep quality in the experimental group. However, there were no significant differences in the control group. Yang et al. [27] mentioned that gender differences in health outcomes can be attributed to biological, social, and behavioral factors. In the experimental group, the significant gender differences indicate that the intervention may have interacted with these gender-specific factors. Conversely, the lack of significant differences in the control group suggests that, without the intervention’s influence, inherent gender disparities were less pronounced. Overall, these findings highlight the importance of considering gender-specific factors in the design and evaluation of health interventions. Future research should further explore these aspects to better understand and address gender-related disparities in health outcomes.

The present study performed GEE analysis to compare differences in physical function between the experimental and control groups, particularly in terms of grip strength and IADLs. The results revealed that after 3 months of WBV training, compared with the control group, the experimental group exhibited superior performance in grip strength and various IADL tasks, including shopping, outdoor activities, food preparation, housekeeping, doing laundry, phone usage, medication management, and handling finances. These findings are consistent with those of Pothier et al. [28], who observed significant improvements in grip strength and physical function in 137 community-dwelling individuals aged 60 years and older after an intervention. In addition, Tseng et al. [29] administered three weekly sessions of WBV training, each lasting 5 min, at a fixed amplitude of 4 mm for 3 months. They observed improvements in muscle strength, flexibility, and balance among older individuals after the intervention compared with before the intervention, which was consistent with the findings of the current study. Similarly, Coelho-Oliveira et al. [30] indicated that WBV training could enhance physical function outcomes in community-dwelling older adults. Specifically, improvements were observed in physical function and neuromuscular flexibility, which, in turn, contributed to better metabolic health and increased physical activity. These findings are consistent with those of the present study. Furthermore, upon comparing cognitive function between the experimental and control groups through GEE analysis, the present study found that after the intervention, the experimental group demonstrated significantly greater improvements in attention, calculation ability, and memory compared with the control group. This outcome suggests that WBV training can effectively enhance cognitive function in older individuals with dynapenia. This finding is consistent with that of Pellegrini-Laplagne et al. [31], who examined 35 healthy older individuals. That study’s experimental group underwent 24 weeks of WBV training twice a week for 30 min per session, whereas its control group received routine daily care. Their results revealed that WBV training was more effective than any other single training method alone in improving cognitive function.

The present study compared differences in sleep quality between the experimental and control groups by performing GEE analysis and determined that after WBV training, the experimental group demonstrated significant improvements in both subjective sleep quality and objective sleep parameters—including sleep latency, sleep duration, sleep efficiency, sleep disturbances, sleep medication usage, and daytime dysfunction—compared with the control group. This finding is consistent with that of Azeredo et al. [32], who conducted an RCT involving 19 participants who underwent 6 weeks of WBV training once a week. They observed that their experimental group experienced more considerable improvements in sleep quality compared with their control group. Similarly, Wei et al. [25] examined healthy older individuals who underwent 3 months of WBV training involving the use of horizontal vibration stimulation at a frequency of 26 Hz and an amplitude of 5–8 mm. The participants performed weight-bearing exercises on a vibration platform three times a week, with each set lasting between 45 and 80 s. Their results indicated that the experimental group experienced greater improvements in physical activity function compared with the control group, which was consistent with the findings of the present study.

Based on the results of this study, 12 weeks of regular WBV training demonstrated positive effects on physical function, cognitive function, and sleep quality. However, the potential long-term effects of WBV are worth noting. Coelho-Oliveira et al. [30] conducted a systematic review and meta-analysis, finding that long-term WBV training showed promising results in enhancing physical function, with sustained improvements in muscle strength, balance, and overall performance. The stimulation provided by WBV may lead to increased neuromuscular adaptation, potentially reducing the risk of falls and improving mobility. Additionally, Pellegrini-Laplagne et al. [31] suggested that the long-term effects of WBV could arise from its ability to stimulate sensory and motor pathways essential for cognitive processing. By enhancing proprioceptive feedback and brain reflexes, WBV may contribute to better cognitive performance and potentially delay cognitive decline in older adults. Furthermore, Palop-Montoro et al. [26] and Wei et al. [25] emphasized WBV’s role in improving both subjective and objective sleep parameters among older individuals. Lin et al. [11] highlighted that the potential long-term effects of WBV on sleep quality could contribute to overall well-being and recovery, possibly through the regulation of circadian rhythms and reduction in sleep disturbances. Therefore, future research should focus on the long-term effects of WBV and explore the optimal duration and frequency of WBV sessions.

Limitations

The present study had several limitations that should be addressed. First, this study excluded older individuals with severe medical conditions or those unable to stand for 5–10 min; this feature may have affected the external validity and limited the generalizability of the findings to all older residents with dynapenia residing in long-term care facilities. In addition, the intervention period was short: only 3 months; accordingly, future studies should consider extending both the duration and frequency of the present intervention to assess the long-term efficacy of WBV training. Nevertheless, despite these limitations, to the best of our knowledge, this study was the first study to investigate the effects of WBV training on physical and cognitive function and sleep quality in older residents with dynapenia in institutional care settings. Therefore, the findings of this study hold significant clinical relevance and thus warrant attention from healthcare professionals regarding their consideration for application in clinical practice.

5. Conclusions

In this study, the experimental group exhibited significant improvements in physical and cognitive function and sleep quality after 3 months of WBV training compared with the control group. WBV training led to significant improvements in all the assessed areas, indicating its potential as an effective intervention for improving health outcomes in older adults with dynapenia.