Comparison of body composition between patients admitted to convalescent rehabilitation and long-term care wards

Abstract

[Purpose] This study aimed to assess the differences in body composition, including phase angle, extracellular water-to-total body water ratio, and skeletal muscle index, between patients in convalescent rehabilitation and long-term care wards. Understanding these differences is essential for tailoring patient care and rehabilitation strategies given that body composition plays a key role in recovery and functional outcomes. [Participants and Methods] In total, 160 patients (73 males and 87 females) in convalescent rehabilitation wards and 26 patients (9 males and 17 females) in long-term care wards participated in this study. Body composition, height, and weight were measured using an InBody S10 device, which allows measurements in both seated and lying positions. [Results] Significant differences in phase angle, extracellular water-to-total body water ratio, and skeletal muscle index were observed between patients in the convalescent rehabilitation and long-term care wards, with larger differences noted among female participants. Specifically, the skeletal muscle index was lower in the patients from long-term care wards, suggesting reduced muscle mass in this group. [Conclusion] Body composition differed between patients in the convalescent rehabilitation and long-term care wards. These findings highlight the need for personalized care and rehabilitation based on body composition to improve patient outcomes.

INTRODUCTION

The Japanese healthcare system includes convalescent rehabilitation wards where patients who have completed acute care receive intensive rehabilitation to restore their function and return to daily life. Patients in these wards often transition back to the community through rehabilitation^{1, 2)}. In contrast, long-term care wards primarily serve elderly patients with chronic diseases³⁾, who require continuous nursing care and are less likely to return to their communities. Body composition, including phase angle (PhA), extracellular water-to-total body water ratio (ECW/TBW), and skeletal muscle index (SMI), is known to influence patient outcomes, rehabilitation success, and quality of care in clinical settings. PhA reflects cellular health and is significantly related to the length of hospital stay and mortality⁴⁾. ECW/TBW indicates body water balance and can indicate edema caused by acute inflammation, renal disease, and other medical conditions⁵⁾. SMI indicates the amount of skeletal muscle mass in the limbs and is a factor associated with mortality in frail elderly patients in convalescent wards and in those in need of nursing care⁶⁾. However, there is limited research directly comparing body composition metrics between these two ward types, and how these differences might inform care strategies remains unclear^7,8,9).

This study aimed to fill this gap by measuring body composition in patients from convalescent rehabilitation and long-term care wards to identify key differences that could improve patient management and care approaches.

PARTICIPANTS AND METHODS

This was a single-center, cross-sectional study conducted at the International University of Health and Welfare, Shioya Hospital. A total of 186 patients (82 males, age 76.1 ± 10.8 years, height 159.3 ± 8.3 cm, weight 52.9 ± 10.0 kg; 104 females, age 83.3 ± 9.6 years, height 143.6 ± 6.8 cm, weight 42.8 ± 7.6 kg; mean ± standard deviation) were admitted to convalescent rehabilitation wards of the International University of Health and Welfare, Shioya Hospital, from August 2021 to January 2024. The participants included 160 patients (73 males, age 72.7 ± 12.8 years, height 164.0 ± 7.5 cm, weight 58.0 ± 9.8 kg; 87 females, age 81.0 ± 9.5 years, height 147.8 ± 7.2 cm, weight 47.6 ± 9.4 kg) in convalescent rehabilitation wards and 26 patients (9 males, age 79.4 ± 8.8 years, height 154.6 ± 9.2 cm, weight 47.8 ± 10.2 kg; 17 females, age 85.7 ± 9.8 years, height 139.5 ± 6.3 cm, weight 38.0 ± 5.9 kg) in long-term care wards; all patients provided consent.

Patients admitted to the convalescent rehabilitation wards are those who have completed acute care and are in need of rehabilitation to restore function, and include neurosurgery, neurology, and orthopedics. The goal of care is discharge home. Inpatients in the long-term care wards are patients with chronic diseases or disabilities that are difficult to cure or significantly restore function and require long-term support. The goal of care is to maintain residual capacity and prevent contractures.

The measurements included height, weight, and body composition. Height was measured using an ultrasonic height meter (InLab, InBody Co., Tokyo, Japan), and those who could not hold a standing position were measured using a measuring tape in the supine position. Body weight was measured prior to body composition assessment, and body mass index (BMI) was calculated based on weight and height. Body composition was measured using a multifrequency bioimpedance device (InBody S10, InBody Co.), which accommodates measurements while participants are supine or seated, beneficial for individuals with severe dysfunction or those who are bedridden^10,11,12). The participants were all inpatients in the hospital ward.

The exclusion criteria included individuals lacking permission from their attending physician, those with implanted electronic medical devices such as pacemakers, and those on life-support devices such as biometric monitors. In accordance with the Declaration of Helsinki, this study was conducted after explaining the study to the participants or their families. This study was reviewed and approved by the Research Ethics Review Committee of the International University of Health and Welfare (approval number: 23-Io-10).

For statistical analysis, the Mann–Whitney U test was employed to compare height, weight, BMI, and body composition (PhA, ECW/TBW, and SMI) among patients in different wards, as the data did not meet the normality assumption. The effect size, r, was calculated to indicate the size of the difference in means between the groups. The effect size is a standardized measure of the strength of the relationship between variables that does not vary with sample size. The effect sizes were interpreted as r=0.10 to 0.29: small, 0.30 to 0.49: medium, and 0.50<: large¹³⁾. All statistical analyses were performed using SPSS Statistics version 29 (IBM), and a p-value <0.05 was considered statistically significant.

RESULTS

Male participants in the convalescent rehabilitation wards had a BMI of 21.5 ± 2.9 kg/m² and a PhA of 4.4 ± 1.0°, an ECW/TBW of 0.401 ± 0.012, and an SMI of 6.6 ± 1.0 kg/m², while those in the long-term care wards had a BMI of 20.0 ± 4.0 kg/m², a PhA of 3.1 ± 1.1°, an ECW/TBW of 0.417 ± 0.012, and an SMI of 4.5 ± 1.4 kg/m². Female participants in the convalescent rehabilitation wards had a BMI of 21.8 ± 4.1 kg/m², a PhA of 3.7 ± 0.8°, an ECW/TBW of 0.408 ± 0.016, and an SMI of 5.3 ± 1.1 kg/m², while those in long-term care wards had a BMI of 19.6 ± 3.0 kg/m², a PhA of 2.6 ± 0.8°, an ECW/TBW of 0.420 ± 0.017, and an SMI of 3.1 ± 0.7 kg/m² (Table 1). Significant differences were observed in PhA, ECW/TBW, and SMI between male and female participants. The effect sizes were more prominent in the SMI group (r=0.55 for males, r=0.89 for females) (Table 2).

Table 1. Patient characteristics and measurement results.

	Total, n=186		Males, n=82		Females, n=104
	Convalescent rehabilitation wards	Long-term care wards	Convalescent rehabilitation wards	Long-term care wards	Convalescent rehabilitation wards	Long-term care wards
	n=160	n=26	n=73	n=9	n=87	n=17
Characteristics
Age (years)	77.2 ± 11.8	83.5 ± 9.8	72.7 ± 12.8	79.4 ± 8.8	81.0 ± 9.5	85.7 ± 9.8
Height (cm)	155.2 ± 10.9*	144.7 ± 10.3*	164.0 ± 7.5*	154.6 ± 9.2*	147.8 ± 7.2*	139.5 ± 6.3*
Weight (kg)	52.4 ± 10.9*	41.4 ± 8.8*	58.0 ± 9.8	47.8 ± 10.2	47.6 ± 9.4*	38.0 ± 5.9*
BMI (kg/m2)	21.7 ± 3.6	19.7 ± 3.3	21.5 ± 2.9	20.0 ± 4.0	21.8 ± 4.1	19.6 ± 3.0
Body composition
PhA (°)	4.0 ± 0.9*	2.8 ± 0.9*	4.4 ± 1.0*	3.1 ± 1.1*	3.7 ± 0.8*	2.6 ± 0.8*
ECW/TBW	0.405 ± 0.015*	0.419 ± 0.015*	0.401 ± 0.012*	0.417 ± 0.012*	0.408 ± 0.016*	0.420 ± 0.017*
SMI (kg/m2)	5.9 ± 1.2*	3.6 ± 1.2*	6.6 ± 1.0*	4.5 ± 1.4*	5.3 ± 1.1*	3.1 ± 0.7*

Mean ± standard deviation (SD), BMI: body mass index; PhA: phase angle; ECW/TBW: extracellular water-to-total body water ratio; SMI: skeletal muscle index (limb muscle mass/height/height/height/1,000), paired t-test *p<0.05.

Table 2. Effect size indicating the difference in means between the groups.

	Total, n=186	Males, n=82	Females, n=104
Characteristics
Age (years)	0.40	0.17	0.36
Height (cm)	0.32	0.36	0.40
Weight (kg)	0.67	0.67	0.68
BMI (kg/m2)	0.42	0.34	0.43
Body composition
PhA (°)	0.43	0.40	0.48
ECW/TBW	0.60	0.39	0.48
SMI (kg/m2)	0.85	0.55	0.89

Effect size r=0.10–0.29: small, 0.30–0.49: medium, 0.50<: large.

BMI: body mass index; PhA: phase angle; ECW/TBW: extracellular water-to-total body water ratio; SMI: skeletal muscle index.

DISCUSSION

The results of this study revealed significant differences in body composition between male and female patients admitted to convalescent rehabilitation wards and long-term care wards. Convalescent rehabilitation wards provide enhanced social support and assistance that may positively influence body composition and contribute to long-term health recovery.

In this study, SMI differed significantly between the recovery and long-term care units for both men and women, with notably larger effects observed in women. Previous research has indicated that decreased SMI is associated with diminished activities of daily living (ADL) and progressive loss of muscle mass and strength, which adversely impact functional prognosis^{14, 15)}. The SMI reflects skeletal muscle mass and serves as a direct indicator of the effects of exercise and nutrition. Therefore, targeted rehabilitation and adequate protein intake may promote muscle fiber hypertrophy and remodeling.

PhA was significantly lower in patients in the long-term care unit compared to those in the rehabilitation unit, particularly among women. PhA is a widely accepted indicator of cell membrane integrity and intra- and extracellular water balance. A low PhA often suggests malnutrition, chronic inflammation, and compromised cellular integrity¹⁶⁾, which can adversely affect the independence of these patients and serve as survival predictors.

ECW/TBW, another critical indicator of body fluid distribution, was also examined^{17, 18)}. The findings suggest that edema may be more prevalent in long-term care patients due to restricted mobility and muscle weakness, which can lead to fluid imbalances.

Based on the above, in terms of nutritional management of inpatients in long-term care wards, it is necessary to provide meals in a form that is easy to consume even for patients who tend to have a low appetite (paste meals, jelly meals) and to utilize beverages and smoothie-type protein supplement foods. In addition, because postmenopausal women in particular tend to have decreased muscle mass, exercise should be set up that can be performed at the bedside according to the patient’s physical function and fitness level.

Patients admitted to convalescent rehabilitation wards come in with a range of energy levels, from high to low energy expenditure, so nutritional guidance should be provided to maintain daytime activity during hospitalization and to reflect this at home.

However, this study has some limitations. Certain data were not measured during hospitalization, including dietary intake and blood data such as D-dimer. In addition, although patients were classified by department, detailed onset and history of disease were not considered, so the impact of timing of measurements must be considered. Individual differences in nutritional status due to illness and disease progression as well as environment at discharge must be considered. Future interventions aimed at improving nutritional status and overall health are needed.

In conclusion, our results indicate that differences in body composition among ward inpatients may correlate with their nutritional status. Changes in PhA, ECW/TBW, and SMI can serve as valuable indicators for assessing nutritional status and fluid balance. Personalized treatment strategies based on these indicators could significantly enhance patient outcomes. The differences in body composition observed in this study highlight the importance of tailored rehabilitation strategies that consider the unique needs of patients in various care settings.

Funding

This study was supported by JSPS KAKENHI, Grant Numbers 21K10581 and 24K23756.

Conflicts of interest

The authors have no competing interests to declare that are relevant to the content of this article.