According to the age-specific demographic data released by the National Statistical Office in South Korea, the proportion of older adults aged 65 or older accounted for 14.3% of the total population by 2018; this proportion is projected to increase every year, with an estimate of reaching 15.7% in 2020, 25.0% by 2030, and 34.4% by 2040 [1]. Additionally, it was reported that most older adults have chronic diseases, 43.3% of them have limitations in activities of daily living, and at least 8% of older adults are currently in need of nursing care owing to dementia [2]. In modern society, there is an increasing demand for facilities and nursing care services to support older adults with chronic diseases and their families, because family functions for supporting older adults are weakened owing to a decrease in the number of family members and women’s active entry into society [3]. As compared to before the implementation of the long-term care insurance system, the number of long-term care service institutions and care workers has increased two to three times recently, and is expected to continue to increase [4]. Nursing homes are emerging as increasingly important palliative care providers and employers in modern society.

Nursing home workers usually consume a significant amount of energy because of repetitive and fast tasks, such as taking care of patients’ eating, dressing, bathing and toilet and moving them from bed to chair [5]. In particular, since patients in nursing homes rely heavily on nursing care for almost all their activities of daily living, workers caring for nursing home patients may particularly be at risk of developing musculoskeletal disorders owing to the nature of their job [6, 7]. As a result, workers in nursing homes complain of musculoskeletal symptoms and fatigue, which negatively affect job stress [8]. Some studies have reported that home care and nursing home workers had more work-related injuries due to tasks than other occupations, and higher levels of care dependency in patients were associated with a higher incidence of musculoskeletal disorders in caregiving workers [9, 10]. A study involving hospital workers reported that the prevalence of musculoskeletal symptoms, back pain, neck and shoulder pain, and knee pain among nurses and patient care assistants in the last three months was 74%, 53%, 42%, and 37%, respectively [11]. In a previous study on musculoskeletal symptoms of caregivers, 31.8% of caregivers showed musculoskeletal symptoms, of which 45.2% reported lower extremity pain [8]. Physical exposure causing musculoskeletal pain includes patient transport work requiring patient handling out of bed and tasks using strong physical force [11, 12].

Interventions such as stretching, exercise, cold and heat therapy, and massage for muscle atrophy and weakness are effective in relieving pain and increasing flexibility [13, 14, 15]. Among them, contrast therapy, which includes alternating heat and cold therapy, is effective in reducing musculoskeletal edema and pain and is an effective intervention to increase muscle elasticity [16]. In general, local cold therapy (or cryotherapy) is used as an intervention to reduce skin and tissue temperature to induce vasoconstriction, reduce blood flow, and prevent tissue fluid movement, thereby reducing edema and slowing nerve transmission speed, and finally controlling pain [17]. Heat therapy is used as an effective intervention to relieve joint stiffness by increasing connective tissue elasticity and promoting inflammatory processes and wound healing [18]. Previous studies reported that pain and related symptoms were significantly reduced by the contrast applications of cold and warm therapy as compared to the single application of cold or warm therapy in osteoarthritis patients [19]; additionally, muscle soreness and fatigue significantly reduced as compared to the control group when athletes were subjected to contrast therapy using water after training [20]. However, contrast bath therapy, which is often used as a contrast therapy, has limitations in its application because it requires a large amount of water, mobility and usable locations, and maintenance of a constant temperature.

Therefore, this study aimed to investigate the effects of contrast therapy using a flexible Thermoelectric Device (TED)—that can maintain a constant temperature and change the temperature within a short period of time—on lower extremity edema, pain, muscle fatigue, and stress in nursing home workers.

This study aimed to investigate the effects of contrast therapy using flexible TED, which is capable of heat/cold temperature control, on lower extremity pain, edema, muscle fatigue, and stress in care workers who belong to an occupational group with a high musculoskeletal burden. The results showed that contrast therapy using flexible TED had positive effects on care workers and that there was a statistically significant difference in lower extremity pain, edema, and stress index between the groups. The results of this study are as follows:

Although the mechanism by which alternating the use of heat and cold treatments affects the recovery of damaged muscle has not yet been clearly identified, the following three points can be considered. First, heat therapy, which forms an important part of contrast therapy, might enhance vasodilation to increase oxygenation and metabolite excretion [24]. This study indicated that such a phenomenon occurred to some extent because the contrast therapy using a 40℃ TED was applied six times for 4 minutes per treatment session for a total of 24 minutes. In addition, heat therapy might increase the immune response to muscle damage, similar to symptoms occurring during fever, and this response might accelerate muscle recovery [25]. In fact, Viitasalo et al. reported that when applying 37℃ underwater water jet massage to athletes after training, muscle function maintenance was improved, and Creatine Kinase (CK) and myoglobin levels were increased in those receiving warm water therapy compared to the control group [26]. The authors suggested that warm water therapy might increase the release of proteins from the muscle into the blood, and that the increased protein release might reduce the percentage of muscle components degraded in the extracellular matrix [27]. Second, cold therapy with contrast may reduce nerve conduction velocity and decrease nerve transmission [28]. In addition, Gregson suggested that blood flow to muscles may be lowered after 8~20℃ cold pack application, and stated that this may be because the activation of heat receptors may result in changes in sympathetic activity, thereby decreasing arterial flow [29]. Therefore, the physiological effects of cold therapy may be partially mediated through a decrease in microvascular blood flow around the injured site, which in turn can reduce edema and inflammation induction. Finally, the alternating use of cold and heat therapy can result in drastic changes in muscle perfusion owing to a combination of cold / heat effects, which is called the pumping effect [30]. It has been reported that the pumping effect might cause changes in muscle perfusion through vasodilation and vasoconstriction, thereby weakening the immune response and reducing muscle cell damage. In this study, no vasodilation or constriction was observed; however, muscle pain and edema were significantly reduced after contrast therapy. Vaile et al. reported in a study examining 15℃ / 38℃ contrast bath therapy (15℃ cold water therapy, and 38℃ warm water therapy) that the 15℃ cold water therapy was effective in reducing physiological and functional deficits related to muscle pain, including muscle recovery and edema reduction, and 38℃ warm water therapy was effective for muscle recovery, but had no effect on other recovery as compared to the control group [31]. It can be concluded that contrast therapy is effective in helping muscle recovery and reducing pain, and edema. Comparative studies with cold therapy that show similar results are needed to further clarify the effects of contrast therapy.

Stress refers to a state of physical, physiological, and psychological tension that an individual experiences in difficult situations [32]. Excessive stress can have negative effects on mental and physical health, cause deterioration of work quality, and should be properly relieved [32]. This study found a significant difference in the stress index, which measured the autonomic nervous system index based on heart rate variability, before and after the experiment, between the two groups. In addition, perceived stress showed no statistically significant difference but decreased by 4.47 points in the experimental group and 2.83 points in the control group, showing more reduction effects in the experimental group. As studies regarding the effects of contrast therapy on stress could not be identified, a direct comparison between this study and other studies was not feasible. However, it was reported that the use of 40℃ foot bath therapy 4 days per week for 3 weeks in operating room nurses was helpful in relieving stress [33], and stress has been reported to have a significantly positive correlation with musculoskeletal disorders such as back pain [34]. Hence, it is thought that the contrast therapy used in this study might alleviate lower extremity discomfort and thus reducing stress.

Taken together, the results of this study are significant in confirming that contrast therapy using a flexible TED has similar effects to contrast bath therapy using water temperature. In addition, a study by Kim reported that both contrast bath therapy using 38~40℃ hot water and 12~14℃ cold water, and contrast therapy using a 38~40℃ infrared heating device and a 12~14℃ refrigeration device was effective in enhancing muscle recovery, confirming that both wet heat therapy using immersion bath and dry heat therapy using infrared rays and a refrigeration device can help muscle recovery [16]. Therefore, since contrast therapy using flexible TED can minimize individuals’ movement without moving themselves while alternating cold/heat therapy and maintain a constant temperature, it is considered an effective intervention method.

This study was conducted using a randomized controlled pretest-posttest experimental design to understand the effect of contrast therapy using flexible TED on the musculoskeletal system and stress of workers in nursing institutions. In order to confirm the effectiveness of contrast therapy using flexible TED, 40℃ heat therapy and 12℃ cold therapy were applied to the study participants six times for 4 minutes and 1 minute, respectively. The results showed that contrast therapy using flexible TED had a positive effect on leg edema, pain, muscle fatigue, and stress. Therefore, we believe that the results of this study provide positive scientific evidence for the application of contrast therapy using flexible TED and that contrast therapy using flexible TED can be used as an intervention to alleviate musculoskeletal problems in healthcare workers. However, this study has a risk of performance bias because the researcher was not blinded by random sequence generation and intervention, and there is a limit to generalization as a study was conducted at a single nursing institution.

Based on the results of this study, I suggest the following. First, this study was conducted at a nursing institution in one location, and there are limitations in generalization; therefore, further studies are needed. Second, in this study, the effect before and after therapy was verified by applying six on-therapy sessions for 4 minutes and cold therapy for 1 minute; however, for future studies, I recommend comparing and verifying the effect on time flow. Third, because the effects of contrast therapy, heat therapy, and cold therapy may vary depending on the use of flexible TED, a comparative study of these effects is suggested.