1. Introduction
The incidence of stroke is increasing with the increasing average life span and aging. Despite the advances in acute management, stroke remains a major cause of disability worldwide [
1]. Many stroke survivors report long-term disability and reduced quality of life [
2,
3]. The effects of stroke may include sensory, motor, and cognitive impairment as well as a reduced ability to perform self-care and participate in social and community activities [
4,
5].
Motor impairment after a stroke typically affects the control of arm and leg movement on one side of the body [
6,
7]. Stroke patients have disabilities that result from paralysis, and most complain of difficulties in walking [
8]. A common feature of walking after a stroke includes decreased gait velocity [
9]. Stroke patients also have an increased body sway because of their decreased balance function and distorted standing posture [
10,
11]. Balance problems are also believed to be common after stroke, and they have been implicated in the poor recovery of the activities of daily living (ADL) and mobility and the increased risk of falls [
12]. In addition, complex motor activities have been investigated such as reaching while standing and showed how stroke subjects had more endpoint trajectory variability than healthy [
13]. Much of the focus of stroke rehabilitation, in particular the work of physical therapists, is focused on the recovery of physical independence and functional ability during ADL; the ultimate goal of therapy is to improve the function of walking and recovery of balance and movement [
7]. Researchers have attempted to achieve the goal by finding the most effective rehabilitation for recovery in stroke patients [
1,
14]. Various novel stroke rehabilitation techniques for motor recovery have been developed based on basic science and clinical studies [
1]. A recent study about neurophysiological mechanisms for enhancing stroke recovery have shown that pharmacological interventions might promote neural plasticity and could potentially enhance the effectiveness of post-stroke motor therapies. In addition, therapies that directly stimulate the PNS or CNS may enhance neuroplasticity during post-stroke rehabilitation, and these might help patients with stroke overcome their motor impairments [
15]. In the post-acute stage (<3 months after stroke), the focus shifts to neurorehabilitation that may include exercise combined with technology such as robot-assisted training [
16] or neuromuscular electrical stimulation for UL rehabilitation [
17], which has been shown to play a key role in functional recovery. Clinical trials aiming at enhancing training-based neuroplasticity have incorporated different principles of motor learning [
18] and treatment interventions [
19]. On the other hand, the effectiveness of interventions among patients with stroke varies widely because of the heterogeneous mechanisms underlying motor recovery [
1]. Currently, no single standard intervention has been identified that is effective for recovering function after stroke [
20].
Previous studies suggested that stroke rehabilitation programs should include meaningful, repetitive, intensive, and task-specific movement training in an enriched environment to promote neural plasticity and functional recovery [
18,
21]. In addition, most recovery is believed to be made in the first stages after stroke [
5,
22]. Hence, the physical and psychological condition of the patient in the acute stage is essential. On the other hand, even if the early period of stroke rehabilitation is critical to their recovery, physical therapists cannot enforce meaningful, repetitive, intensive, and task-specific training on the patients. Therefore, the patients themselves have to actively participate in the rehabilitation for their recovery after stroke, even if the training is difficult. Active participation in rehabilitation could be related to self-control. Self-control is conceptualized as the extent of a person’s self-perception of having control over events and ongoing situations and reflects the perception of an ability to manage them [
23,
24]. Furthermore, feeling control is important for psychological adjustment, which has been the strongest predictor of a person’s ability to carry out behaviors for achieving the desired goal by taking action [
23,
25]. Several studies investigated individual differences in self-control, which are known as self-regulation in psychology, and reported that high levels of self-control are linked to positive outcomes [
23,
26]. In addition, self-control, a psychological factor, should not be overlooked in the rehabilitation of stroke survivors [
23].
Self-control is currently one of the most popular topics of psychological research. Its popularity is driven by the fundamental role of behavioral self-regulation in maintaining appropriate functioning in day-to-day life [
27]. The definition of self-control is usually straightforward and is typically associated with regulating emotions, desires, and behavior [
28]. Nęcka et al. introduced five behavioral components of self-control: (1) goal maintenance, or the ability to consider one’s intentions and long-term plans; (2) proactive control, defined as the ability to develop plans, prioritize goals, analyze consequences, and predict obstacles; (3) initiative and persistence, understood as the ability to set goals and take actions to follow one’s decisions without unnecessary delays; (4) switching and flexibility, or the ability to adjust to changing circumstances and manage attention during the performance of appropriate actions; (5) inhibition and adjournment, defined as the ability to inhibit emotional reactions and refrain from immediate, impulsive behavior [
27]. These behavioral components of self-control could be important when stroke patients participate in rehabilitation. Tangney et al. reported that self-control is involved in managing stress, focusing attention on specific tasks, modifying their responses according to their needs, and planning and performing the activities required to achieve long-term goals [
29]. Numerous research findings showed that high self-control is related to better outcomes in various areas such as physical health, substance dependence, higher scholastic performance, coping better with frustration and stress, personal finances, and criminal offending outcomes [
30,
31,
32]. In addition, a previous study suggested using the self-control level to predict people’s achievement [
33]. Physical goals, such as increasing muscle strength, balance, gait ability, and independence of ADL are also achievements that stroke patients want to accomplish. Self-control is a complex phenomenon that involves many psychological functions and has a strong impact on everyday performance [
27]. In South Korea, stroke patients who are hospitalized receive treatment at least five days a week. The long-term rehabilitation is a difficult task, particularly in patients with neurological problems, such as stroke. Self-control, which includes goal maintenance, proactive control, initiative and persistence, switching and flexibility, and inhibition and adjournment, will be necessary for rehabilitation and recovery outcomes.
Positive emotion is also recognized as an essential factor in people’s achievement [
33]. Positive emotion is measured by the positive and negative experiences in daily life [
34]. Salovey et al. reported that positive emotions and healthy outcomes might be linked through multiple pathways [
35]. Positive emotional states may promote healthy perceptions, beliefs, and physical well-being. Recently, many studies focused on the physical function and emotional problems in stroke patients [
36,
37,
38,
39]. This is because psychological factors greatly influence the physical and functional activities [
40]. Previous studies suggested that positive emotions significantly affect functional capacity [
41,
42]. A higher positive emotion was significantly associated with higher motor, cognition, and ADL ability in stroke patients and with the gains in functional status post-stroke [
43]. A previous study organized numerous research data (cross-sectional, longitudinal, and experimental studies) to identify the effects of positive emotion [
44]. In the review article, numerous studies showed that people who experience frequent positive emotions achieved more in diverse domains than those who did not. The evidence suggests that positive emotion may cause many desirable characteristics, resources, and successes [
44]. Positive people appear to be relatively more likely to seek approach goals. The interaction of cognitive judgments about the desire for a change with the propensity for a positive emotion is a ripe area of inquiry for the future [
44]. These people can have goals and experience positive emotion due to the progress they make toward those goals. Positive people also perform well in many areas that require motivation and persistence. At the same time, specific dissatisfaction can also motivate happy people to work for a change and pursue new directions [
44]. Several theories have proposed that high positive emotion is related to increased recovery following an acute medical event [
45,
46,
47]. Other studies found that negative emotions decreased muscle strength and could adversely affect the physical function [
36,
40,
48,
49]. In addition, many studies reported that negative emotions, such as depression, anxiety, emotionalism, and post-traumatic stress disorder interfere with recovery and cause stroke patients to lack the motivation to participate in rehabilitation, leading to decreased participation in ADL [
20,
50,
51].
Many researchers have examined the important factors related to physical ability and functional recovery in stroke patients. Recently, the psychological effects have been debated widely in stroke rehabilitation. Previous studies did not consider the stroke patient’s self-control and positive and negative emotion as important factors of physical ability and functional recovery. Moreover, most stroke rehabilitation still focuses on physical problems without addressing the psychological effects. This study examined whether self-control and emotions could influence physical ability and functional recovery after a stroke. We expect that there is a positive correlation between self-control level and function recovery in stroke patients.
3. Results
The general characteristics of the subjects are shown in the
Table 1.
Changes in physical variables in stroke patients during eight weeks are shown in
Table 2 and
Figure 2. The velocity, cadence, and affected side single support increased significantly for eight weeks (
p < 0.05). The COP path length and COP sway velocity decreased significantly for eight weeks. Weight bearing on the affected side increased significantly (
p < 0.05). The knee extensor strength increased significantly for eight weeks (
p < 0.05). The FIM score increased significantly for eight weeks (
p < 0.05). There was no significant change in self-control, positive emotion, and negative emotion for eight weeks (
p > 0.05) (
Table 3) (
Figure 3).
No significant correlation was observed between the self-control and physical variables at the baseline, four weeks, and eight weeks (
p > 0.05) (
Table 4).
No significant correlation was observed between the positive emotion and velocity, cadence, affected side single support, COP path length, weight-bearing on the affected side, knee extensor strength, and Functional Independence Measure at the baseline, four weeks, and eight weeks (
p > 0.05). A significant correlation was observed between positive emotion and COP sway velocity at the eight weeks (
p < 0.05) (
Table 5).
Significant correlation was observed between the negative emotion and velocity, cadence, affected side single support, COP path length, COP sway velocity, knee extensor strength, and Functional Independence Measure (
p < 0.05) (
Table 6).
Significant correlation was observed between the self-control at the baseline and changes in velocity, cadence, COP sway velocity, weight bearing on the affected side, and knee extension muscle strength during four weeks (
p < 0.05). Significant correlation was observed between the self-control at the baseline and changes in velocity, cadence, and COP sway velocity during eight weeks (
p < 0.05) (
Figure 4). No significant correlation was observed between the positive emotion at the baseline and changes in physical variables during four and eight weeks (
p > 0.05) (
Figure 4). No significant correlation was observed between the negative emotion at the baseline and changes in physical variables during four and eight weeks (
p > 0.05) (
Figure 4).
4. Discussion
This study is the first to determine that self-control and emotion could influence the physical ability and functional recovery in acute stroke patients. The results showed that the self-control level affects the functional recovery and improvement after stroke, while the emotions are related more to the physical abilities.
Physical abilities, including muscle strength of the lower extremities, static balance, gait, and independence of ADL, were improved significantly in acute stroke patients over eight weeks. The stroke patients who participated in this study were in the early period of rehabilitation (weeks after stroke: three weeks (
n = 2); four weeks (
n = 2); five weeks (
n = 6); six weeks (
n = 7); seven weeks (
n = 6); and eight weeks (
n = 1)). Many studies reported that most stroke patients show considerable recovery of function over the first few months [
75,
76,
77,
78]. Recovery was reported to be fastest in the first few weeks after a stroke but suggests that it can continue beyond the first three months [
79]. Numerous studies showed significant increases in the muscle strength of the upper and lower extremities within the first few weeks or months after stroke [
80,
81,
82,
83]. Many studies reported that static balance, dynamic balance, and gait function were increased significantly within a few weeks or months after stroke [
79,
84,
85]. In addition, previous findings showed that the gain of ADL in stroke patients who participated in intensive rehabilitation was most significant during the first few weeks or months after a stroke [
86,
87]. Given all these findings, the muscle strength, static balance, gait function, and the independence of ADL appear to be improving in the first few weeks or months after stroke.
There were no significant changes in self-control, positive emotion, and negative emotion score in acute stroke patients during eight weeks. Hence, the self-control, positive emotion, and negative emotion levels in stroke patients were consistent over time. This was attributed to the emotional experience. No critical events, such as falls, serious changes in health condition, cognitive problem, or death of a family member, which could change the self-control, positive emotion, and negative emotion levels, occurred during the study. On the other hand, these results are inconsistent with those of a previous study. Seale et al. examined the changes in positive emotion over a three-month follow-up [
47]. They found that 35.6%, 29.2%, and 35.2% of participants reported an increase, a decrease, and no change in positive emotion, respectively [
47]. Other studies also reported that positive emotion is a dynamic process that can vary with time [
43,
88]. This study attributed these inconsistent results to the difference in environment. The previous study measured the emotion in stroke patients at discharge and the three-month follow-up. In contrast, the present study measured the emotions in stroke patients who were hospitalized. These differences in the environment may explain the inconsistent results between studies.
No significant correlation was observed between self-control and physical abilities (muscle strength of knee, static balance, gait, and ADL) at the baseline, four weeks, and eight weeks. Hence, high self-control level does not lead to better physical abilities in stroke patients. Previous studies reported that the physical abilities are determined by the stroke severity [
89,
90,
91], not the self-control level. From all these considerations, it was assumed that self-control is not related to the physical abilities of acute stroke patients.
In this study, a negative correlation was observed between the positive emotion score and COP sway velocity. On the other hand, there was no significant correlation between positive emotion score and knee muscle strength, gait variables, and the FIM score. These results mean that positive emotion is related to the static balance. The results of this study are consistent with previous studies. Previous studies suggested that positive emotions significantly affect the functional capacity measured by testing lifting, postural tolerance, and repetitive movement [
41,
42]. On the other hand, the mechanism of the correlation between positive emotion score and physical ability remains unclear. LaLumiere et al. reported that emotional stimulation influences the synaptic plasticity of the brain and descending tracts from the brain [
92]. This could affect the motor system. Given these findings, it was assumed that positive emotion is positively related to the static balance of acute stroke patients.
A negative correlation was observed between the negative emotion score and the knee strength. A positive correlation was noted between the negative emotion score and static balance variables (COP path length and COP sway velocity). A negative emotion was negatively associated with the gait variables (velocity, cadence, and affected side single support). A negative correlation was noted between the negative emotion score and the FIM score. These results mean that negative emotions are related to the knee muscle strength, static balance, gait, and independence of the ADL. These are consistent with previous studies. Studies found that negative emotions decreased the muscle strength and could adversely affect the physical function [
36,
40,
48,
49]. Other studies reported a negative correlation between depression and functional ability and motor skills in stroke patients [
93,
94]. From these considerations, it was assumed that the negative emotion is negatively related to the physical abilities of acute stroke patients.
The reason why negative emotion was more correlated with physical abilities than positive emotion was because of differences in measurement items. This study used the PANAS scale to examine the patient’s positive and negative emotions. The negative emotions in PANAS were composed of the following: upset, distressed, nervous, jittery, guilty, ashamed, hostile, irritable, scared, and afraid. The stroke patients experienced these feeling easily during hospitalization after stroke. The positive emotions in PANAS were composed of the following: interested, alert, attentive, excited, enthusiastic, inspired, proud, determined, strong, and active. The stroke patients might have difficulty feeling these emotions, such as inspired, excited, or enthusiastic, and these emotions are related to feelings that are not easy to experience during hospitalization regardless of the patient’s physical ability.
In this study, there was a significant positive correlation between the self-control score and the increases in knee muscle strength. A significant positive correlation was noted between the self-control score and the static balance improvement (COP sway velocity and weight bearing on the affected side). A significant positive correlation was noted between the self-control score and the increases of the gait variables (velocity and cadence). These results mean that the self-control level is positively related to the improvement of the knee muscle strength, static balance, and gait. Choi et al. examined the relative contributions of self-control and positive emotion on achievement. Across five studies (
n = 1130), they reported that self-control and positive emotions are important predictors of achievement [
33]. In addition, self-control is more strongly related to achievement than positive emotion. This finding holds for college students, middle-school students, East Asian adults, and North American adults, suggesting that it is cross-cultural and robust across age and measurement [
33]. Improvement of physical ability and functional recovery are important goals for stroke patients. Goal achievement, such as increasing muscle strength, balance, gait function, and independence of the ADL could be affected by the self-control level. A previous study reported that self-control is involved in managing stress, focusing attention on specific tasks, modifying the responses according to the needs, and planning and performing activities required to achieve long-term goals [
29]. Stroke patients could be motivated by their long-term goals. Many rehabilitation professionals commonly believe that patients’ motivation plays an important role in determining the outcome [
95,
96,
97,
98]. The motivation to achieve a goal, such as better walking and independence of ADL, could promote the physical recovery of stroke patients. For these reasons, stroke patients who have a higher self-control level tend to achieve their goal more than patients with a lower self-control level. In addition, many research findings showed that high self-control is related to better achievement in various areas such as physical health, substance dependence, higher scholastic performance, coping better with frustration and stress, personal finances, and criminal offending outcomes [
30,
31,
32]. Kim and Park reported that self-control has a significant, positive emotion on the ADL in stroke patients [
23]. This previous finding is consistent with the present study. From these considerations, the self-control level appears to be increasing the functional recovery after stroke. Given these findings, it was assumed that the self-control level is positively related to functional recovery in acute stroke patients over time. On the other hand, there was no correlation between the self-control level and the increases in FIM score. The FIM includes upper and lower extremity motor function items, and the upper limb function has a significant impact on the change in score on this test. However, in this study, three patients could not contract their upper extremity muscles in any of the tests, and there were no changes in the muscle strength over time. The three patients had relatively high self-control levels in the baseline (24, 26, and 36), four weeks (25, 25, and 37), and eight weeks (26, 27, and 37). It was assumed that this study was conducted with a small sample size, and the data from the patients could affect these results.
No significant correlation was observed between the positive emotion at the baseline and changes in physical variables during four and eight weeks. No significant correlation was observed between the negative emotion at the baseline and changes in physical variables during four and eight weeks. These results mean that positive and negative emotions are not related to the functional recovery. On the other hand, these results are inconsistent with those of a previous study. Ostir et al. examined the effects of positive emotions on the functional ability of stroke patients [
43]. Eight hundred and twenty-three stroke patients participated in the study at discharge and the three-month follow-up. A higher discharge positive emotion (high CES-D score) was significantly associated with higher motor and cognition FIM ratings and a higher total FIM rating after three months [
43]. These results indicate that positive emotions are associated with gains in functional status post-stroke. In people with stroke, increases in positive emotions over a three-month period were significantly associated with an increased likelihood of recovery of functional status [
47]. Kim and Park suggested that stroke patients who experience less depressed moods and stress have more self-control and maintain a higher ADL level [
23]. This study attributed these inconsistent results to the difference in measurement scale and environmental factors. Given the results, further discussion is needed to identity whether emotions affect the functional recovery in stroke patients.
In summary, this study found that the emotions were related to the physical abilities, while the self-control level was not. The self-control level is positively related to increased functional recovery in stroke patients over time. High self-control helps improve the knee muscle strength, static balance, and gait function after stroke.
This study had several limitations. First, the sample size was small, and there was no control group. Second, this study did not control the effects of the drug, rehabilitation quality, and environment. Third, this study did not include testing for depression and did not report physical conditions of the patients after stroke. Lastly, this study could not identify the long-term effects of self-control and emotions after eight weeks. Given these limitations, additional studies of the long-term effects, widening the subject range, and a well-controlled study will be needed.