Effect of Digital Therapeutics on Range of Motion, Flexibility, Dynamic Balance, Satisfaction, and Adherence: A Randomized Controlled Trial

Abstract

This study investigated the effect of digital therapeutics on ROM, flexibility, dynamic balance, satisfaction, and adherence. A sample of 34 volunteers was randomly assigned into a Digital Therapeutic Group (DTG) (n = 17) and a Non-Digital Therapeutic Group (NDG) (n = 17). The groups performed four calf muscle stretches and two hamstring stretches for 4 weeks. Flexibility and balance were evaluated to assess the effectiveness of the exercise program. A survey was conducted to assess subjects’ satisfaction, and exercise performance record papers and video records were assessed for exercise adherence. The paired t-test was used to compare the two populations before and after the program. The independent t-test was used to compare the change scores between groups. In the pre- and post-comparison within each group, the DTG group showed significant differences in all items except the dorsiflexion range of motion (ROM) (p < 0.05). The left straight leg raise (SLR) was significantly different (p < 0.05), and there was a significant difference in exercise satisfaction and participation between the two groups (p < 0.05). DTG showed improved flexibility, dynamic balance, and higher exercise satisfaction and adherence than NDG. The application, providing lower extremity stretching, can improve dorsiflexion ROM, flexibility of the lower extremity, dynamic balance, exercise satisfaction, and exercise adherence.

1. Introduction

Regular exercise is a key strategy to improve overall health, decrease the risk of musculoskeletal, metabolic, cardiovascular, and neurological conditions, and reduce all-cause mortality [1,2]. Despite these clear and well-known benefits of exercise, one-third of adults do not meet exercise guidelines [3], and low enjoyment during exercise, among other reasons, can be a powerful factor leading to exercise avoidance [4,5,6]. Common components of exercise include stretching [7], and flexibility is generally considered a necessary component of sports and fitness [8]. Lower extremity flexibility, especially, is important for successful performance of sports movements [9] and activities of daily living [10,11], and is essential for reducing the risk of injury [12,13]. Hamstring muscle shortening is a major risk factor for knee joint stiffness due to increased patella and femur compression, muscle dysfunction, and cartilage decline [14]. Gastrocnemius and soleus muscles play a major role in weight-bearing activities. Therefore, lower extremity stretching helps decrease leg pressure and cramping, increases range of motion (ROM) in the ankle joint, and improves dynamic balance through an improved ability to lower the center of mass, as well as changes in length and stiffness of muscle tendon units [15,16,17,18]. Additionally, long-term stretching programs can be an alternative to general strength training or rehabilitation exercises in cases where active force production is not possible due to limitations in joint movement [19].

Digital therapeutics (DTx) are evidence-based behavioral treatments delivered online that can increase accessibility and effectiveness of healthcare [20]. They are defined as evidence-based, clinically evaluated software to treat, manage, and prevent a broad spectrum of diseases and disorders [21]. DTx help to prevent, manage, and treat diseases using high-quality software programs. These evidence-based behavioral treatments are delivered online to increase healthcare access and effectiveness [20]. The advent of social media platforms, wearable devices, and cloud-based data platforms has garnered digital health worldwide attention. Health monitoring is gradually expanding from hospitals and treatment centers to the digital world [22].

Programs delivered online through DTx are recognized as a “secure arena” by users, which increases self-disclosure and honesty [23], and can improve physical functionality [24,25,26]. DTx can also enhance user satisfaction by enhancing usability, providing enjoyment and satisfaction, and improving quality of life through enhanced functionality [24,25,26]. Previous studies have shown that patient participation improves the quality of care, but programs that increase patient participation in exercise programs are lacking [27]. However, DTx allow providers to monitor patient adherence and enable patients to independently engage in treatments, providing quality, non-invasive care for a large population [28]. Home-based programs utilizing DTx can improve exercise adherence [26], especially through a push notification [29].

Recently, a digital therapeutic with a calf muscle and hamstring stretching training protocol was developed. There are many studies confirming the effectiveness of enhancing functionality through DTx; however, despite the impact of exercise satisfaction and adherence on exercise effectiveness, factors such as satisfaction with the exercise program, enjoyment, immersion in exercise, motivation for exercise, and exercise adherence lack sufficient research confirmation [27,30,31,32]. Low enjoyment during exercise contributes to physical inactivity and exercise avoidance in healthy adults [4,5,6], and despite the fact that DTx can provide exercise enjoyment [25], few studies have identified a correlation between DTx use and satisfaction in healthy adults. Additionally, few studies have identified pure adherence without researcher intervention [26]. Therefore, we sought to prove the effectiveness of DTx by equipping them with alarm functions, exercise guide videos, and exercise recording functions, and by eliminating the intervention of a therapist.

The purpose of this study is to investigate the effect of using a stretching application on range of motion, lower extremity flexibility, dynamic balance, exercise satisfaction, and exercise adherence in healthy adults. The hypothesis was that subjects using the stretching application would be more flexible and exhibit better dynamic balance with higher participation and satisfaction levels compared to those not using the application.

2. Materials and Methods

2.1. Study Design

This study employed a randomized controlled trial design. Subjects were randomly arranged into two groups using an Excel function, as follows: the Digital Therapeutic Group (DTG) and the Non-Digital Therapeutic Group (NDG). We followed the random allocation method of previous studies [33]. The Microsoft Excel 365 (Microsoft Corporation) program was used to generate a table of random numbers assigned to each subject. Each subject was numbered 1 to 34, and 32 random numbers between 0 and 1 were generated using the RAND () command in Excel. The random numbers were sorted from smallest to largest and sequentially assigned to two groups. The research protocol was approved by the Institutional Review Board (IRB) of Sun Moon University (approval ID: SM-202309-026-1), and the study was registered at the Clinical Research Information Service (CRIS, KCT0009123, date of registration: 19 January 2024). Informed consent was obtained from all participants, and all procedures were performed per the Declaration of Helsinki.

2.2. Participants

The study was conducted on 34 healthy adults, with 20 men and 14 women over the age of 20 who were enrolled at S University in Asan, Chungcheongnam-do. The subjects included those who (1) could use the application, (2) had no history of lower extremity disease (motor disorders, sensory abnormalities), and (3) had no history of spinal disease or surgical operation. Subjects in pain during the experiment were excluded after rest during the experiment. The study subjects were provided with a full explanation of the study purpose and methods, and participants provided written consent. All subjects measured their height using an automatic BMI measuring instrument (BSM 370, Republic of Korea, 2011) and their weight using a Body Composition Analyzer (InBody 570, Biospace, Republic of Korea, 2013) before participating in the study. A survey (A1. How often do you exercise, A2. How often do you stretch) was conducted to measure exercise amount, and responses were converted into scores (max of 9 points) [34].

Table 1. General characteristics of the subjects (N = 34).

	DTG (N = 17)	NDG (N = 17)	p-Value
Age (years)	20.41 ± 1.70	20.2941 ± 1.05	0.81
Height (cm)	169.41 ± 8.94	169.41 ± 7.97	1.00
Weight (kg)	66.29 ± 10.21	70.18 ± 18.53	0.46
UAE (score)	4.29 ± 2.20	3.71 ± 1.65	0.38

Values indicate mean ± standard deviation. DTG: Digital Therapeutic Group. NDG: Non-Digital Therapeutic Group. UAE: The Usual Amount of Exercise.

displays the participants’ characteristics.

2.3. Experimental Procedures

The research procedures were as follows (Figure 1): The stretching program was conducted over 4 weeks [35], and pre-training was conducted before the intervention began. No warm-up was performed to eliminate potential interactions between warm-up, stretching, and measurements [36]. Additionally, the researcher informed participants that the exercise was voluntary and there were no disadvantages to not participating. Data collection of specified outcome measures was conducted twice: once before and once after the intervention. All measurements were recorded by the same experimenter to avoid inter-tester variability and errors. Additionally, this study was single-blind, and the outcome assessor did not know who the subjects were, or which group they were assigned to.

2.4. Intervention

The experimental group voluntarily performed hamstring and calf stretching exercises at home using the application. The control group voluntarily performed hamstring and calf stretching exercises at home based on the pre-training content. The massage and stretching performed by both groups were the same. Each movement, performance time, and rest time were explained to both groups during pre-training. Details of the exercise program are described in

Table 2. Description of the exercises.

Muscle Group	Exercise Description
Calf muscles	In a seated position, identify the painful area of the calf muscle. Use a tennis ball to self-massage the area in circular motions for one minute [37].
	Stretch the gastrocnemius and soleus by hanging a towel on your foot and pulling it toward your body while in a seated position. Each set will consist of 15 s of exercise, with five sets in total, and a rest time of 5 s between each set [38].
	Stand and take a step forward while keeping both hands on the knee of the front foot with the upper body upright. Then, move the front knee forward while keeping the heel of the back foot (stretching leg) on the ground. Each set will consist of 30 s of exercise, with three sets in total, and a rest time of 10 s between each set [16].
	Take a step forward while keeping both hands on the knee of the front foot with the upper body upright. Then, bend the knee of the front leg (stretching the soleus of the back leg). After that, move the front knee forward (stretching leg) while keeping the heel of the back foot on the ground. Each set will consist of 30 s of exercise, with three sets in total, and a rest time of 10 s between each set [16].
Hamstring	Stand on the floor with both legs together. Then, bend the trunk forward to touch the hands to each foot. Each set will consist of 15 s of exercise, with five sets in total, and a rest time of 5 s between each set [16].
	Flex the hip joint of one leg to 90 degrees and fully extend the knee joint by fixing the towel on the foot in a standing position. Hold this motion for 15 s and repeat three times for both legs. Rest for 5 s between each set. For more stability, place the legs on a wall or chair [39].

and Figure 2.

DTx: Stretching Application

This study utilized an application involving calf muscle and hamstring stretching. After installing the application, subjects could create a profile by entering their name, gender, age, height, weight, and the presence of joint disease. Profiles were created anonymously. The application was equipped with an alarm setting function, allowing subjects to set smartphone push alarms at any time, and as many times as they wanted. A total of six movements to massage and stretch calf muscles and to stretch hamstrings were provided as videos through the application, and narration and subtitles were provided during video playback. After completing one movement, the subject had to press the ‘Next’ button to move on to the next movement. Subjects were able to verify how much and how often they performed the stretching exercises through the video playback records (Figure 3).

2.5. Measurements

Both groups underwent one measurement before the intervention and one after. The same researcher conducted all measurements and evaluations to reduce the error range. Measurements were taken for the toe touch test [40], range of motion (ROM) [16,35], Y-balance test [35], and straight leg raise (SLR) [41]. Exercise participation was assessed through exercise performance record papers and a video viewing record. A survey assessed participants’ satisfaction with the exercise program.

2.5.1. Toe Touch Test

The toe touch test was conducted using a 30 cm high box. Subjects climbed onto the box and reached towards their toes. They were instructed to stand with their knees straight and their legs together, with their feet positioned at the end of the box. They were required to keep their knees, arms, and fingers fully extended, with one hand on top of the other, in a maximum reach for approximately 6 s. The final position that the subjects reached was recorded as their test score. Reaches short of the toes were negative scores, and those beyond the toes were positive scores [40] (Figure 4).

2.5.2. The Y-Balance Test

The Y-balance test measures dynamic balance and flexibility in the lower extremities. The test involves standing on one leg and reaching as far as possible with the other leg in the following three directions: anterior (forward), posteromedial (inside), and posterolateral (outside). The maximum distance reached is recorded and expressed as a percentage of the subject’s leg length. The test is repeated three times, and the average value is recorded. A trial was classified as invalid if the participant removed their hands from their hips, did not return to the starting position, applied sufficient weight through the reach foot to increase reach distance, placed the reach foot on the ground on either side of the line or tube, raised or moved the stance foot during the test, or kicked the plate with the reach foot to gain more distance. If an invalid trial occurred, the data were deleted, and the participant repeated the trial [35,42] (Figure 5).

2.5.3. The Straight Leg Raise (SLR)

Participants were in a supine position with their hip stabilized by a tester to avoid lumbopelvic compensatory action. They flexed their hip with the knee extended and the ankle relaxed until the maximal ROM was reached. A second tester measured the hip flexion angle using a goniometer. The axis of the goniometer was placed on the greater trochanter, and the fixed arm was placed on the femur of the non-tested leg. The movement arm was placed on the lateral side of the femur. Three trials were performed on each lower limb, and the highest value was used for analysis [41,43] (Figure 6).

2.5.4. Range of Motion (ROM)

A goniometer (CCC > 0.98) was used to assess the dorsiflexion angle in the ankle joint [44]. The subjects were instructed to sit on a bed with their legs not touching the ground. They then relaxed their ankle joint and maintained a neutral position of 90 degrees. The goniometer axis was placed on the outer malleolus, and the fixed arm was placed on the fibula. The movement arm was placed on the side of the foot sole relative to the fifth toe. The angle was measured with the subjects in a comfortable state, and the maximum dorsiflexion angle was recorded [16,35,45] (Figure 7).

2.5.5. Questionnaire Assessing Satisfaction

We conducted a 10-item questionnaire after the intervention, surveying the test group’s satisfaction with the application. These items included the following: (1) The stretching time was appropriate; (2) The stretching strength was appropriate; (3) The stretching movement was not difficult or confusing; (4) As I progressed the exercise, I performed the movement properly; (5) During the exercise period, I could steadily perform the stretching exercise; (6) After the exercise period, I felt like I should exercise steadily in the future; (7) Stretching changed my body; (8) I was able to concentrate until the end of the stretching time; (9) I recommend this exercise program to others; and (10) Please choose the level of enjoyment you felt during the stretching program as your score. The patients answered the questionnaire based on a 10-point Likert scale of 1 to 5, with scores indicating the patients’ response (strongly disagree, disagree, neither agree nor disagree, agree, and strongly agree). A self-developed questionnaire was used, and questions from surveys in previous studies were modified to suit the study’s purpose [46,47,48].

2.5.6. Exercise Adherence

Exercise adherence was evaluated through exercise performance record papers and video viewing records. The group that did not use the application was given an exercise performance record sheet and instructed to mark whenever they engaged in stretching. The group using the application performed the exercise when they watched the entire stretching video in the application. Therefore, we evaluated participation by checking the application’s video viewing records. Evaluations of both groups were conducted anonymously. The exercise program was carried out without any intervention so that it could be performed voluntarily. The adherence score was calculated by scoring the number of days the subject participated in exercise out of the intervention period of 28 days (e.g., a participant who stretched on 14 days scored 14 points) [49].

2.6. Sample Size Estimation

Based on the results of a previous study (Jose M., 2012), the mean variation of the toe touch test score in the control group was −1.21 cm, and in the test group it was 4.59 cm [40]. Therefore, it was assumed that the difference between the variation in the two groups was 5.8, and the standard deviation was the largest by a conservative approach of 000 [40]. Using this effect size, including a type I error rate of =0.05 and a type II error rate of =0.2 (corresponding to statistical power of 80%), it was determined that 15 participants were required per group. To conservatively account for a 10% attrition rate, 17 participants per group were needed to obtain statistically significant results. Therefore, this study required a total sample size of 34 participants.

2.7. Data Analysis

All statistical analyses were calculated using the SPSS 29.0 statistical software program. The distribution of the data was evaluated using the Shapiro–Wilk test, skewness, and kurtosis, and it was confirmed that the data followed a normal distribution [50]. For demographics such as age, gender, height, and weight, technical statistical values such as mean and standard deviation (SD) were obtained. The pre-identity of the categorical variables was analyzed using the chi-square test, the mean standard deviation of the evaluation variables, and survey results (Likert rating scale). The differences before and after the exercises were analyzed using a paired t-test. The differences in continuous variables between groups were analyzed by the independent t-test. Prior homogeneity was verified through cross-analysis. All statistical tests were two-sided and evaluated as valid when the probability of significance was p < 0.05.

3. Results

Homogeneity was confirmed in the pre-assessment between groups (p > 0.05). No subjects were excluded. In the pre- and post-comparisons within the groups, there was a significant difference in both groups in the Y-balance test and the toe touch test (p < 0.05). For ROM, only the right dorsiflexion of the NDG demonstrated a significant difference (p < 0.05). For SLR, only the right SLR of the NDG did not show a significant difference (p > 0.05). In the comparison of changes between the two groups before and after the intervention, there was a significant difference only in the left SLR (p < 0.05) (

Table 3. Changes in outcome measures and the difference between pre- and post-intervention (0 to 4 weeks).

Measures		DTG (n = 17)				NDG (n = 17)				p-Value between Group
		Pre-Mean (SD)	Post-Mean (SD)	Difference Mean (SD)	p-Value	Pre-Mean (SD)	Post-Mean (SD)	Difference Mean (SD)	p-Value
Toe Touch Test		2.19 ± 9.00	7.15 ± 8.88	4.96 ± 4.70	<0.001	−0.977 ± 12.46	3.99 ± 11.16	4.97 ± 4.09	<0.001	0.997
Y-Balance	Lt	89.23 ± 11.71	95.41 ± 11.20	6.19 ± 4.43	<0.001	93.96 ± 7.69	98.53 ± 8.69	4.57 ± 3.42	0.003	0.349
	Rt	89.93 ± 13.36	96.80 ± 11.04	6.87 ± 4.68	<0.001	92.44 ± 8.26	99.05 ± 9.58	6.61 ± 5.86	<0.001	0.890
SLR	Lt	60.88 ± 13.02	72.47 ± 11.51	11.59 ± 5.22	0.000	66.77 ± 14.89	72.65 ± 13.24	5.88 ± 10.04	0.028	0.048
	Rt	59.71 ± 16.44	69.12 ± 13.14	9.41 ± 6.59	<0.001	64.71 ± 12.05	70.88 ± 14.28	6.18 ± 14.09	0.09	0.400
ROM	Lt	14.82 ± 4.57	16.12 ± 3.35	1.29 ± 3.69	0.167	14.12 ± 4.05	15.47 ± 3.79	1.35 ± 4.66	0.249	0.968
	Rt	15.06 ± 4.56	16.53 ± 3.94	1.47 ± 4.16	0.164	14.49 ± 2.81	17.24 ± 4.67	2.65 ± 3.90	0.013	0.401

DTG: Digital Therapeutic Group. NDG: Non-Digital Therapeutic Group.

). In the intragroup comparison, DTG showed a change from 60.88 to 72.47 in the left straight leg raise (SLR), while NDG changed from 66.77 to 72.65. Therefore, in the intergroup comparison of pre–post change, DTG exhibited a result of 11.59, whereas NDG had 5.88. In other words, DTG demonstrated greater improvement in left SLR compared to NDG.

There was a significant difference in satisfaction and participation in the lower extremity stretching program between the two groups (p < 0.05) (

Table 4. Comparison of satisfaction with and adherence in the stretching program between groups.

	Mean (M) ± Standard Deviation (SD)
	DTG	NDG	T	p-Value
Satisfaction questionnaire	41.18 ± 4.29	36.88 ± 4.76	2.77	0.009
Exercise adherence	8.00 ± 3.97	5.18 ± 3.71	2.14	0.04

DTG: Digital Therapeutic Group. NDG: Non-Digital Therapeutic Group.

). There was no significant difference in “A1”, “A2”, “A5”, “A7”, “A9”, and “A0” (p > 0.05), but there was a significant difference in “A3”, “A4”, “A6”, and “A8” (p < 0.05) (

Table 5. Survey questionnaire for exercise satisfaction.

Survey Question		Mean (M) ± Standard Deviation (SD)
		DTG	NDG	T	p-Value
A1	The stretching time was appropriate.	4.24 ± 0.66	3.82 ± 0.95	1.46	0.153
A2	The stretching strength was appropriate.	4.35 ± 0.61	4.06 ± 0.83	1.18	0.246
A3	The stretching movement was not difficult or confusing.	4.76 ± 0.44	4.41 ± 0.62	1.92	0.03
A4	As I progressed in the exercise, I was performing the movement properly.	4.35 ± 0.49	3.88 ± 0.99	1.75	0.045
A5	During the exercise period, I could steadily perform the stretching exercise.	3.53 ± 1.12	2.88 ± 1.32	1.54	0.67
A6	After the exercise period, I felt like I could steadily exercise in the future.	4.12 ± 0.99	3.59 ± 0.80	1.72	0.048
A7	Stretching changed my body.	3.53 ± 0.87	3.47 ± 0.80	0.21	0.42
A8	I was able to concentrate until the end of the stretching time.	4.06 ± 0.75	3.24 ± 1.03	2.66	0.006
A9	I recommend this exercise program to others.	4.29 ± 0.59	4.00 ± 0.61	1.43	0.08
A0	Please choose the level of enjoyment you felt during the stretching program as your score.	3.94 ± 0.83	3.53 ± 0.94	1.35	0.09

A: Numbers on the survey questionnaire. DTG: Digital Therapeutic Group. NDG: Non-Digital Therapeutic Group.

). In the comparison of satisfaction questionnaire between the groups, DTG scored 41.18 points, whereas NDG scored 36.88 points, indicating higher satisfaction with DTG. Further analysis of the satisfaction survey revealed that DTG outperformed NDG in stretching performance accuracy, change in perception of stretching, and concentration during stretching. Additionally, In the comparison of exercise adherence between groups, DTG participated in exercise more frequently with 8 sessions, while NDG had 5.18 sessions.

4. Discussion

We used the toe touch test, Y-balance, SLR, and dorsiflexion ROM to determine the effectiveness of 4 weeks of lower extremity stretching application. In the pre- and post-test comparisons within groups, the group that used the stretching application (DTG) showed significant differences in all items except dorsiflexion ROM, while the group that did not use the stretching application (NDG) showed significant differences in all items except right SLR and left dorsiflexion ROM. There was a significant difference in right dorsiflexion ROM in NDG. However, in a previous randomized controlled study of 89 participants over 6 weeks, no significant differences in dorsiflexion were found, despite the larger mean differences in dorsiflexion. The pre- and post-difference in NDG may not be interpreted as a significant difference [51]. The SLR is a highly reliable and precise test that helps determine hamstring length and flexibility [52]. There was a significant difference in the left SLR between the groups. Hamstring stretching should take about 5 to 6 weeks to be effective [53]. The effect of short-term stretching is evident in the non-dominant legs [54]; in all subjects, the right leg was the dominant leg. As the study was conducted for 4 weeks, good results could not be obtained for both the dominant and non-dominant legs. However, if subjects continue to utilize the application, their flexibility will improve in both the dominant and non-dominant legs. Y. Choi (2019) found that self-exercise using an application affected change within groups, but not between groups, which is in line with these results [55].

Satisfaction with the application is an antecedent of engagement [56], and satisfaction with the exercise influences exercise adherence [30,31,32]. Therefore, a survey was conducted to evaluate satisfaction with the exercise program. The results of this survey were consistent with previous research, in that the group that used the application was more satisfied with the stretching program [55]. Significant differences were found in the stretching performance accuracy, change in perception of stretching, and concentration when stretching. Subjects using the application can be more immersed in their movements and perform them accurately, potentially altering their perception of stretching. Therefore, using the application can increase subjects’ satisfaction with the exercise program. Currently, there is no standard evaluation scale to assess exercise satisfaction, and survey items vary depending on the researcher and study characteristics. Since this study utilized a self-produced questionnaire, studies using other applications may not yield similar results.

To encourage voluntary participation in the lower extremity stretching program, it was conducted anonymously without any coercion. Unlike previous studies [26], there was no intervention by the therapist in using the application, except for alarms set by the subjects themselves. The group that used the application had higher exercise adherence. Therefore, exercise adherence when using the DTx will increase, and this is considered to have an impact on exercise effectiveness [29].

The main finding of this study is that stretching application improves flexibility of the lower extremity and dynamic balance, satisfaction, and compliance in healthy adults. Previous studies have shown that satisfaction with exercise influences adherence [30,31,32,56], and exercise adherence influences exercise effectiveness [25]. Therefore, this suggests that using a lower extremity stretching application with an alarm function can improve user satisfaction and adherence, thereby improving exercise effects such as flexibility of the lower extremity and dynamic balance. These results also raise the possibility that the use of a stretching application may improve physical inactivity and exercise avoidance in healthy adults, which may have important implications for future exercise behavior [4,5,6]. Furthermore, using stretching applications can improve users’ quality of life in social restrictions such as the COVID-19 pandemic (as well as future lockdown situations) [57], and the stretching application with high retention and adherence levels suggests that it may also be applicable to adults with musculoskeletal pain [57,58].

This study has several limitations. First, some of the subjects demonstrated a lack of motivation to perform the stretching. This voluntary study involved adults who do not frequently exercise. Therefore, subjects in the DTG who did not want to stretch may have struggled to exercise consistently or found the stretching time and intensity inappropriate. These results are evident in the satisfaction survey items. Additionally, although there was a significant difference in participation between groups, the DTG demonstrated a twice-weekly participation rate. This may be due to the nature of the program, which involves voluntary exercise performance without coercion. The results may improve with more appropriate motivation. Second, the intervention was applied over 4 weeks. Stretching must be performed at least twice a week for 5 to 6 weeks to see significant effects [53]. The study period may not have fully reflected the effect of stretching. The subjects may not have felt changes in their bodies due to the reduced stretching frequency and study period. Third, despite the request to fill out exercise performance records honestly, potential problems such as failure to record sessions, falsified data, poor memory leading to inaccurate data, etc., may occur. Fourth, this study was small in scale; therefore, the results of this study may vary if conducted on a large scale. Fifth, the validity and reliability of the satisfaction questionnaire has not been verified.

Future studies can apply DTx to the older population, clinical population, and athletes, and should investigate more variables such as strength, endurance, kinesthesis, proprioception, and functional status. Additionally, injury prevention needs to be measured directly to demonstrate a correlation between the use of stretching applications and injury prevention. Finally, the effectiveness of long-term stretching applications needs to be proven, and large-scale studies are needed.

5. Conclusions

Digital therapeutics (DTx) have a positive impact on exercise effectiveness, satisfaction, and participation. The research findings demonstrate that utilizing DTx for lower extremity stretching can have a positive impact on the flexibility of lower extremities, satisfaction, and participation. As a result, performing stretching using DTx in healthy adults may improve exercise effectiveness by increasing satisfaction and adherence. These results may serve as valuable references for those interested in sustained participation and increased satisfaction with stretching using DTx.