Abstract
BACKGROUND:
Elastic taping that applies shear force affects joint movement. However, it remains uncertain whether elastic taping or stretching is more effective in improving flexibility.
OBJECTIVE:
We investigated whether elastic taping for flexibility improvement is comparable to traditional stretching.
METHODS:
In this randomized controlled trial, 64 university students were randomly allocated to two groups: elastic taping on the sole or 30 s of static stretching. The primary outcome measures were the straight leg raising angle, tested with an equivalence margin (
RESULTS:
The mean differences in straight leg raising between the two groups after the interventions were not greater than the equivalence margin (mean [95% CI]: 1.4 [
CONCLUSION:
Elastic taping augments the flexibility-improving effect comparable to static stretching, based on an equivalence margin. Elastic taping of the sole appears to be an alternative method of improving flexibility.
Keywords
Introduction
The hamstrings are biarticular muscles composed of Semitendinosus, Semimembranosus, and Biceps Femoris, and are anatomically characterized by having fusiform muscles or long tendons [1]. Decreased flexibility of the hamstring muscles increases the risk of tendon injuries. Therefore, clinicians should target treatments to the hamstring muscles. Stretching is one approach to improving muscle flexibility. There are various methods of stretching, such as dynamic, static, loaded progressive, ballistic, and proprioceptive neuromuscular facilitation stretching, that can be used to achieve this goal [2, 3]. Static stretching is a popular method because it requires less time and effort, has a lower risk of injury, and has shown positive results in improving flexibility [4, 5, 6, 7]. There is a consensus that static stretching is effective in increasing the flexibility of the hamstring muscles in healthy young adults [8]. Stretching intensity is considered an important variable for improving flexibility, and stretching exercises with an intensity of approximately 50% of the maximum pain and discomfort felt decrease the risk of injury [9]. However, static stretching not only causes acute pain due to the passive stretching of muscles but also has the disadvantage of acutely deteriorating performance, such as in sprint running and jumping height [10]. Fauris et al. reported that plantar fascial interventions most affected hamstring flexibility [11] Previous studies [12] have shown that a 4-min myofascial release to the sole improves hamstring muscle flexibility. A recent systematic review and meta-analysis reported that myofascial intervention has a remote effect on the range of motion (ROM) [13]. The application of elastic tape has been reported to reduce muscle stiffness and pain [14, 15]. Applying shear force with the application of an elastic tape also affects the movement of joints [16, 17]. Applying elastic tape to the sole for the purpose of the fascia effect may improve the ROM of the joint immediately and remotely, without causing pain in the hamstring muscles. However, no randomized controlled trial that compares the safety and efficacy of static stretching and easy-to-operate, pain-free elastic taping has been published to date. Determining whether elastic taping can immediately improve ROM is beneficial in clinical practice. In this study, straight leg raising (SLR), which is an index of hamstring muscle flexibility, was used as one of the primary outcomes, and the non-inferiority/equivalence effect of elastic taping on static stretching was evaluated.
Materials and methods
Study design
A randomized parallel-group clinical trial was conducted to investigate whether elastic taping improves flexibility as quickly as static stretching. This trial has been designed according to the CONsolidated Standards Of Reporting Trials (CONSORT) statement [18], and is reported according to the Template for Intervention Description and Replication (TIDieR) checklist [19]. Participants were assigned to either the static stretching group or the elastic tape group. The SLR angle and fingertip-to-floor distance (FFD) were set as the primary outcomes of flexibility. In addition to these performance abilities, the degree of pain during the intervention was assessed as a secondary outcome.
Participants
Participants consisted of physically active university students, and the following exclusion criteria were applied: Those who have reported 1) lower limb injury in the past 6 weeks; 2) lumbar spinal injury or surgery in the last 6 weeks; and 3) lower limb surgery within the last 6 months and major ligament surgery within the previous year. Participants were recruited from students belonging to one university, and the volunteers were recruited using a bulletin board. This research was conducted at a private medical university in the Kanto area of Japan. Sixty-five participants were screened in June 2021 (Fig. 1). Finally, 64 students were enrolled in this study (31 men and 33 women, average age: 20.9 years).
Demographic data of participants
Demographic data of participants
m, male; f, female; Values are expressed as mean
Flowchart showing study participants’ enrollment. SLR, straight leg raising; FFD, fingertip-to-floor distance; HFS, hip flexor strength; KES, knee extensor strength; TSD, two-step distance; VAS, visual analog scale.
Elastic taping protocol.
Participant allocation was set so that the ratio of the static stretching group to the elastic tape group was 1:1. An online statistical computer program (Graph Pad Software, USA,
Interventions
Participants assigned to the static stretching group were prescribed static stretching of the hamstring muscles. One researcher individually instructed the participants about the stretching procedure. The stretching method was as follows: the crouching state was the starting posture, the knee was gradually extended while keeping the front of the thigh and the front of the chest in contact, and finally, the buttocks were raised as much as possible. Stretching interventions were held only once for 30 s, with the buttocks raised as much as possible.
For the participants assigned to the elastic tape group, kinesiology tape (NK-50, Nitto Denko, Osaka, Japan) cut to 50% of the foot length was applied on the sole of the dominant foot. The kinesiology tape was devised so that it was extended 1 cm from its natural length during its application and was applied from the tip of the toe to a position 3 cm behind the heel; the tape was applied by a physical therapist (Fig. 2). Elastic tape was applied individually by the same therapist. The application was performed in a long sitting position. The elastic tape was applied once after baseline assessment and removed after follow-up assessment. All participants assigned to the elastic tape group received the same intervention. No modification occurred in the intervention. Because all participants consented to a single intervention, no assessment of intervention adherence or fidelity was planned. Different sets of participants were assigned to the groups, and the allocation of participants was concealed by central computerized randomization.
FFD mesurement.
Difference in SLR from baseline to each follow-up between elastic tape and static stretching groups. M 
The SLR angle, which is one of the primary outcomes, was measured with the participants in the supine position. The angle was measured at which the dominant leg was raised as much as possible with the fully extended knee. A digital inclinometer smartphone application (Clinometer, Tokyo, Japan,
In addition to the performance abilities of hip flexor strength (HFS), knee extensor strength (KES), and two-step distance (TSD), the degree of pain during the intervention was assessed as a secondary outcome. Muscle strength, including HFS and KES, was measured using a handheld dynamometer (
Data analysis
These data were analyzed using the intention-to-treat methodology developed for randomized controlled clinical trials. To verify that the effects of elastic taping and static stretching on SLR, which is one of the primary outcomes, were equivalent, we calculated 95% confidence intervals (CIs) for the difference between the two groups.
We then tested the following null (H0) and alternative (H1) hypotheses as ME: mean value of SLR after applying elastic tape is attached, MS: mean value of SLR after performing static stretching, and
We calculated the sample size for the primary outcome of change in SLR with a significance level of 5%, a power of 90%, and a standard deviation of 10.57, based on a previous study. Each group included 32 participants. In addition, the values of secondary outcomes were analyzed using Student’s unpaired t-tests or Mann-Whitney U tests, depending on the data’s distribution. Normality was confirmed using the Kolmogorov–Smirnov test. SPSS Statistics Ver. 26 (manufactured by IBM, Tokyo, Japan) was used for statistical analysis, and the significance level was set at 5%.
Results
One of the screened 65 students had a history of knee ligament surgery within the past year and was, thus, excluded. None of the participants in this study dropped out at the end of the post-intervention outcome measurement. No participant changed their originally assigned groups; 32 participants in each group received the intended treatment and the same number was used to analyze the outcomes. There were no changes in the outcomes after the start of the trial.
Physical performance at baseline in the two groups
Physical performance at baseline in the two groups
CI, confidence internal; SLR, straight leg raising; FFD, fingertip-to-floor distance; HFS, hip flexor strength; KES, knee extensor strength; TSD, two-step distance; Values are presented as mean
Comparison of clinical outcomes after intervention between the two groups
CI, confidence interval; SLR, straight leg raising; FFD, fingertip-to-floor distance; HFS, hip flexor strength; KES, knee extensor strength; TSD, two-step distance; Values are presented as mean
There were no significant differences in the outcome measures, including the SLR, FFD, muscle strength, and TSD, at baseline between the two groups (
The results of a non-inferiority/equivalence test for the SLR showed that the 95% CIs of the difference in the SLR between the two groups after the intervention did not exceed the non-inferiority/equivalence margin, indicating elastic taping equivalence (mean difference,
The NRS, which indicates the degree of pain during the intervention, was 2.6
This randomized controlled trial investigated whether elastic taping was as effective as static stretching for immediate effects of increased flexibility within a certain equivalence margin in Japanese university students. We found that the mean difference in SLR, an indicator of flexibility, between the two groups was within the equivalence margin and was not statistically different, suggesting that elastic taping has the same effect on flexibility improvement as static stretching.
Our findings showed that static stretching for 30 s increased the SLR by 6.2∘ (95% CI, 2.9∘ to 9.5∘), and elastic taping increased the SLR by 6.3∘ (95% CI, 3.6∘ to 9.1∘). The positive lower bound of the 95% CI for both interventions indicates that both interventions improved SLR. In a previous study of university students, an improvement in SLR of approximately 7∘ was reported as an acute effect of stretching on the hamstring muscles [20]. The effects of static stretching in our study were similar to those reported previously. It has been shown that there is no difference in the improvement of flexibility between stretching for 30 s and longer intervention times [21]. The stretching intervention time in this study was sufficient to improve flexibility. Therefore, considering the intervention time and effect, it can be inferred that the stretching intervention in this study was an appropriate treatment for comparing the flexibility-improving effect with other interventions.
Previous studies investigating the efficacy of elastic taping have shown pain relief and ROM improvement [22, 23, 24]. Improvements in the ROM may be associated with pain relief, as these reports used tapes for participants who felt pain. The effects of elastic taping on healthy people without pain include the promotion of muscle activity [25] and improvement of endurance [26]. A systematic review showed that there is a lack of compelling evidence to enhance performance abilities including muscle strength, balance, and agility [27]. The results of this study revealed that elastic taping remotely increases ROM to distant body parts, similar to that of myofascial intervention [12, 13]. However, it is still difficult to elaborate on our results based on the knowledge of the specific mechanism of elastic tape, which has not been fully elucidated. Richard et al. [28] quantified the movement of the skin during joint movement and found a relationship between joint movement and skin flexibility. We believe that promoting skin movement using elastic tape as well as a myofascial intervention may remotely increase ROM to distant body parts. In a previous study by Ito et al., the application of elastic tape to the sole of the foot improved ankle dorsiflexion, but hamstring flexibility was not assessed [29]. The effects of taping on the sole on hamstring flexibility may be due to the continuity, overlapping and compartmentalization of the muscular tissue by the fascia. A possible reason for the good results of the elastic tape on the sole is the the significant fascial continuity, via the Achilles tendon, between the plantar fascia and the posterior part of the sural fascia [30, 31].
Furthermore, the degree of pain during static stretching was significantly higher than that during elastic taping. The result that applying elastic tape did not induce pain in any of the participants is very useful information. It has been reported that static stretching induces pain during an intervention and that the intensity of static stretching changes the acquisition of flexibility [9]. Excessive stretching to gain flexibility causes discomfort, and pain [32]. With regard to performing the stretches in this study, subjects were instructed to perform at half the intensity of unbearable pain. Nevertheless, the fact that there was a significant difference in the degree of pain between the two groups suggested that stretching was a considerable pain-causing intervention for gaining flexibility. Based on the results of this study, it was clarified that elastic taping can be used as an alternative therapeutic modality that is pain-free and easily feasible to increase hamstring muscle flexibility or improve the ROM.
In this study, elastic taping did not reduce performance abilities. Elastic taping reduces pain and inflammation and promotes muscle function in patients experiencing pain [33]. However, there are some reports that elastic tapes for healthy populations do not affect postural balance, muscle circulation, and muscle strength [34, 35, 36]. Therefore, it is inferred that muscle function is not promoted in healthy people without pain. In this study, static stretching did not affect performance abilities, such as HFS, KES, and TSD. Static stretching has been reported to reduce performance abilities, such as jump height [37] and muscle strength [38]. However, we speculate that 30 s of stretching a single muscle group does not reduce performance. This is because Cornwell et al. [37] set an intervention time of 5 min and Yamaguchi et al. [38] set an intervention time of 20 min. Although passive torque and activity level decreased during 30 s of static stretching, it was shown that both recovered to the same level immediately after stretching [39, 40]. We speculate that mechanical and neurophysiological changes do not occur until after the intervention with 30 s of static stretching alone, resulting in poor performance. Given the equivalence of elastic taping with short-time static stretching and the reduced pain, elastic taping is an excellent treatment.
This study has some limitations. First, the primary endpoint of this study was immediately after the intervention. The interpretation of the results is limited because the lasting effects have not been followed up. Second, because we only studied healthy university students, the effects on athletes and the elderly are also unclear. Further verification is needed to increase external validity and applicability. Finally, the clinically important difference in flexibility improvement by static stretching in healthy individuals is not clear. The lower bound of the 95% CI for the effect of the SLR associated with elastic taping was 3.6∘. The magnitude of the effect on this number is unknown, and reference to the magnitude of the effect requires careful judgment. This study provides evidence for the efficacy of elastic taping to improve flexibility.
Conclusions
Elastic taping on the sole of the foot was found to be a useful intervention that immediately improves the flexibility of the hamstring muscles and hip joint ROM without causing pain. This suggests that it could be used as an alternative therapeutic modality for static stretching.
Author contributions
All authors contributed to the conception and design of the study. Material preparation, data collection, and analysis were performed by Tatsuya Igawa and Riyaka Ito. The first draft of the manuscript was written by Tatsuya Igawa, and all authors commented on the previous versions of the manuscript. All authors read and approved the final manuscript.
Data availability statement
The data that support the findings of this study are available from the corresponding author (Tatsuya Igawa) upon reasonable request.
Ethics statement
This study was approved by the ethics committee of the International University of Health and Welfare (IRB: 21-Io-6) and all research procedures were carried out in accordance with the Declaration of Helsinki. The study was registered with UMIN-CTR (UMIN000044525).
Funding
The authors report no funding.
Informed consent
Written informed consent was obtained from all participants before participation in the study.
Footnotes
Acknowledgments
The authors have no acknowledgments.
Conflict of interest
The authors declare that they have no conflict of interest.
