Ⅰ. Introduction
Stretching exercise increases flexibility by actively or passively stretching muscles, joints, and tendons, increases the structure of pathologically shortened soft tissue, and reduces the likelihood of injury, thereby contributing to effective muscle strength and high skill acquisition (Guissard & Duchateau, 2006). Also, stretching is a good warm-up method to prevent injury by relaxing the muscles by stretching the length berfore performing the main exercise (Smith, 1994).
Until now, stretching has been known to improve exercise performance and flexibility by facilitating blood circulation and properly increasing muscle temperature (Woods, Bishop, & Jones, 2007). However, while continuous ankle stretching can benefit from increased joint range by relaxing the length of the ankle muscles and stiffness of the surrounding tissues, incorrect stretching may cause temporary changes in tension and body sensitivity, which can cause balance problems if tissue changes, such as sports athletes (Weppler & Magnusson, 2010).
At the same time, flexibility, defined as the range of motion of the joint and evaluated as a ligament or muscle function surrounding the joint area is a fundamental element of the efficiency and exercise performance of human activities in daily life (Gleim & McHugh, 1997). Therefore, stretching is indispensable for not only physical strength, such as quickness, agility, muscle strength, and balance, but also athletic performance because excessive loss of flexibility can cause serious damage in motor performance.
Balance refers to the ability to regulate the center of gravity (COG) to remain within the base of support (BOS), which is maintained through dynamic interventions and environmental factors of internal and external forces (Pollock, Durward, Rowe & Paul, 2000). If the COG is out of BOS, more muscle activity is required to recover to a stable position, and in this situation, the compensatory posture strategy uses a visual, somatosensory, and vestibular system to modulate body segments to return the center of gravity to a stable position within the base (Grace Gaerlan, Alpert, Cross, Louis, & Kowalski, 2012). Especially, ankle strategy is routinely used during there is little perturbation on support surface to restore the balance of standing position by muscle contraction surrounding the ankle joint.
Among the various body parts in particular, the ankle joint contributes greatly to somatosensory system, while requiring the most complex motor control, and is the most vulnerable to sports damage (Toledo & Barela, 2010). In addition, clinical verification of effective stretching is required as an intervention method to improve pre-match performance and prevent injury in sports fields. Therefore, this study aimed to investigate the immediate effect of dynamic or static stretching applied to the ankle on the balance ability to effectively guide exercise within a limited time of treatment in clinical practice.
Ⅱ. Methods
1. Participants
The sample size was calculated according to th result of a previous study with an effect size of 1.48, assuming α=0.05, power of 80%, so a sample size of 9 patients per group would be required by G Power 3.1.9.7. Therfore, twenty healthy adults (age: 23.32±2.23) participated in this study. Participants were excluded from those with surgical experience in ankle joints and those with orthopedic diseases. All participants voluntarily agreed to participate in the study after fully listening to the explanation of the purpose and method of the study before the experiment.
2. Experimental procedures
All participants randomly assigned to two groups before the experiment. After then, they performed different stretching exercises. One group that performed static stretching exercises maintained stretching for 30 seconds after bending the sole of the foot and bending the back of the foot by hand and conducted three times at a 10-second break interval. Whereas, the other group that performed dynamic stretching exercise performed by moving the soles of the feet and the back of the feet back and forth for 30 seconds with hands. It was conducted a total of three times with a 10-second break interval. The groups measured balance ability before and after performing each stretching exercise.
3. Balance ability measurement
In this study, to measure balance ability, Good Balance System (Metitur, Finland) was used to find out the balance. The Good Balance System was used to measure the distance and velocity of the participant's posture sway in a standing position. Based on these coordinate values for x and y (i.e. the extent of mediolateral (ML) movement of the center of pressure (COP), the extent of anteroposterior (AP) movement of the COP), (1) the average speed of COP movement in the AP direction (mm/s), (2) the average speed of COP movement in the ML direction (mm/s), and (3) the average postural sway speed (mm2/s) were calculated. Postural sway speed is defined as the average horizontal area covered by the motion of the center of force per second (AP and ML direction). The force platform was an equilateral triangle (800 mm) and connected to a three-channel DC amplifier. The signal from the amplifier was converted to digital form using a 12-byte converter (waveform frequency = 50Hz) and stored on a personal computer's hard disk. Participants standed on the force plate in a natural and comfortable position while maintaining a distance between heels of 5 to 6 cm during balance measurement, and to maintain a posture of fixing the gaze to the mark on the front wall for 30 seconds.
4. Statistical analysis
The data analysis was statistically processed using SSPS ver 19.0, and the paired t-test was used to compare the difference before and after the experiment within each group. In order to analyze the difference between groups, the independent t-test was performed. Statistical significance probability was set to p=.05.
Ⅲ. Results
1. Pariticpants
As a result of performing the homogeneity test, no significant difference was found between groups (Table 1).
2. Balance ability according to stretching techniques
After static and dynamic stretching exercises, there were no significant differences in within and between groups for average AP speed, average ML speed, postural sway speed, Extent in AP direction, and Extent in ML direction (Table 2).
Ⅳ. Discussion
Traditionally, balacne ability refers to the ability to maintain a stable posture flexibly against dynamic enviromental changes without falling while supporting weight. Therefore, balance is an essential factor for daily life and all functional activities, and unstable balance ability limits the performance of various challenging activities in daily life and reduces the amount of activity by causing fear of movement (Maki & McIlroy, 1996). Furthermore, the reduced amount of activity again causes a decrease in balance, creating a continuous vicious circle that induces falls.
This study was conducted to find out the immediate effect of static and dynamic stretching techniuqes, applied to the ankle joint on balance ability. In other words, through this study, basic evidences were necessary to provide more efficient stretching techniques for improving balance ability in clinical practice by comparing the immediate effects of dynamic and static stretching of ankle joints.
As a result, although both stretching techniques did not cause statistically significant changes in the balancing ability, the dynamic stretching techniques showed significant marginal change in balancing ability. This suggests that dynamic stretching has a better effect on enhancing instantaneous balancing ability than static stretching. In other words, in the case of static stretching, it may affect tissue elongation and relaxation, but it does not significantly affect motor performance such as balance ability in a short time.
Through many studies so far, several controversies have been raised as to which is more useful between static stretching and dynamic stretching clinically. However, recent studies have shown that it would be more appropriate to use static stretching for tissue elogation and dynamic stretching to promote motor performance.
For instance, according to Behm & Chaouachi (2011), since static stretching can still increase ROM, it still plays an important role in health-related benefits associated with certain sports or activities that require a significant increase in static ROM compared to the flexibility of athletes or patients. In general, however, static stretching should not be pursued prior to strength, high speed, explosive, or reactive activities. All individuals should include static stretching in overall fitness and wellness activities for the health and functional benefits associated with increased compliance with ROM and muscle tension. Therefore, it should be planned independently of other training exercises or competitions to achieve more permanent changes in the flexibility of health or performance during separate static stretch training sessions or post-exercise cooling times. In addition, according to Yamaguchi & Ishii (2005), we observed changes in motor performance after performing dynamic stretching techniques rather than static stretching techniques.
That is, the results of this study supported that static stretching is inappropriate for immediate reaction activities (i.e. balancing ability) as described above, and it is desirable to use dynamic stretching.
Balancing abilities include static stability to maintain posture to a small degree of perturbation and dynamic stability to move in a given position without loss of balance (Ringhof & Stein, 2018). Specifically, the regulatory factors of balance ability can be divided into musculoskeletal factors and neurological factors, which refer to mechanical structures such as posture alignment and flexibility of the musculoskeletal system, and neurological factors include input sensory processing and motor output mechanisms (Yeo, Kwon & Cho, 2020). When both of these factors work effectively, they create optimized balance control, and if even one factor is injured, it leads to a loss of balance control. Therefore, as in the measurement method performed in this study, the balance ability can be measured by observing that the center of gravity is stably located on the support surface, and which would be reduced by aging or sports injury, acting as a major risk factor for falls, and posture control and cognitive function.
Finally, considering that the limitations of this study were that the number of interventions and experimental periods were short and the number of samples was small, it is judged that more accurate and reliable results could be obtained through future studies.
Ⅴ. Conclusion
In this study, in healthy adults, two experimental groups were divided randomly to find out the immediate effect of two stretching techniuqes (i.e. static and dynamic stretching) on balance ability. after observing the movement and speed of center of gravity within the base of support, as a result, there was no significant change in both groups. Although the results rejected the hypothesis that the signficant effects on balance between static and dynamic stretching would be observed, considering that a margnial significant changes was found in the dynamic stretching group, future studies will be needed to provide more accurate and objective evidences.
