17 minute read
The effect static and dynamic stretching have on hamstring flexibility
The effect static and dynamic stretching have on hamstring flexibility
Madeline Irvin
Leeton High School
Abstract
High flexibility levels have been found to promote performance and prevent injury. Since hamstring injury is common amongst athletes it is important to maintain hamstring flexibility. This study compared static and dynamic stretching types to determine which method has the most positive effect on hamstring flexibility. 60 participants were randomly split into 3 groups: static stretching, dynamic stretching and control group. The two stretching groups received either a static or dynamic stretch to complete 3 times per week over a 6-week program. The initial and final hamstring flexibility distance was tested using a sit-and-reach box. The average improvement distance of each group after 6 weeks was compared to the improvement results of the other groups to determine which stretching type was the most effective. The p-value of 0.378007939 was much greater than the confidence level of 0.05, meaning the null hypothesis was accepted. However, this also meant the data had no statistical significance therefore there was no difference in the change in sit and reach distance between participants in the different stretching groups. Although statistically no clear outcome was determined, the average improvement distance of the dynamic stretching groups was further than that of the static, supporting the research hypothesis.
Literature review
Research suggests that hamstrings with higher flexibility have a reduced chance of injury. A common cause of muscle injury is muscle overload. This occurs when a muscle is stretched beyond its range of movement. An individual with tight hamstrings may be at risk of a hamstring injury as they have a reduced range of motion (Hamstring Muscle InjuriesOrthoInfo - AAOS, n.d.). Maintaining flexibility allows the muscles to have a good range of movement and decreases the risk of injury. Without stretching, muscles become short and tight, which can increase the susceptibility to strain and muscle damage (Stretching: Focus on Flexibility, 2022). Other risk factors for hamstring injuries include previous hamstring injuries, muscle imbalance and tired, weak muscles. Muscles that are tired and weak don’t have great elasticity meaning they are at higher risk of injury (Hamstring Injury - Symptoms and CausesMayo Clinic, 2022). Hence why it is important to maintain flexibility to reduce the chances of a hamstring injury. Regular stretching of the hamstring keeps muscles loose and strong. The primary goal of stretching a muscle is to improve the range of motion. This improved range of motion is due to the increased length and flexibility of the muscle. Hamstring strains are one of the most common injuries that occur in sports. For example, hamstring injuries make up 15% of total injuries in Australian Rules Football (Rachel, 2021). Hence, enhancing the flexibility of the hamstring will allow easier movement when completing exercises such as running, walking and kicking, reducing the chance of an injury occurring (O’Sullivan, 2009).
The hamstring is made up of three muscles that are located in the back of the upper leg. The tendons of the hamstring attach the muscle to the pelvis, knee and lower leg. The hamstring muscles are very important when it comes to running, walking and any movement that requires flexion of the knee joint and extension of the hip (Hamstring Muscles: Location, Anatomy & Function, n.d.).
Two common types of stretching are static and dynamic. Static stretching is when a muscle is stretched to a length that is uncomfortable, not painful, and held for between 30 and 60 seconds. Whereas dynamic stretching is when an athlete performs a continuous movement that takes their joints through their range of movement to produce a stretch (Jackson, n.d.). Stretching is most beneficial if completed 2-3 times per week. Maintaining a consistent and regular stretching routine will help avoid reversibility of flexibility and range of movement (Therapy, 2021). Meroni et al., 2010 investigated the impacts of active and passive stretching techniques on hamstring flexibility. During this comparison, the study found that active stretching produced a greater gain in hamstring flexibility and was required less frequently to produce effects on hamstring flexibility.
Sit and reach box
The sit and reach box testing method will be used in this investigation as it measures hamstring and lower back flexibility. However, the stretches included in the experiment focus on improving hamstring extensibility rather than stretching the lower back to gain hamstring-specific and accurate results from the test. During the sit and reach test the participant puts their feet flat against the box and their legs stretched out. Knees should be locked and flat against the floor. With hands overlapping and palms down, the subject must reach forward along the measuring line as far as possible pushing the slider without any jerky movements or bounces. Where the slider stops is the flexibility of that participant’s hamstrings (Sit And Reach Test, n.d.).
This project was chosen to further increase understanding of the effects stretching can have on hamstring flexibility and the positive outcomes that can come from stretching. This research will further explore specific types of stretching, dynamic and static, and which is the most efficient way to improve hamstring flexibility.
Scientific research question
What effect does static and dynamic hamstring stretching have on hamstring flexibility within a population?
Scientific hypothesis
A population who engage in regular dynamic hamstring stretches will improve their sit and reach testing results to a greater extent than those who complete regular static hamstring stretches.
Methodology
Gathering volunteers
A survey was prepared to gain information about the participants in relation to their age, gender, activity levels and injury history.
The 60 participating volunteers, 30 females and 30 males, had to pass the inclusion criteria. They must:
a. be between the ages of 16-40
b. have no acute or severe back pain
c. have had no acute hamstring tears in the past week
All volunteers completed the electronic pretesting survey (Appendix 1) prior to having their hamstring flexibility tested. The data was collected directly into a spreadsheet.
The pre-testing survey outlined how the data would be used so that the participants understood what the experiment involved. This survey required them to answer questions about their health to ensure they were fit to participate in the experiment. Due to this, 2 participants were denied participation because of the health risks associated. Furthermore, each volunteer was provided with the same information regarding how to safely complete their stretching program to avoid injury.
Initial Testing
Before completing the hamstring test, each participant completed 1min on the bike or low-intensity step-ups to warm up their muscles and avoid injury whilst being tested.
Immediately after completing the warm-up, the participants completed their hamstring testing.
Their results were recorded directly into a spreadsheet under initial sit and reach distance (cm).
The following steps were followed by the subjects whilst being tested:
a. Remove shoes and sit flat on the floor.
b. Place feet against the BaselineSit and Reach box.
c. Ensure legs are stretched and remain flat against the floor.
d. Push the slider as far as possible using both hands, one on top of the other (As seen in Figure 1).
o There should be no bouncing to increase the distance
o Where the slider on the sit and reach box ends up is the furthest distance the participant reached.
Stretching program
The 60 participants were randomly assigned into 3 groups of 10 males and 10 females.
Group 1 completed the 6-week static stretching program. The stretch they completed was the standing hamstring stretch (figure 2).
Group 2 completed the 6-week dynamic stretching program. The stretch they completed was the single-leg deadlift stretch (figure 3).
Each group was provided with a QR code that linked to a demonstration video and explanation to ensure they completed the stretches with the correct technique. The stretch is to be completed 3 times a week for 6 weeks.
Group 3 was the control group that continued their everyday lives without completing specific stretches.
Figure 2: Video of static hamstring stretch (MyChartScottish Rite for Children, 2017)
https://www.youtube.com/watch?v=gYsasEGWiM&t=4s
Figure 3: Video of dynamic hamstring stretch (3v, 2012)
https://www.youtube.com/watch?v=HtHxnW mMgzM&t=6s
Final Testing
After 6 weeks all participants were gathered at the same location and steps 3-5 were repeated, ensuring each participant completed the same warm-up. The results were recorded into a spreadsheet under ‘final sit and reach distance (cm)’.
Statistics analysis
Microsoft Excel was used for the collection of the initial and the final measure taken 6 weeks apart. Using the data analysis add-on an ANOVA: single-factor test was completed to determine if there was a statistical significance between the means of the 3 groups.
Results
Statistical Analysis
ANOVA: single factor
Alpha Significance Level = 0.05
H0- There is no difference in the change in sit and reach distance between participants in the different stretching groups.
Ha- There is a difference in the change in sit and reach distance between participants in the different stretching groups.
An ANOVA Single factor test was used to determine if there was a significant difference between the means of the different stretching groups’ improvement results. This is a suitable test as there are more than two stretching groups. .
Discussion
This study aimed to determine if there was a relationship between the type of hamstring stretches and the flexibility of the hamstring. Results revealed that both the static and dynamic stretching types lead to an improvement in flexibility levels when compared to the control group (Refer to Figure 4, Figure 5 and Figure 6). The average improvement results of the dynamic stretching group supported the scientific hypothesis ‘A population who engage in regular dynamic hamstring stretches will improve their sit and reach testing results to a greater extent than those who complete regular static hamstring stretches.’ However, statistical analysis showed that there is no statistical significance in the results.
After completing a single-factor ANOVA test, the results revealed that the calculated P value of 0.378007939 was much greater than the confidence level of 0.05 needed to indicate a significant difference. Hence the null hypothesis, ‘there is no difference in the change in sit and reach distance between participants’, is accepted, supporting the statement that there is no statistical significance between the improvement values of each stretching group’s results, rather the difference may be the result of natural variation within the population. The results from the pre-testing survey (Appendix 2) and the weekly check-in surveys (Appendix 3) provided information on uncontrollable external factors such as physical fitness and injury that may have affected the participant’s sit-and-reach results. Since the data collected had no statistical significance these surveys supported the outcome, providing evidence for external impacts. Furthermore, the F value is smaller than the F critical value supporting the acceptance of the null hypothesis. Table 4 indicates that the variance of the static stretching group is 10.2216374 and the variance of the control stretching group is 7.71736842. These large numbers suggest that there is an outlier that could be affecting the accuracy of the results. Alternatively, the variation could be caused by the disparity between the participant’s age, height, gender, and physical activity levels. Whereas the variance of the dynamic stretching group is 5.27355263. Since this number is smaller compared to the other two groups it suggests that the data set is close in spread. This variance can be clearly seen by examining Figure 7. This result makes sense as the change in sit and reach results, displayed in Figure 7, show a variety of improvement distances. Since this investigation relied heavily on trust in each participant, the reliability may have been affected by the consistency of participants undertaking the exercise regime (shown in Appendix 3).
Multiple studies have been conducted that investigate the effect stretching has on hamstring flexibility, with many different approaches. The results from this experiment align with the credible study completed by Meroni et al., 2010. Both studies’ results suggest that active stretching (dynamic) was more efficient at improving hamstring flexibility. However, the study completed by Meroni et al., 2010 utilised the active knee extension range of motion (AKER) test to determine the flexibility of the hamstring rather than the sit-and-reach test. Both studies implement a parallel design randomised control trial method of experiment. This occurs when participants are randomly split into 2 or more equal groups, where each group receives their individual trial, which is then compared at the conclusion of the investigation period. This method of investigation provides an inadequate evaluation when the sample size being studied is small. Many naturally occurring variables that are difficult to control lead to implications during the investigation. Different starting fitness levels of participants along with varying heights and weights all impacted the results. This was due to the correlation between relative sitting height and sir-and-reach results. To fix this problem a modified sit-and-reach testing box should be used as it controls the variations in arm, leg, and torso length, which the standard test used in this study is not able to do. It adjusts the measurements of the sit-andreach test depending on the length of the participant’s arms, legs, and torso.
The reliability of an investigation is determined by comparing the proximity of the measurements across repetitions. Hence, the reliability of this study is low as there is a high variance, as shown in Table 4, meaning a high spread of results. Furthermore, since the entire experiment was not able to be repeated for a further 6 weeks these results cannot be compared with other findings. Similarly, to establish validity within an experiment, only one independent variable must be changed to determine its effect on the dependent variable. In this study, the dependent variable was hamstring flexibility, and the independent variable was the type of stretching. However, there were multiple factors including gender, height, weight, exercise levels and age that impacted the improvement of the sit-andreach results, which reduced the validity of the findings. The Baseline sit-and-reach box used throughout the experiment is a valid test that measures the extensibility of the hamstrings and lower back. For the focus to remain on hamstring improvement when using the sit-and-reach box, the stretches included in the 6 weeks stretching program must target the hamstring area specifically. Another implication faced was the inconsistency of stretching that occurred within the two stretching groups. Not all participants regularly completed their stretching program which had an impact on the final improvement results of each stretching group, which also affected their variances. However, this study had multiple strengths that contributed positively to the effectiveness of the experiment. This investigation involved simple testing methods with easy-to-follow instructions to complete the 6-week stretching program. The simplicity of the experiment and instructions increases the likelihood the participants could follow it and complete their stretching program effectively. Only altering one variable increases the control over the experiment, reducing the chance of an error occurring.
To find a valid and reliable result it may be necessary to reduce the number of variables that weren’t able to be controlled. Focusing specifically on a certain age, gender or height may increase the statistical significance of the data. The results from this experiment provide the opportunity for various other studies to be completed. Future studies may involve focusing on gender or a smaller age range to determine whether these factors directly affect hamstring extensibility. This may answer questions about the relationship between hamstring flexibility and injury.
This investigation attempted to determine which type of hamstring stretch improved hamstring flexibility to the greatest extent. A clear answer was not obtained so more repetitions of this experiment may provide an obvious pattern and reliable results. To verify why certain stretches improve hamstring flexibility within a certain duration; the period of the stretching program and stretch types, such as Proprioceptive Neuromuscular Facilitation and resistance stretching, could be changed.
Conclusion
This study was conducted to determine which type of stretching, either static or dynamic, improved hamstring flexibility to the greatest extent. It was hypothesised that ‘A population who engage in regular dynamic hamstring stretches will improve their sit and reach testing results to a greater extent than those who complete regular static hamstring stretches.’ The dynamic stretching results supported this hypothesis as on average the 6-week dynamic stretching program saw the greatest improvement in sit-and-reach distance compared to the other 2 groups. However, due to the impact of uncontrollable external factors such as age, height, gender and physical activity level, the validity of the investigation was impacted.
An ANOVA single-factor test was performed which demonstrated that the data had no statistical significance. The p-value was greater than the confidence level of 0.05 hence the null hypothesis was accepted. These results could have occurred due to outliers and inconsistent data indicating the effect of external factors. Figure 7 clearly shows the vast variations in improvement results amongst the 3 groups caused by uncontrollable factors.
This study shows that regular hamstring stretching increases flexibility and would therefore be beneficial for reducing the risk of hamstring injury. However, further research may include increasing the duration of the stretching program, narrowing the range of participants in order to reduce uncontrolled variables, or investigating other stretching types. Adjusting these factors would strengthen the outcome of the investigation.
Acknowledgement
I would like to acknowledge the Physiotherapist, Sally Hill, from Leeton Physiotherapy Centre who assisted me in the development of my investigation by providing first-hand information regarding the hamstring function. She also gave me access to static and dynamic stretches that would suit my study’s purpose. I would also like to acknowledge the Leeton-Whitton Football Netball Club for allowing me to use the club gym to complete sit-and-reach testing. They also supported me in gaining my data by allowing me to test participants during training time. Finally, I would also like to thank Jane O’Garey from Rise and Shine Fitness for allowing me to utilise the facilities at her gym to conduct hamstring warm-ups and testing.
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Appendix 1: Pre-testing survey
