Is chronic stretching actually beneficial?

Jackie Haffey and Matt Ballman

 

Have you ever wondered why stretching was always emphasized so heavily in gym classes growing up? Stretching is something that has been coupled with exercise all of our lives. Growing up we are taught to stretch before and after exercise in order to help prevent injury, promote recovery, and enhance your overall performance, but does it actually work? There are professional athletes out there who undergo strict training regimens that involve lots of stretching, but still manage to have career altering injuries like tearing their ACL. There are many athletes who are out there that are very talented but almost never stretch before or after a workout. On the flipside, there are many professional athletes out there that vow that stretching helps them extend their careers and improve recovery. In the NBA, yoga has become a common practice among players doing all that they can in order to help their bodies sustain their elite level of play and handle the rigors of playing in an 82 game season. Arguably the best player of all time Lebron James practices yoga regularly [6]. He even attributes it to helping him extend his career and play at a high level for as long as he has [6]. So does stretching actually help people perform better or avoid injury or is it all just a myth?

Figure1. Passive hamstring stretches

For a long time, stretching was highly recommended with little evidence to support it. Now studies are showing that acute stretching before exercise can actually be harmful as discussed in the previous blog post, “Holding Your Stretch is Holding You Back”.  So what is evidence saying about chronic stretching?When discussing effects of chronic stretching, it is referring to long term effects of consistent stretching. People normally associate this with increasing flexibility, or joint range of motion (ROM). The American College of Sports Medicine (ACSM) has recommendations for maintaining flexibility. A study was done in 2010 to support the ACSMs advice specifically for hip flexion [5]. There was a significant improvement in ROM for all stretching groups and a decrease for the control group [5]. The paper did mention its own limitation in only studying one muscle group, saying its findings should not be generalized to any muscles in the body. Another limitation was that the participants could not start a new or increase intensity of an existing exercise program during the study [5]. This may have allowed the collected data to have less noise but it may not accurately translate to real world scenarios as many athletes aim to increase workout intensity or switch up their workout programs. So with the knowledge that chronic stretching can increase ROM, how does it affect performance?

Table 1. Data from the 2007 study showing the improvements of the stretching group.

Table 2. Data from a study on D3 athletes showing no difference between stretching and control groups.

 

A study completed in 2007 had the goal of determining the effects of chronic stretching on specific exercise performances. Performed on relatively inactive people, the study lasted eight weeks long and tested whether stretching had an impact on power, strength, and endurance in the lower body by using various exercises according to each fitness category [1]. The, “stretching,” or experimental group showed significant improvement in all categories whereas the control group showed no improvements [1]. On the contrary there was a study completed on hamstring performance in female D3 athletes [4]. Six weeks long, this study found there to be no significant difference in power performance in either the stretching and control groups [4]. So maybe stretching just has an effect on sedentary individuals?

Another aspect of stretching that is renowned is its ability to decrease the body’s risk of injury. A study completed on patients with chronic neck pain had subjects undergo 6 weeks of stretching and/or global posture reeducation twice a week during that time [2]. After the study was completed it was found that both the stretching and posture reeducation groups had significant reduction in pain [2]. However, this study also lacked a control group so it is hard to tell whether the reduction in pain was at the result of a placebo effect. On the opposite end, a large scale literature search evaluated over 90 different studies trying to determine whether there was sufficient evidence that stretching does indeed reduce the risk of injury [3]. After reviewing a large amount of literature it was found that it cannot be determined whether stretching reduces the risk of injury [3]. In fact, it found it is more than likely to not have anything to do with injury risk because stretching depends on different characteristics of muscles than characteristics that rely on eccentric movement which is often the movement where non-contact injuries occur [3].

After reviewing the above literature and evaluating research that studied chronic stretching it really cannot be determined whether chronic stretching is essential in order to maintain performance and prevent injury. All of the studies observed either could not find data to support the fact that stretching indeed plays a pivotal role in exercise or the study was to limited in its structure to provide accurate results. The biggest problem was how the term, “chronic,” is defined. The longest study that we found was only 12 weeks long which can hardly represent professional athletes who have been stretching throughout their entire lives. Without longer studies it’s hard to determine anything about chronic stretching because there’s simply not enough data out there. Although stretching cannot be supported with factual scientific data it is hard to argue that it can’t hurt to stretch after exercise. With successful athletes swearing by its benefits why could it hurt to spend a little time after you exercise to stretch out? Even if it’s just for peace of mind stretching does have at least some benefit after all.

 

Questions to Consider:

In what populations is it most important to determine the effects of stretching?

Since most current studies are on the lower extremities, should studies been done on the effect of stretching the upper extremities ?

What would be your personal definition of chronic? Do you think 6 or 8 or 12 weeks studies count towards data for the effects of chronic stretching?

 

References and Further Readings:

  1. Kokkonen ’ J, Nelson AG, Eldredge C, et al. Chronic Static Stretching Improves Exercise Performance Chronic Static Stretching Improves Exercise. Performance Med Sci Sport Exerc. 2007;39(10):1825-1831. doi:10.1249/mss.0b013e3181238a2b.
  2. Aure OF, Hoel Nilsen J, Vasseljen O. Manual Therapy and Exercise Therapy in Patients With Chronic Low Back Pain. Spine (Phila Pa 1976). 2003;28(6):525-531. doi:10.1097/01.BRS.0000049921.04200.A6.
  3. Shrier I. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature. Clin J Sport Med. 1999;9(4):221-227. https://www.colorado.edu/intphys/iphy3700/shrierCritRev.pdf. Accessed May 7, 2018.
  4. Bazett-Jones DM, Gibson MH, McBride JM. Sprint and Vertical Jump Performances Are Not Affected by Six Weeks of Static Hamstring Stretching. J Strength Cond Res. 2008;22(1):25-31. doi:10.1519/JSC.0b013e31815f99a4.
  5. Sainz de Baranda P, Ayala F. Chronic Flexibility Improvement After 12 Week of Stretching Program Utilizing the ACSM Recommendations: Hamstring Flexibility. Int J Sports Med. 2010;31(6):389-396. doi:10.1055/s-0030-1249082.
  6. Toland S. The Rise of Yoga in the NBA and Other Pro Sports | SI.com. Sports Illustrated. https://www.si.com/edge/2014/06/27/rise-yoga-nba-and-other-pro-sports. Published 2014. Accessed May 7, 2018.

Muscle Stretch Shortening in Upper Extremity Explosiveness

After talking briefly about muscle stretch shortening in class, I thought this was an interesting topic and looked into some literature to better understand what is going on. I found a study that focused on upper-body explosive movements, and how load and stretch shortening cycles (SSC) affect the kinematics, kinetics, and muscle activation that occur. This was an interesting study because they looked at maximal effort bench throws, where much of the previous research focused only on lower-extremity exercises. Each subject performed an SSC throw and concentric only throws, comparing displacement, velocity, acceleration, force, power output and EMG from the pectoralis major, anterior deltoid, and triceps brachii. SSCs are usually performed before explosive movements (e.g. throwing, jumping) which lengthen the muscle preparing to contract to ensure maximal velocity is reached during the movement. When the muscle lengthens, elastic energy is stored which can then be released during the movement, however, if the time between lengthening and contracting is too long, the energy dissipates, leading to a slower contraction with less power.

As expected, the average velocity was lower for the concentric only throws when compared to the SSC throws, however, there was no difference in throw height between the two groups. Average and peak force and power output were both higher for the SSC through compared to the concentric only throw. The findings from this study agree with findings from previous studies focusing on vertical jump, showing that similar muscle kinetics are at play. Muscle kinetics are an extremely interesting area of study, and even though we only briefly discussed muscle length-tension, force-velocity, and power relationships in class, this is a huge field of study. Some groups choose to look at specific muscle groups, while others look at more complex movements that require multiple groups of muscles to be activated. This area of research has led to improvements in stretching suggestions for athletes; stretching before performing explosive movements is not actually as beneficial as we once thought. Stretching the muscle allows for elastic energy dissipation, instead of storing the energy for immediate release. However, stretching is still extremely beneficial after workouts, helping to prevent muscle soreness and excess inflammation. Additionally, there are some chronic adaptations to stretching including increasing flexibility for a wider range of motion during typical daily activities as well as athletic endeavors.

References:

  1. Newton, R. U., Murphy, A. J., Humphries, B. J., Wilson, G. J., Kraemer, W. J., & Häkkinen, K. (1997). Influence of load and stretch shortening cycle on the kinematics, kinetics and muscle activation that occurs during explosive upper-body movements. European Journal of Applied Physiology and Occupational Physiology, 75(4), 333–342. https://doi.org/10.1007/s004210050169
  2. Bosco, Carmelo, and Paavo V. Komi. (1979) Mechanical characteristics and fiber composition of human leg extensor muscles. European journal of applied physiology and occupational physiology4 (1979): 275-284.

Holding Your Stretch is Holding You Back

By: Juliana Gullotta and Laura Sturgill

If you’ve participated in any athletic event, you know that one of the first things you do is to start stretching before any activity takes place. Coaches and trainers emphasize that stretching should occur on a regular basic, and become part of an individual’s workout routine. These stretches are usually static stretches (holding a stretch for 20-30 seconds). The intent of prescribing stretching before exercise, is based on the assumption that by stretching you enhance performance, prevent injuries, and increase flexibility. However, several studies, including one from the Journal of Applied Physiology, Nutrition, and Metabolism, have shown that stretching before exercise can actually do more harm than good, and increase your risk of injury.

Results from study Conducted by the University of Nevada comparing the effects of static, ballistic, and no stretching (control) on muscle power. Asterisk signifies statistically significant.

While stretching before exercise does activate the muscles and increase blood flow to the areas as a “warm up”, it can be potentially very detrimental to an athlete’s workout. This conclusion is especially pertinent when the sport in question requires maximal force production. In a study conducted at the University of Nevada, researchers determined that leg muscles generate less force after static stretching than if they did not stretch at all. When muscles are subject to the strain of static stretching, they remain in a weakened state, thereby temporarily reducing the force that it can produce. The researchers evaluated two types of stretching, ballistic (bouncing) and static (control is no stretching). After stretching for 3 sets of 30 seconds, subjects performed a vertical jump on a force plate. Power values were compared for each of the conditions (Figure 1). From this graph it is clear to see a significant difference in the power values observed in the control group and static group. The decrease in power after stretching could inhibit a good muscle building workout. For sports that require maximum power (ex. football), static stretching should be limited before activity.

Static stretching intervals should last for no more than 60 seconds, or moderate reduction in maximal muscle performance may be observed. In a study conducted by Behm et. al. the effects of static stretching on power-speed and strength tasks were compared. One of the main components of this study involved investigating the relationship between time spent holding a stretch and subsequent performance in a physical activity. In order to perform these tests, two groups of healthy and active adults were randomly assigned, with one group holding their static stretch for less than 60 seconds and the other for a period of time greater than 60 seconds. On average there was a mean reduction of muscle performance for both test groups, but the group that held the stretch for a longer period of time experienced significantly higher reduction rates in performance. For the individuals that held the stretch for less than 60 seconds, a mean reduction of 1.1% was observed and categorized by the researchers as a small reduction in performance. However, a moderate reduction of 4.6% was noted in the population that held the stretch for longer than 60 seconds, indicating that there is a dose-response relationship between stretching and maximal muscle performance.

To investigate this relationship further, two types of physical activity were studied. Power-speed tasks were given to both groups and the results supported the notion that on average static stretching, especially when held at higher intervals, impaired muscle performance in the test subjects. While only a small mean reduction rate of 1.3% was observed for this type of exercise, this change could be extremely detrimental to an athlete’s performance where maximal speed is critical (i.e. sprinters). Power tasks were also completed, and the negative effects of static stretching on performance became more apparent. On average there was a 4.6% reduction in an individual’s maximum muscle performance, with a higher instance of 5.1% reduction when the activities were completed after a period of stretching lasting longer than 60 seconds. In another study also conducted by Behm et. al, these findings were not only supported by additional trials, but also expanded upon to look at the long term effects of stretching on overall performance. In his initial study that looked at power and speed tasks, maximal muscle performance was calculated minutes after the the stretching was complete. The second study, however, observed the prolonged effects that static stretching would have on an athlete, and concluded that even 2 hours after the last set of static stretching, instances of decreased performance existed.

The results from these studies suggest that time spent holding a stretch and subsequent muscle performance have an inverse relationship. For this reason more and more coaches and athletes are looking to implement a different approach to their warm up routine.

Straight leg march can be used as a dynamic stretch alternative to the static sit-and-reach stretch. Courtesy of the New York Times

Dynamic stretching (Figure 2) is simply the act of stretching your muscles while moving, and it is an effective method to get your blood flowing and increase your power, flexibility, and range of motion prior to working out. This type of stretching is unique in that the activities performed have the ability to target specific muscles necessary for the task at hand. In other words, different forms of dynamic stretching would be used for a sprinter and a volleyball player because each sport requires a different amount and variety of muscle activity. Dynamic stretching allows athletes to engage their bodies’ muscles in a way that static stretching cannot, thereby quickly earning its place as a replacement to static stretching in many pre-workout routines.

While the value of traditional static stretching before exercise may be an outdated concept, the benefit of increased flexibility in athletes should not be ignored. For this reason post workout stretching is recommended as a “cool down”. If necessary, short duration, lasting less than 30 seconds, low intensity static stretches could be implemented before activity to get blood flowing to muscles and reduce stiffness, but this does not offer the best possible results. The ideal warm-up routine for athletes to minimize risk of injury and maximize performance should include aerobic activity, dynamic stretching, and sport specific dynamic exercises.

Questions to consider:

How would the stretching routine you made for football players differ from that of a sprinter?

There is a lot of information about how bad form or technique during exercise can cause injury, should there be attention called to the potential adverse effects of stretching improperly?

References

Samuel, M. N., Holcomb, W. R., Guadagnoli, M. A., Rubley, M. D., & Wallmann, H. (January 01, 2008). Acute effects of static and ballistic stretching on measures of strength and power. Journal of Strength and Conditioning Research, 22, 5, 1422-8. 

Behm, D. G., Blazevich, A. J., Kay, A. D., & McHugh, M. (January 01, 2016). Acute effects of muscle stretching on physical performance, range of motion, and injury incidence in healthy active individuals: a systematic review. Applied Physiology, Nutrition, and Metabolism =, 41, 1, 1-11.

Shrier, I. (October 01, 1999). Stretching Before Exercise Does Not Reduce the Risk of Local Muscle Injury. Clinical Journal of Sport Medicine, 9, 4, 221-227.

Behm, D. G., & Chaouachi, A. (November 01, 2011). A review of the acute effects of static and dynamic stretching on performance. European Journal of Applied Physiology, 111, 11, 2633-2651.

Shrier, I. (January 01, 2000). Stretching before exercise: an evidence based approach. British Journal of Sports Medicine, 34, 5, 324-325.

Herbert, R. D., & Gabriel, M. (January 01, 2002). Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. Bmj (clinical Research Ed.), 325, 7362.)

Reynolds, Gretchen. (2008) Stretching: The Truth. The New York Times. Retrieved from: http://www.nytimes.com/2008/11/02/sports/playmagazine/112pewarm.html

Reynolds, Gretchen. (2016) The Right Way to Stretch. The New York Times. Retrieved from: https://well.blogs.nytimes.com/2016/01/21/stretching-back-to-the-past/

Nah Coach, I don’t have to stretch.

Ever wondered if those pre- and post- workout sessions really make a difference in your daily exercise regimen? It is commonly believed that stretching prior to and following a workout will decrease the likelihood of injury, minimize post workout pain, and increase performance. However, other athletes and trainers believe that stretching has no impact on these factors and can even decrease strength and performance. But what are the facts?

Figure 1. Examples of active and passive/static and dynamic stretching.

There are several subgroups of stretching but I will focus on performance results with regards to the two most well researched types: static versus dynamic. Each stretch can be done actively or passively, where active stretching is when you contract the muscle in opposition to the one you want to stretch and passive uses an external force such as a strap, the force of your body weight, or gravity. Each type of stretching, shown above, has been shown to impact exercise in different ways. Let’s start with the most frequently used type, static stretching, where a person slowly moves muscles until they reach the brink of pain and hold that position for 20-30 seconds.

Static stretching has been compared to continuously stretching a rubber band. Immediately after stretching the rubber band, the band remains limp as it contracts slowly back into its original form, similarly to the behavior of a muscle. It seems unrealistic to expect a maximum amount of contraction and force immediately after stretching your muscle. In more physiological terms, the loss of muscular stiffness caused by static stretching results in an increase in length of sarcomeres in each muscle fiber, decreases contact between actin and myosin, and therefore decreases the force produced (Shrier, 2004; Kokhonen et al., 2004).

Figure 2. Actin and myosin movement in relaxed muscle versus contracted muscle. The less contact between actin and myosin, the less force produced.

One study by Fletcher and Jones (2004) on 97 male rugby union players showed a significant decrease in sprint times for the passive static stretch group. This could be due the mechanical impact of stretching on the muscle, kinematic differences, or neural inhibition which decreases the neural drive to muscle. Dynamic stretching focuses on moving through a range of motion repeatedly and mimics motion that will occur during exercise. Fletcher and Jones’ (2004) study showed more beneficial performance results from active dynamic stretching prior to sprinting though. The active dynamic stretch group of rugby players improved their sprint times significantly.

These results could be explained by information in a systematic review of studies on stretching and exercise by McGowan et al. (2015). This review showed that dynamic stretching increases the temperature of the muscle more than static stretching. This increase in temperature activated an increase in muscle metabolism, elevated oxygen uptake, and increased the power output of the muscle. Another study by Gray et al. (2008) showed a correlation between increased muscle temperature and faster ATP turnover, caused by an elevated rate of creatinine phosphate utilization and H+ accumulation. The elevated muscle temperature also resulted in short term (~2 minute) increase in anaerobic glycolysis and muscle glycogenolysis. These physiological responses, in theory, would result in greater power production during sprint and sustained high-intensity exercise, however high quality research results on this topic are limited.

Several literature reviews regarding this topic exist, but compiling results from hundreds of varying studies makes it difficult to normalize the results. Several reviews analyzed results that were not statistically significant, skewing the review results. By looking at the methods researchers used to gather and compile data and at the sources they cited, I was able to identify the sources where results were significant and relevant. The review also covered studies on a span of sports from swimming, to sprinting, to jumping, all which are impacted very differently by stretching, which makes the conclusions for these reviews far reaching statements. When more studies are done within each of these sports, reviews that group together specific events and exercises will provide more beneficial results.

When looking at the impact of stretching on pain, several papers used self-reported ratings of pain to measure differences. In those studies the results did not show a significant difference between ratings from groups that stretched and controls. Self-reported measurements of pain contain bias which makes them difficult to compare between groups of people. Some papers overcame bias by observing differences in delayed muscle soreness by measuring creatine kinase levels, a commonly used marker for muscle damage. One experiment by Buroker and Schwane (1989) showed no significant difference in creatine kinase levels from stretching post-exercise. Very few studies are done solely to measure the effect of post-exercise stretching on soreness and risk of injury so it is difficult to differentiate these results from the pre-exercise stretching.

Keeping these biases and knowledge gaps in mind when considering the results of these papers, it is plausible that for the majority of exercises, dynamic stretching can positively impact your performance. This is largely due to the fact that it increases the core body temperature and targets activity in specific muscles that will be used instead of just stretching them. Static stretches prior to a workout seem to have no impact or a negative impact on performance since the muscle needs time to recover and regain stiffness before use. Personally, this would convince me to do some dynamic stretches before my next run rather than static stretches. While it differs from sport to sport, dynamic stretching appears to be the ideal pre-exercise stretch to optimize performance.

Recommended Further Reading:

1. Blahnik, Jay. Full-Body Flexibility, Second Edition. Available at: http://www.humankinetics.com/excerpts/excerpts/types-of-stretches

2. Sifferlin, Alexandra. Why Stretching May Not Help Before Exercise. (April 08, 2013) Available from: http://healthland.time.com/2013/04/08/why-stretching-may-not-help-before-exercise/

3. Shrier, Ian. Sports Med (2004) 14:267-273. Available from: http://www.elitetrack.com/article_files/stretchingreview.pdf

4. Kokkonen,  J.,  Nelson,  Α.  G.,  Cornwell,  Α.  (1998). Research Quarterly for Exercise and Sport. 69 (4): 411-415. Available from: https://www.ncbi.nlm.nih.gov/pubmed/9864760

5. Fletcher, IM, Jones, B. J Strength and Condition Research. (2004) 18(4), 885-888. Available at: http://staps.nantes.free.fr/L3/entrainement/etirements/THE%20EFFECT%20OF%20DIFFERENT%20WARM-UP%20STRETCH.pdf

6. McGowan, C.J., Pyne, D.B., Thompson, K.G. et al. Sports Med (2015) 45: 1523. Available at: https://link-springer-com.udel.idm.oclc.org/article/10.1007%2Fs40279-015-0376-x

7. Gray, SR, Soderlund, K, Ferguson, RA. J Sports Sci. (2008) 26(7):701:7. Available at: https://www-ncbi-nlm-nih-gov.udel.idm.oclc.org/pubmed/18409101?dopt=Abstract

8. Buroker, KC, Schwane, JA. The Physician and Sportsmedicine (1989) 17(6): 65-83. Available from: http://www.tandfonline.com/doi/citedby/10.1080/00913847.1989.11709806?scroll=top&needAccess=true