Donny, Zach, and I share our thoughts and sentiments about stretching on our first episode of the Active Ingredients Podcast after our literature round up. We think the jury is still out about what happens with stretching, but it appears that researchers are leaning towards a modification of our sensory perception more than a physical change in regards to increasing range of motion. Stretching is a variable tool with pros and cons as to what it can do for injury prevention, performance, and mobility. How you are stretching should probably be matched to your history of injury, goals, and demands of your sport or exercise.
That said, my opinion is that there are some general rules that can be gleaned from all of this. If you plan to participate in sport and exercise it is probably best to perform Active/Dynamic stretches (like I talk about in my Squat Guide) beforehand to increase flexibility and warm-up without the potential loss of performance. If you have known areas of poor mobility, PNF (Contract-Relax/Contract-Relax-Antagonist-Contract) and Static type stretching can be used on your days off to improve it, and stretches should be performed for 5 or more minutes per muscle group you are targeting. The more consistent you are with your program, the better results you will probably get. I believe Yoga is one readily available alternative that can help. One home program I’ve encountered that I’ve liked was ROMWOD. While it’s geared toward CrossFit athletes, I like how it makes you hold stretches for several minutes.
We sifted through over three dozen articles to help us answer questions about stretching. Below are the articles we felt were most helpful in answering our questions about stretching for this episode. We included our short summaries below for you to read. Always be sure to check with your health care professional or trainer if you are uncertain what you should be doing. If you’re looking for more knowledge on Kirkland chiropractic care, do not hesitate to contact me.
Stretching Research Article Summaries
Mayorga-Vega D, Merino-Marban R, Manzano-Lagunas J, Blanco H, Viciana J. Effects of a Stretching Development and Maintenance Program on Hamstring Extensibility in Schoolchildren: A Cluster-Randomized Controlled Trial. Journal Of Sports Science & Medicine [serial online]. March 2016;15(1):65-74.
The Take Away: This study demonstrated that with kids with less flexibility in the hamstrings, a moderate stretching program of 4 minutes 2x/wk for 9 wks was effective at improving flexibility where gains can be maintained with a subsequent 1 minute 2x/wk. Kids with good flexibility had less to gain. In other words, it takes a lot of work to get to where you want to be for flexibility, but it’s less work to maintain once you are there.
Bing Y, Hui L, William E. G. Mechanism of hamstring muscle strain injury in sprinting. Journal Of Sport And Health Science, Vol 6, Iss 2, Pp 130-132 (2017) [serial online]. 2017;(2):130.
The Take Away: The authors cite several research papers to explain the mechanism of strain injuries and conclude that excessive muscle strain while muscles are under eccentric contraction (lengthening under load) is the mechanism for injuring. In the hamstrings this can happen in the late swing phase of running and late stance before take off.
Xianglin W, Feng Q, William E. G, Hui L, Bing Y. Relationships among hamstring muscle optimal length and hamstring flexibility and strength. Journal Of Sport And Health Science, Vol 6, Iss 3, Pp 275-282 (2017) [serial online]. 2017;(3):275.
The Take Away: The authors define Hamstring Optimal Length is defined as the length at which the hamstring generates peak torque about the hip joint. This study suggests that a hamstring that is more flexible produces this peak torque about the hip joint at longer lengths (higher joint angle), which increases the threshold at which the muscle begins to mechanically strain, possibly leading to less injury.
Hsuan S, Nai-Jen C, Wen-Lan W, Lan-Yuen G, I-Hua C. Acute Effects of Foam Rolling, Static Stretching, and Dynamic Stretching During Warm-ups on Muscular Flexibility and Strength in Young Adults. Journal Of Sport Rehabilitation [serial online]. November 2017;26(6):469-477.
The Take Away: The authors find that foam rolling, static stretching, and dynamic stretching are good at improving flexibility of quadriceps and hamstrings with a slight edge for the foam roller. Foam rolling doesn't appear to change strength for better or worse. Increased in knee extension peak torque (work of quadriceps) is found to improve with dynamic stretching. Authors are also unsure if the increase in flexibility comes from mechanical changes to tissue to changes to the sensation of the stretch endpoint.
Weppler C, Magnusson S. Increasing muscle extensibility: a matter of increasing length or modifying sensation?. Physical Therapy [serial online]. March 2010;90(3):438-449.
The Take Away: The authors investigate that muscle stretching theories of viscoelastic deformation, plastic deformation, and neuromuscular relaxation have not been well supported by prior research as effects are transient, or no changes could be observed on torque/joint angle curves that would suggest muscles have lengthened (a longer muscle allows more range of motion before resistance starts to increase as it approaches end range). The end range of prior studies are often dictated by subject’s perception of pain, so by deduction, the only current explanation that can explain the increased range of motion is an increase in pain tolerance which has been purported by other studies. However, most studies have not been designed to investigate the effects of higher dosage (stretches beyond 2-3 minutes, stretching programs beyond 8 weeks) on the torque/joint angle curves.
McHugh M, Cosgrave C. To stretch or not to stretch: the role of stretching in injury prevention and performance. Scandinavian Journal Of Medicine & Science In Sports [serial online]. April 2010;20(2):169-181
The Take Away: In terms of increasing flexibility, the authors investigate dosage from different studies and find that the effects of passive stretching are marked when stretching reaches 5 minutes per muscle. However, the effects wear off after a short time. Outside of ballet dancers, they question how much time is available for pre-participation stretching of multiple muscle groups with other athletes and suggest that ways to combine stretches can help reduce some of this time. In regards to performance, the authors find that passive stretching to a relaxed muscle can produce small loss of strength afterwards, surprisingly even on the opposite limb that was not stretched. Small losses in performance measures such as the vertical jump (3-4%) and sprint (0-2%) have also been observed. They find no stretch-induced strength loss with dynamic stretching, at least for eccentric contractions. Pre-participation stretching in addition to warming up will unlikely to decrease injury risk in activities where overuse injuries are dominant, but stretching interventions studied so far may not have been good enough. In light of the existing research, the authors find it reasonable to recommend pre-participation stretching to muscle groups known to be at risk for injury for a particular sport and to apply 4-5 reps of 60 second stretches to pain tolerance on both sides and to avoid lingering stretch-induced strength loss, perform some dynamic sub-maximal drills.
Behm D, Blazevich A, Kay A, McHugh M. 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 [serial online]. 2016:1.
The Take Away: The authors find that Static and PNF stretching causes small single digit percentage decreases in various performance measures immediately after stretching which may affect elite athletes if play time is in close proximity to the stretching. The decreases in strength and performance appear to increase as the length of time spent performing the stretches increases. Because muscle strains are implicated at longer muscle lengths (as we’ve seen in other articles), Static and PNF stretching may be protective of those, but studies do not seem to suggest them to be protective of overuse injuries. They might be protective in preventing acute injuries with running, sprinting, and activities with repetitive contractions. Dynamic stretching does not appear to decrease performance and may even slightly improve performance if performed for more than 2 minutes and at a faster frequency. All forms of stretching have been shown to increase joint range of motion.
Medeiros D, Cini A, Sbruzzi G, Lima C. Influence of static stretching on hamstring flexibility in healthy young adults: Systematic review and meta-analysis. Physiotherapy Theory & Practice [serial online]. August 2016;32(6):438-445.
The Take Away: The authors round up several prior studies to crunch the numbers together and determine that static stretching is effective in increasing hamstring flexibility in healthy young adults. But due to differences in how it was studied between studies, they claim it is not possible to determine optimal stretching training parameters.
KAY A, RICHMOND D, TALBOT C, MINA M, BAROSS A, BLAZEVICH A. Stretching of Active Muscle Elicits Chronic Changes in Multiple Strain Risk Factors. Medicine & Science In Sports & Exercise [serial online]. July 2016;48(7):1388-1396.
The Take Away: The authors cite evidence of eccentric exercise being protective of strain injuries but the increased muscle stiffness from training may also affect strain risk. They investigate an eccentric stretching program twice a week for 6 weeks to increase ankle mobility in subjects. The procedure involved subjects maximally plantarflexing their ankle against a dynamometer that steadily pushed their ankle into dorsiflexion. The authors found at the end of the study that significant improvements in ankle range of motion was achieved compared to passive stretching or other eccentric training programs. They also observed improved stretch tolerance, improved energy storage, and increased strength were observed after the study. All these factors may be protective against strain injuries.
Manickam R, Shailesh M, Vyas A. A Study to Compare the Efficacy between Active Self Stretching and Self PNF Stretching on Hamstring Flexibility among Normal Individuals. Indian Journal Of Physiotherapy & Occupational Therapy [serial online]. April 2017;11(2):92-97.
The Take Away: The author performed a study comparing the difference between a self Static stretching and PNF stretching program on hamstring mobility using two groups over the course of 6 weeks, once per day for 10-15 minutes. The procedures involved the subjects laying on their back with the heel of one leg propped against the doorframe with the knee extended and other leg and hip flat against the ground. One group was instructed to simply move the buttock as close to the doorframe and hold for 30 seconds and relax and repeat 5 times. The other group had the same set up, but was asked to press the heel into the door frame for a count of 5, then lifting the leg away from the frame. This was repeated 5 times. It was found that the self PNF stretching was effective at increasing flexibility in a back saver sit and reach test and 90/90 knee extension test whereas self Static stretching only improved the back saver sit and reach test.
Medeiros D, Martini T. Chronic effect of different types of stretching on ankle dorsiflexion range of motion: Systematic review and meta-analysis. Foot [serial online]. March 2018;34:28-35.
The Take Away: The current review demonstrated that chronic Static and PNF stretching is effective to increase ankle dorsiflexion. Static stretching was the most common approach by the studies because it is easy to self-perform and shows good results. However, PNF stretching (especially self stretching protocols) should not be disregarded in a flexibility training routine. Ballistic stretching was not shown to be helpful.
WOOTAEK L, HYUNJU P. No significant correlation between the intensity of static stretching and subject's perception of pain. Journal Of Physical Therapy Science [serial online]. October 2017;29(10):1856-1859.
The Take Away: The purpose of this study was to determine whether the intensity of static stretching measured quantitatively related to subjects perception of pain. No significant correlation was found between the intensity of stretching and the VAS score representing the subjects pain scaled on one’s perception. Therefore, subject’s response cannot guarantee a consistent application of intensity.
Mohr A, Long B, Goad C. Effect of Foam Rolling and Static Stretching on Passive Hip-Flexion Range of Motion. JOURNAL OF SPORT REHABILITATION [serial online]. 2014:296.
The Take Away: To determine if foam rolling before static stretching produces a significant change in passive hip flexion ROM. There was a significant change in subjects Passive Hip Flexion ROM regardless of treatment. Subjects that received foam rolling and static stretching had a greater improvement in passive hip flexion ROM.
Ruan M, Zhang Q, Wu X. Acute Effects of Static Stretching of Hamstring on Performance and Anterior Cruciate Ligament Injury Risk During Stop-Jump and Cutting Tasks in Female Athletes. Journal Of Strength And Conditioning Research [serial online]. May 2017;31(5):1241-1250.
The Take Away: The authors wanted to look at the influence of static stretching of the hamstring muscle group and whether performance was affected. Static stretching did increase some of the performance metrics it did also increase the potential ACL injury risks because it reduced the strength and stiffness of the muscle thereby decreasing the overall stability of the knee joint itself.
Payla M, Gill M, Singal S, Shah N. A Comparison of the Immediate and Lasting Effects between Passive Stretch and Muscle Energy Technique on Hamstring Muscle Extensibility. Indian Journal Of Physiotherapy & Occupational Therapy [serial online]. January 2018;12(1):24-29.
The Take Away: This study looked at two types of stretching techniques and their effect on hamstring flexibility and extensibility. Hamstring extensibility is valuable for both the sporting and general population as is mitigates the negative effects of hamstring tightness. The muscle energy technique was superior to passive stretching because there seemed to be less associated stretching pain which makes the technique more comfortable.
Dong Ho K, Young Uk R. Applying proprioceptive neuromuscular facilitation stretching: optimal contraction intensity to attain the maximum increase in range of motion in young males. Journal Of Physical Therapy Science [serial online]. July 2015;27(7):2129-2132.
The Take Away: This study looked at PNF stretching and how intensity of the contraction changes the efficacy of the stretch as a whole. It found that it is not necessary to apply maximal intensity of muscle contraction while performing PNF stretching, in fact the biggest gains were found at a moderate isometric contraction.
THANDA A, TSUGUMI K, HEONSOO H, HITOSHI M. Comparison of immediate effects between two medical stretching techniques on Hamstrings flexibility. Journal Of Physical Therapy Science [serial online]. September 2017;29(9):1518-1521.
The Take Away: The authors of this study wanted to study the immediate effects of new medical stretching and conventional medical stretching on the flexibility of the hamstring muscle group. The biggest difference in the two techniques is not what is happening on the limb that is being stretched but on the opposite leg. In new medical stretching, the opposite limb is placed in an open position (flexion, abduction, and external rotation) which is contrary to conventional medical stretching in which the opposite limb is closed (flexion, adduction, and neutral rotation of the hip joint and extension of the knee joint). Both medical stretching techniques had an immediate effect on hamstring flexibility but the new medical technique was MORE effective.
SATOSHI K, SHIGEYUKI S, KAZUAKI Y, et al. ACUTE EFFECTS OF THE DIFFERENT INTENSITY OF STATIC STRETCHING ON FLEXIBILITY AND ISOMETRIC MUSCLE FORCE. Journal Of Strength & Conditioning Research (Lippincott Williams & Wilkins) [serial online]. December 2017;31(12):3403-3410.
Behara B, Jacobson B. Acute Effects of Deep Tissue Foam Rolling and Dynamic Stretching on Muscular Strength, Power, and Flexibility in Division I Linemen. Journal Of Strength And Conditioning Research [serial online]. April 2017;31(4):888-892.
The Take Away: The authors of this study wanted to examine whether or not the intensity of the stretch had any effect on flexibility or muscle force. They used static passive torque, range of motion, passive joint stiffness, passive torque at onset of pain, and isometric muscle force as the markers for lower limb function and flexibility. While all intensities of stretching showed some improvements in these tests, it was found that when the stretches were performed at maximum or just above tolerable stretching pain, range of motion showed the largest increase while muscles stiffness showed the biggest decrease. This indicates that stretches should be held to their maximum threshold to see results.