Stretching and flexibility training have undergone dramatic changes in the fitness and sports training realm. Over the last ten to fifteen years more research has been published and subsequently applied to fitness and conditioning programs.
Previously, the benefits of stretching were based on perceived notions (Bracko, 2002), whereas now there is data-based evidence to support the use, or lack of use, of stretching and flexibility protocols.
As we have highlighted in our scientific rationale for stretching mini course, stretching can improve your range of motion, increase muscle flexibility, and prevent injury if done right.
Let's explore some of the research behind the benefits and relevance of stretching and flexilbility training as a whole.
Benefits of Stretching
Clark and Lucett (2015) indicate the benefits of flexibility training include: decreased chance of injury, prevention or correction of muscle imbalances, improved posture, and enhancement of joint range of motion.
Shier (2004) did a review of research literature on stretching and flexibility and found seven studies suggesting that regular stretching, not specifically stretching before exercise, improves performance on the following variables: maximal voluntary contraction, contraction velocity, eccentric and concentric contraction force, counter-movement jump height, and 50-yard dash time.
The wide variety of subjects used in the research that Shier (2004) reviewed, and the variables measured, suggests the performance benefits of regular stretching are large. Subjects in the studies included: high school students, older adults, competitive athletes, recreational athletes, and males and females.
Woods, Bishop, and Jones (2007) indicate stretching should be a long-term part of the fitness routine in order to benefit from the long-term elastic changes within the muscle, which increase range of motion potentially meaning less muscle-tendon injury.
For an interesting look into increasing hamstring flexibility with core stability exercises, look here.
An Overview of Different Types of Stretching
Research on Static Stretching
Effect of Stretch Duration
Behm and Chaouachi (2011) conducted a review of stretching research and found that when the duration of static stretching of a single muscle group is more than 90 seconds (three stretches of 30 seconds each) there is strong evidence for performance impairments immediately after the stretching. More recently, there were a number of studies showing no performance decrements caused by static stretching. The reason for this may be shorter duration stretching and lower stretching intensity. Shorter durations of stretching such as 30 seconds per muscle group, when done as part of a warm-up, may not negatively impact performance especially if used by high performance athletes or well trained fitness clients.
The duration of the stretching used in some studies does not always mimic actual practice conditions of athletes and fitness clients. When North American strength and conditioning coaches from professional sports were surveyed, they reported average stretch times for their athletes of 12 to 18 seconds for baseball, basketball, hockey and football players.
Adverse Effects of Static Stretching
Shier’s (2004) review of literature found 20 studies that showed static stretching immediately before activity decreased performance on the following tests: maximum voluntary contraction, power, jump height, jump force, and jump velocity.
Vazini Taher and Parnow (2016) investigated the performance of 22 elite college soccer players following soccer specific warm-ups using dynamic stretching, static stretching, and FIFA 11+ program. The FIFA 11+ warm-up consists of running, active stretching, and strength exercises. After the warm-up protocols the players were tested on the following tests: 1) Illinois agility test, 2) Vertical jump, 3) 30-meter sprint, and 4) knee range of motion. The results indicate vertical jump performance was significantly lower following static stretching compared to dynamic stretching. Sprint performance declined significantly following static stretching compared to FIFA 11+. Agility time was significantly faster following dynamic stretching as compared to FIFA 11+ and static stretching. Knee range of motion was significantly improved following the static stretching compared to dynamic stretching.
Static Stretching Reducing Risk of Injury
Hartig and Henderson (1999) investigated if increasing hamstring flexibility would decrease lower extremity overuse injuries in military infantry basic trainees. The control company (N 148) did normal basic training. The intervention company (N 150) did basic training and three hamstring stretching sessions to their fitness program. The stretching group increased their hamstring flexibility significantly compared to the control group.
Forty-three injuries occurred in the control group (incidence rate of 29.1%) compared to 25 injuries in the stretching group (incidence rate of 16.7%) which was significantly different. The number of lower extremity overuse injuries was significantly lower in infantry basic trainees with increased hamstring flexibility.
Pope, et al., (2000) investigated the effect of stretching and not stretching on 1538 Australian army recruits. The stretching group performed static stretching for the lower limbs during pre-exercise warm-ups while the control group did not stretch. There were 158 injuries in the stretch group and 175 in the control group, these differences were not significantly different. Therefore, the army recruits got injured whether they stretched of not. The researchers did find that fitness (20-m progressive shuttle run test score), age, and enlistment date all significantly predicted injury risk.
Small, McNaughton, and Matthews (2008) conducted a review of literature to find out if static stretching as part of a warm-up prevents injury. They reviewed research between 1990 and January 2008. Seven out of 364 studies were used for review. Four randomized clinical trials showed that stretching did not reduce injury, and one of three controlled clinical trials showed stretching did reduce injury. Three of seven studies noted significant reductions in injuries following a static stretching protocol despite nonsignificant reductions in the all-injury risk. The researchers indicate there is moderate to strong evidence that static stretching does not reduce injury. But they also say there is preliminary evidence that static stretching may reduce injuries.
Hilyer, et al., (1990) studied fire fighters and found the incidence of injury was not significantly different between a stretching group and a control group that did not stretch. However, the injuries sustained by the stretching group resulted in less lost time costs and the injuries were less severe.
Bracko (1998) discussed a fifteen-minute work-place pre-work warm-up of static and dynamic stretching with workers at a manufacturing plant. Attendance was voluntary and consisted of 30% of the workers. In the four-years the warm-up was voluntary, the injury statistics showed 86% of the workers who had minor and major injuries were not participants in the warm-up. This is not a cause and effect, but it does suggest a pre-work warm-up might reduce injuries.
Goldenhar and Stafford (2015) indicate work-related musculoskeletal injuries account for one-third of injuries in the United States construction industry. Companies have implemented stretching programs to reduce injuries despite a lack of evidence showing their effectiveness. The researchers interviewed nineteen safety professionals and surveying 133 others on-line. Fifty-six percent had implemented a stretching program. The safety professionals reporting a reduction in injuries agreed it was not due to the stretching alone. Other factors such as increased worker camaraderie, communication, and collaboration contributed to injury reduction.
NASM Integrated Flexibility Continuum
Each form of stretching creates different types of effects on the neuromuscular system. When choosing the types of stretching (and protocols) to use with clients, it is important to base exercise selection on your client’s fitness evaluations, their goals, and also when the stretching activities will take place. There are three phases of flexibility in the NASM OPT model (Clark and Lucett, 2015).
- Corrective Flexibility: This phase is designed to correct common postural dysfunctions, muscle imbalances, and joint dysfunction. It includes: SMR and static stretching (and neuromuscular stretching if trained in technique).
- Active Flexibility: This phase is designed to improve tissue extensibility. It includes SMR and active-isolated stretching (and neuromuscular stretching if trained in technique).
- Functional Flexibility: This phase is designed to improve multiplanar soft tissue extensibility and optimum neuromuscular control through a full range of motion. This includes SMR and dynamic stretching.
Behm, D.G. and Chaouachi, A. 2011. A review of the acute effects of static and dynamic stretching on performance. European Journal of Applied Physiology, 111(11), 2633-2651.
Bracko, M.R. 2002. Can stretching prior to exercise and sports improve performance and prevent injury? ACSM’s Health and Fitness Journal, 6(5), 17-22.
Bracko, M.R. 1998. Fit for duty, Canadian Occupational Safety, 36(3), 20-23.
Clark, M.A. and Lucett, S.C. (Ed.) 2015. NASM Essentials of Sports Performance. Flexibility Training for Performance Enhancement (pp. 133-166). Burlington, MA: Jones and Bartlett Learning.
Goldenhar, L.M. and Stafford, P. 2015. If you've seen one construction worksite stretch and flex program … you've seen one construction worksite stretch and flex program. Journal of Safety Research, 55, 73-79.
Hartig, D.E. and Henderson, J.M. 1999. Increasing hamstring flexibility decreases lower extremity overuse injuries in military basic trainees. American Journal of Sports Medicine, 27(2), 173-176.
Hilyer, J.C., et al,. 1990. A flexibility intervention to reduce the incidence of severity of joint binjuries among municipal firefighters. Journal of Occupational Medicine, 32(7), 631-637.
Pope, R.P., et al. 2000. A randomized trial of preexercise stretching for prevention of lower-limb injury. Medicine and Science in Sports and Exercise, 32(2), 271-277.
Shier, I. 2004. Does Stretching Improve Performance?: A Systematic and Critical Review of the Literature. Clinical Journal of Sport Medicine, 14(5), 267-273.
Small, K, McNaughton, L. & Matthews, M. 2008. A systematic review into the efficacy of static stretching as part of a warm-up for the prevention of exercise-related injury. Research in Sports Medicine, 16(3):213-231.
Woods K, Bishop P, Jones E. 2007. Warm-up and stretching in the prevention of muscular injury. Sports Medicine, 37(12):1089-1099.
Vazini Taher, A and Parnow, A. 201. Level of functional capacities following soccer-specific warm up methods among elite collegiate soccer players. Journal of Sports Medicine and Physical Fitness. Epub Jul 6.