Does Flexibility Affect Sport Injury and Performance?

Flexibility is defined as the range of motion around a specific joint or a series of joints and is either static or dynamic (American College of Sports Medicine, 2000). Static flexibility refers to the degree to which a joint can be passively moved to the end points in the range of motion. Measurements are obtained when an individual is relaxed and stretches a muscle tendon unit. Static hamstring and lower-back flexibility would determine if you could touch your toes. The sit-and-reach test measures static flexibility in the lower back and hamstrings.

Static flexibility is often confused with joint laxity, which is a function of the joint capsule and ligaments. Ligamentous laxity has been associated with both increased and decreased risks of injury (Krivickas & Feinberg, 1996). Dynamic flexibility refers to the joint's ease of movement through its range of motion. Measurements are made by quantifying joint angle as force is generated or by using the damped oscillation technique (Gleim & McHugh, 1997). Dynamic flexibility would determine your ability to swing a golf club or tennis racket.

Static flexibility is easier to measure and, therefore, most research has been conducted using static flexibility as a measurement. Stretching can increase static flexibility. Recommendations by the American College of Sports Medicine (2000) for achieving and maintaining flexibility include using static or proprioceptive neuromuscular facilitation (PNF) stretching. The recommended frequency is two to three days per week to a position of mild discomfort, holding for 10 to 30 seconds with a static stretch, and a six-second contraction followed by a 10- to 30-second assisted stretch for PNF stretching. Stretches should be repeated three to four times for each major muscle group.

Research studies have examined the use of stretching to increase flexibility in sport injury and performance. In addition, the relationship between an individual's degree of flexibility and risk of injury or sport performance has also been investigated. Flexibility is specific to a given joint, side, and speed and, within sports, frequency or uniqueness of joint movements may influence range of motion. Therefore, being able to reliably predict a relationship between flexibility and injury or flexibility and performance is a challenging task.

Flexibility and Sports Injury 

Lack of flexibility as the cause of strains, sprains, and overuse injuries in sports is a widely held belief. Therefore, the inclusion of stretching exercises to increase flexibility to potentially reduce the frequency and severity of sports injuries is a common practice in many sport and athletic programs. Data to support these hypotheses are based largely on retrospective studies. Few prospective randomized control trials have been conducted. Results have been inconsistent and have limitations.

Inconsistent results can be found in the military population. Hartig and Henderson (1999) examined the inclusion of three hamstring stretching sessions to a basic training program in 298 military trainees over a 13-week period. An increase in hamstring flexibility was associated with a decrease in the number of lower-extremity injures. In contrast, Pope, Herbert, Kirwan, and Graham (2000) examined the inclusion of stretching for six major leg muscles during warm-up sessions with 1,538 male Army recruits over a 12-week period. The pre-exercise stretching did not result in a decrease in lower-extremity injuries. Jones and Knapik (1999) reviewed data regarding injury-control programs in the military population and found that both high and low levels of flexibility were identified as risk factors for training-related injuries.

Numerous limitations have been identified in other prospective studies. Van Mechelen, Hlobil, Kemper, Voorn, and deJongh (1993) examined the inclusion of standardized warm-up and stretching exercises in 421 recreational male runners. The intervention was not effective in reducing the number of running injuries. Limitations in this study included the reporting of noncompliance to the protocol, and it may be possible that jogging does not impose an excessive muscle length. Thus, increasing flexibility may not influence injuries. Bixler and Jones (1992) examined the role that half time stretching had on third-quarter injuries among five high school football teams. The intervention teams did show a decrease in injuries. Limitations in this study included the randomization process and co-interventions, thus preventing conclusive evidence suggesting stretching decreased injuries. Twellaar, Verstappen, Huson, and van Mechelen (1997) evaluated risk factors over a four-year period in physical education students. Results suggest that flexibility did not influence the number of injuries. The authors suggested it was difficult to find significant relationships due to the low number and great variety of sports injuries.

Gleim and McHugh (1997) reviewed approximately 18 studies of flexibility, stretching, and injury. Studies included a variety of populations such as football players, track and field athletes, gymnasts, soccer players, runners, ballerinas, rugby players, dancers, and Army trainees. Subjects were professional, college, master, and child athletes and included both males and females. No consistent findings were reported across the different populations or levels of competition and, therefore, the authors could not draw any conclusions about the effect of flexibility or stretching on injuries. The majority of studies were retrospective and thus did not address the issue of frequency of exposure and its relationship to injury rates.

Similarly, Shrier (1999) reviewed studies that included stretching before exercise and the effect on injury. Inconsistent findings were reported among the studies. Stretching appeared to be beneficial only if a warm-up was included. Several studies in running populations found that there was no difference in injury rate between stretchers and non-stretchers. Stretching was found to increase the risk of injury in several studies; however, the authors caution the interpretation of these studies due to the limitations.

In summary, the clinical data reviewed do not clearly suggest that flexibility or stretching decreases injuries. This is true for a variety of populations across gender and competition level. In fact, results of prospective studies indicate that stretching may actually increase injuries, particularly if it is done before exercise. Of those studies suggesting that stretching may be beneficial, a warm-up was also included as a co-intervention. There is a lack of data regarding the relationship of non pre-exercising stretching and injuries.

Flexibility and Sports Performance

The influence of flexibility on sport and athletic performance is most likely sport and position dependent. For example, a high degree of flexibility is necessary to be successful in gymnastics and swimming; whereas, different degrees of flexibility are seen among positions in football and baseball. Flexibility patterns and profiles observed across sports may be inherent or the result of training effects (Gleim & McHugh, 1997). Therefore, the relationship between flexibility and sports performance may be difficult to ascertain.

Hume, Hopkins, Robinson, Robinson, and Hollings (1993) examined psychological, physiological, and anthropometric correlates of gymnastics performance in 106 female gymnasts and found that flexibility was positively related to successful performance in rhythmic gymnastics. In contrast, Meckel, Atterbom, Grodjinovsky, BenSira, and Rotstein (1995) found that flexibility did not distinguish among 30 female 100-meter sprinters of different performance levels.

In addition to sport performance per se, measurements such as speed, strength, and economy have been examined to assess the relationship between flexibility and performance (Gleim & McHugh, 1997). For example, Cohen, Mont, Campbell, Vogelstien, and Loewy (1994) found that increased flexibility in the wrist and dominant shoulder were directly related to tennis-serve velocity in 40 tournament-level players. Brown, Niehues, Harrah, Yavorsky, and Hirshman (1988) examined relationships among range of motion and shoulder strength in professional baseball players. Pitchers and position players demonstrated different range-of-motion profiles and generated more torque at all isokinetic test speeds compared to position players. Furthermore, greater torques were produced for the dominant arm compared with the non-dominant arm at all test speeds.

The association between flexibility and strength has also been investigated, with inconsistent findings. Worrell, Smith, and Winegardner (1994) found that increased hamstring flexibility was associated with increased isokinetic torque production. Wilson, Elliott, and Wood (1992) found that bench-press performance was enhanced after eight weeks of flexibility training. Handel, Horstmann, Disckhuth, and Gulch (1997) found improvements in flexibility and torque production of the knee after an eight-week contact-relax stretch training program. In contrast, Kokkonen, Nelson, and Cornwell (1998) found that acute muscle stretching inhibited maximal strength performance. Rosenbaum and Hennig (1995) also demonstrated a short-term loss of strength after vigorous stretching.

The relationship between flexibility and running economy has also been examined. Running economy is defined as the submaximal steady-state aerobic demand (oxygen consumption, VO2) at a given running velocity (Conley & Krahenbuhl, 1980). A person with a lower submaximal VO2 at a given running velocity is considered more economical than a runner with a higher VO2. Factors accounting for differences in running economy include age, body temperature, fatigue, training, psychological mood states, gender, and biomechanical factors (Martin & Morgan, 1992; Morgan & Craib, 1992.) Flexibility is considered a biomechanical factor that has yielded inconsistent results among studies of running economy.

An early study by Godges, Macrae, Longdon, and Tinberg (1989) found improved economy in seven moderately athletic male college students when hip flexion and hip extension flexibility increased. Their results are consistent with the general belief that improved flexibility is desirable for optimal running performance. In contrast, Gleim, Stachenfeld, and Nicholas (1990) examined trunk and lower-limb flexibility in 100 male and female subjects aged 20 to 62, and found inflexibility was associated with a greater economy of walking and running. Craib, Mitchell, Fields, Cooper, Hopewell, and Morgan (1996) found that inflexibility in the trunk and lower limbs was associated with greater economy in 19 sub-elite male distance runners. Preliminary results from a current study by the authors also suggest that less trunk flexibility is associated with an increase in running economy of 10 female collegiate track athletes. It is suggested by the above studies that unproductive musculoskeletal movements are minimized in inflexible individuals, therefore reducing metabolic cost for the activity, and enhancing economy.

In summary, the studies reviewed show inconsistent results between flexibility and performance. Although increased flexibility may be important for performance in some sports and activities, decreased flexibility may also improve economy and performance in other activities.

In conclusion, the belief that increased flexibility is associated with a decrease in sports injury is not based on scientific evidence. Clinical evidence yields conflicting results and is subject to numerous limitations. The majority of studies examine the relationship of pre-exercise stretching and subsequent injury. Trends in these studies indicate an increase in injuries. However, warm-up in conjunction with pre-exercise stretching may reduce the risk of injuries, perhaps by counteracting the detrimental effects of stretching. Relative to performance and flexibility, generalizations cannot be made due to variation across sports, within sports, and variability in performance measures.

References

American College of Sports Medicine. 2000. ACSM's Guidelines for Exercise Testing and Prescription (6th ed). Philadelphia, PA: Lippincott, Williams & Wilkins.

Bixler, B., & Jones, R.L. 1992. High-school football injuries: effects of a post-halftime warm-up and stretching routine. Family Practice Research Journal, 12, 131-139.

Cohen, D.B., Mont, M.A., Campbell, KR., Vogelstein, BN., & Loewy, JW. 1994. Upper extremity physical factors affecting tennis serve velocity. American Journal of Sports Medicine, 22(6), 746-750.

Conley, D., & Krahenbuhl, G. 1980. Running economy and distance performance in highly trained athletes. Medicine and Science in Sports and Exercise, 12, 357-360.

Craib, M.W., Mitchell, V.A., Fields, K.B., Cooper, T.R., Hopewell, R., & Morgan, D.W. 1996. The association between flexibility and running economy in sub-elite male distance runners. Medicine and Science in Sports and Exercise, 28(6), 737-743.

Gleim, G.W., Stachenfeld, N.S., & Nicholas, J.A. 1990. The influence of flexibility on the economy of walking and jogging. Journal of Orthopaedic Research, 8, 814-823.

Gleim, G.W., & McHugh, M.P. 1997. Flexibility and its effects on sports injury and performance. Sports Medicine, 24(4), 289-299.

Godges, J.J., Macrae, H., Longdon, C., & Tinberg, C. 1989. The effects of two stretching procedures on hip range of motion and gait economy. Journal of Orthopedic Sports Physical Therapy, 7, 350-357.

Brown, L.P., Niehues, S.L., Harrah, A., Yavorsky, P., & Hirshman, H.P. 1988. Upper extremity range of motion and isokinetic strength of the internal and external shoulder rotators in major league baseball players. American Journal of Sports Medicine, 16(6), 577-585.

Handel, M., Horstman, T., Dickhuth, H.H., & Gulch, R.W. 1997. Effects of contract-relax stretching training on muscle performance in athletes. European Journal of Applied Physiology, 76(5), 400-4008.

Hartig, D.E., & 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.

Hume, P.A., Hopkins, W.G., Robinson, D.M., Robinson, S.M., & Hollings, S.C. 1993. Predictors of attainment in rhythmic sportive gymnastics. Journal of Sports Medicine and Physical Fitness, 33(4), 367-377.

Jones, B.H. & Knapik J.J. 1999. Physical training and exercise-related injuries. Surveillance, research and injury prevention in military populations. Sports Medicine, 27(2), 111-125.

Kokkonen, J., Nelson, A.G., & Cornwell, A. 1998. Acute muscle stretching inhibits maximal strength performance. Research Quarterly Exercise and Sport, 69(4), 411-415.

Krivickas, L.S., & Feinberg, J.H. 1996. Lower extremity injuries in college athletes: Relation between ligamentous laxity and lower extremity muscle tightness. Archives of Physical Medical Rehabilitation, 77, 1139-1143.

Martin, P.E., & Morgan, D.W. 1992. Biomechanical considerations for economical walking and running. Medicine and Science in Sports and Exercise, 24, 462-466.

Meckel, Y., Atterbom, H., Grodjinovsky, A., Ben-Sira, D., & Rotstein, A. 1995. Physiological characteristics of female 100 meter sprinters of different performance levels. Journal of Sports Medicine and Physical Fitness, 35(3), 169-175.

Morgan, D., & Craib, M. 1992. Physiological aspects of running economy. Medicine and Science in Sports and Exercise, 24, 456-461.

Pope, R.P., Herbert, R.D., Kirwan, J.D., & Graham, B.J. 2000. A randomized trial of preexercise stretching for prevention of lower-limb injury. Medicine and Science in Sports and Exercise, 32(2), 271-277.

Rosenbaum & Hennig. 1995. The influence of stretching and warm-up exercise on Achilles tendon reflex activity. Journal of Sports Science, 13, 461-490.

Shrier, I. 1999. Stretching before exercise does not reduce the risk of local muscle injury: a critical review of the clinical and basic science literature. Clinical Journal of Sports Medicine, 9, 221-227.

Twellaar, M., Verstappen, ET., Huson A., & van Mechelen, W. 1997. Physical characteristics as risk factors for sports injuries: a four year prospective study. International Journal of Sports Medicine, 18(1), 66-71.

Van Mechelen, W., Hlobil, H., Kemper, H.C., Voorn, W.J., & Jongh, H.R. 1993. Prevention of running injuries by warm-up, cool-down, and stretching exercises. American Journal of Sports Medicine, 21(5), 711-719.

Wilson, G.J., Elliot, B.C., & Wood, G.A. 1992. Stretch shorten cycle performance enhancement through flexibility training. Medicine and Science in Sport and Exercise, 24(1), 116-123.

Worrell, T.W., Smith, T.L., & Winegardner, J. 1994. Effect of hamstring stretching on hamstring muscle performance. Journal of Orthopedic Sports Physical Therapy, 20(3), 154-159.

Janet Whatley Blum and Christina M. Beaudoin are assistant professors of sports medicine at the University of South Maine.

Research Update is edited by Dr. Irma O'Dell of Southern Illinois University at Carbondale and Kim L. Siegenthaler, Ph.D. of Appalachian State University.