An Update on FlexibilityRussell T. Nelson, PhD, PT, SCS, ATCOrthopedic Specialists,Texarkana,Texas

William D. Bandy, PhD, PT, SCS, ATCUniversity of Central Arkansas, Conway, Arkansas

© National Strength and Conditioning AssociationVolume 27, Number 1, pages 10–16

Keywords: flexibility; static stretching; dynamic range of motion

Most medical professionals,coaches, and athletes consideraerobic conditioning, strength

training, and flexibility to be integralcomponents in any conditioning pro-gram (7, 10, 19, 20, 25, 31). Some ofthe proposed benefits of enhanced flexi-bility are reduced risk of injury (7, 10,19, 20, 25, 31), pain relief (20), and im-proved athletic performance (3, 50). A

lack of definitive research makes it diffi-cult to make recommendations regard-ing an effective flexibility program.

The purpose of this article is to providean update on the latest research regard-ing flexibility training. Definitive re-search will assist in dispelling commonmisconceptions often associated withflexibility training.

Full range of motion across a joint is de-pendent on 2 components: joint rangeof motion and muscle length (52). Jointrange of motion is the motion availableat a single joint and is influenced bybony structures, ligaments, and the cap-sule. Muscle length and flexibility areused interchangeably to describe theability of a muscle to lengthen to allow 1joint (or more than 1 joint in a series) tomove through a range of motion(ROM). Loss of flexibility is defined as adecrease in the ability of a muscle to de-form (52).

Other authors have defined flexibility ina similar fashion. Anderson and Burke(3) defined flexibility as the range ofmotion of a joint or series of joints thatare influenced by muscles, tendons, liga-ments, bones, and bony structures. De-Vries (14) suggested that flexibility is

the measured range of motion availableabout a joint or series of joints.

Types of Stretching

Ballistic StretchingBallistic stretching is a technique involv-ing a rhythmic bouncing motion. Themuscle to be stretched is held stationarywhile the nonstationary lever is rhyth-mically bounced. The bouncing utilizesthe momentum of the extremity tolengthen the muscle (3). Significant in-creases in ROM have been documentedthrough the use of ballistic stretching,but many argue that the rigorous energyused in this technique places the subjectat an increased risk of muscle injury (20,25, 31, 46, 49). Also, the use of hightension over a short period of time doesnot correlate with the use of low forceover an extended period of time, whichhas been found to be most effective forstretching a muscle (43).

An argument can be made that manysporting activities involve high-tensionor intensity, short-duration eccentriccontractions and that to properly pre-pare an athlete for these events a degreeof limited ballistic activity is necessary.The sporting activity may place the ath-lete at a much higher risk than would a

s u m m a r y

Most medical professionals, coach-

es, and athletes consider flexibility

training an integral component of

any conditioning program. Defini-

tive research will assist in dis-

pelling common misconceptions

often associated with flexibility

training. The purpose of this article

is to provide an update on the lat-

est research regarding flexibility

training.

10 February 2005 • Strength and Conditioning Journal

controlled ballistic stretching program.A study by Vujnovich and Dawson (48)found that by following a static stretchwith a ballistic stretch, they were able tosignificantly decrease the activity ofmotor neurons within the L5–S1 spinalsegment. These reported results indicatethat static stretching alone provides thisinhibition as well, but not to the extentthat static stretching followed by a bal-listic stretch does. Eccles et al (16) sug-gested that the inhibition of the motorneuron during ballistic stretching butnot during static stretching is due to theGolgi tendon organ. The Golgi tendonorgan is insensitive to slow velocitylength changes of muscle in intactpreparations (11, 21, 22) but provides adynamic response during rapid stretch-ing (2, 17, 22, 26).

Contrary to the decrease in motor neu-ron activity reported by Vujnovich andDawson (48), Guissard et al (18) report-ed that ballistic stretching caused the fa-cilitation of the stretch reflex, which ismediated by the facilitatory influencesof muscle spindle type Ia and II recep-tors upon homonymous alpha motorneuron excitability. This activation ofthe stretch reflex causes a contraction inthe muscle being stretched. Therefore,as the individual bounces, the muscle re-sponds by contracting to protect itselffrom overstretching. Also, eliciting themyostatic stretch reflex increases themagnitude and rate of the stretch, whichcan, theoretically, strain or rupture themuscle. Irrespective of the influence onthe motor neurons reported in the liter-ature, the typical flexibility programdoes not incorporate ballistic stretching(52).

Proprioceptive NeuromuscularFacilitationProprioceptive neuromuscular facilita-tion (PNF) was introduced in 1968 byKnott and Voss (28), who defined themethod as a way of “promoting or has-tening the neuromuscular mechanismthrough stimulation of the propriocep-tors.” PNF has been used to increase

strength and flexibility and to enhancecoordination. Specific to increasing flex-ibility of muscle, PNF techniques in-volve the use of brief isometric contrac-tions of the muscle to be stretched priorto statically stretching the muscle. Thesetechniques facilitate the Golgi tendonorgan in the muscle performing the iso-metric contraction, causing autogenicinhibition in that muscle and allowingelongation. In the technique referred toas contract relax, the subject performsan isotonic contraction while anotherperson trained in PNF resists the mo-tion. The subject performing the con-traction is then instructed to relax. Theassistant then moves the extremity pas-sively through as much range as possi-ble, to the point where limitation isagain felt to occur.

Sady et al (41) compared the effects ofstretching techniques on the flexibilityof the trunk, shoulders, and hamstringsin 43 college-aged men. Baseline mea-sures were obtained, and then the sub-jects began a 6-week program using stat-ic stretching, ballistic stretching, orPNF. The measurements following the 6weeks of stretching revealed that thesubjects performing the PNF techniquehad the most improved range of motionin all 3 areas stretched.

A limitation with the use of PNF is thatPNF requires 1-on-1 intervention withan experienced individual (28, 39).Other stretching can easily be per-formed without any outside interven-tion.

Static StretchStatic stretching is elongating a muscleto tolerance and sustaining the positionfor a length of time (3, 30). According toSmith (45), static stretching has the leastassociated injury risk and is believed tobe the safest technique compared withother stretching techniques. Numerousauthors have stressed the importance ofstatic stretching as a part of training forathletics and sports medicine (1, 12, 29,37, 42, 44) and have indicated that stat-

ic stretching is the most commonmethod of stretching used to increasethe flexibility of the muscle (41, 52).Static stretching is the most commonlyused form of flexibility training becauseit carries the lowest risk of injury, doesnot require 1-on-1 intervention with anexperienced individual, and is effectivefor improving flexibility.

Bandy and Irion (6) performed a studyin which subjects stretched for 0, 15, 30,and 60 seconds 5 days a week for 6weeks. The study found that 30 and 60seconds of stretching were each more ef-fective at increasing flexibility thanstretching for 15 seconds or not stretch-ing at all. No significant difference oc-curred between those stretching for 30and 60 seconds, indicating that 30 sec-onds of stretching was as effective as 1minute.

Bandy et al (7) also examined the effectsof time and frequency of static stretch-ing on flexibility. A total of 93 subjectswere assigned to 1 of 5 groups. The 4stretching groups stretched 5 days aweek for 6 weeks. Group 1 performed 31-minute static stretches of the ham-string muscles with a 10-second rest inbetween. Group 2 performed 3 30-sec-ond static stretches with a 10-secondrest in between. Group 3 performed 1static stretch for 1 minute. Group 4 per-formed 1 static stretch for 30 seconds,and group 5 served as a control. The re-sults of this study suggest that 1 30-sec-ond duration static stretch is an effectivemethod of stretching the hamstringmuscle in order to increase range of mo-tion. No further increased range result-ed from either increased frequency orduration (7).

Dynamic Range of MotionDynamic range of motion (DROM) is arelatively new method used to lengthena muscle. The method is described byMurphy (34, 35) as a technique that al-lows the muscle being lengthened toelongate naturally and in its relaxedstate. This elongation is achieved by

11February 2005 • Strength and Conditioning Journal

contracting the antagonist muscle andmoving the joint the muscle crossesthrough the full available range in a slowand controlled manner. For example, ifthe subject was stretching the hamstringmuscles dynamically, he or she wouldcontract the quadriceps muscles and ex-tend the knee. The extension to the endrange of motion would cause the ham-string to elongate. The firing of the an-tagonistic muscle (in this example, thequadriceps) will cause the agonist ham-strings to relax through reciprocal inhi-bition (38).

Murphy (35) provided several argu-ments for using DROM instead of apassive type of stretching activity.First, DROM can increase the temper-ature within the working muscle (33).Studies have shown that a warmedmuscle produced faster and moreforceful contractions (33), improvedmuscular work (33,42), and increasedspeed of the transmission of the nerveimpulses (42). Second, Murphy (35)argued that dynamically stretching amuscle after exercise will increaseblood flow to the region, thus remov-ing lactic acid and possibly reducingdelayed onset muscle soreness (de-scribed later in the literature review).The properties of static stretching maynot afford this capability because ofthe passive nature of static stretching.Third, Murphy (35) went on to suggestthat while static stretching is the mostpopular technique for improving flexi-bility, it has not been proven to im-prove athletic performance.

Hubley et al (23) performed a study on30 subjects between 14 and 60 years ofage to compare the effects of 15 minutesof static stretching and 15 minutes ofstationary cycling on flexibility for bothhip flexion and extension. Measure-ments were taken following a full expla-nation of the experimental procedure,immediately after the static stretching orcycling, and 15 minutes later. The au-thors found no difference in gains in hipflexion and hip extension between the 2

groups measured immediately or 15minutes after the activity. The authorsconcluded that both stretching and cy-cling were found to be equally beneficialexercises for “increasing (immediate postmeasure) and maintaining (15 minutepost measure)” the increase in flexibility.

Conversely, Bandy et al (8) comparedDROM to static stretching to improveflexibility in the hamstrings. Fifty-eightsubjects participated in the study. Onegroup performed DROM 5 days a weekby lying supine with the hip held in 90degrees of flexion. The subject then ac-tively moved the leg into extension andheld the leg in the end range for 5 sec-onds, then slowly lowered the leg. Themovements were performed 6 times persession. The second group performed 130-second static stretch 5 days a week.The third group served as a control. Theauthors found that although both staticstretch and DROM increase hamstringflexibility, a 30-second static stretch wasmore effective than DROM for enhanc-ing flexibility. The gains made by thosewho statically stretched were more thandouble the gains made by those subjectswho stretched dynamically.

Eccentric Flexibility Training Recently, eccentric training through afull range of motion has been introducedin the literature as a method to increasehamstring flexibility (36). To performeccentric training through a full range ofmotion, each subject laid supine with theleg that was not being stretched straight.In each hand the subject held an end of a3-foot piece of black resistance band,with the leg to be stretched locked in fullextension and the hip in neutral. Thesubject was instructed to bring the hip tobe stretched into full hip flexion bypulling with both arms on the resistanceband attached to the foot, making surethe knee remained locked in full exten-sion at all times. Full hip flexion was de-fined as the position of hip flexion atwhich a gentle stretch was felt by thesubject. As the subject pulled the hipinto full flexion, the subject was instruct-

ed to simultaneously resist the hip flex-ion by eccentrically contracting the ham-string muscles. The extremity was thenbrought back into hip extension.

Nelson and Bandy (36) investigated theeffectiveness of eccentric trainingthrough the full range of motion bycomparing 3 types of stretching activi-ties in high school-aged males. The firstgroup performed a 30-second staticstretch 4 times a week over a 6-week pe-riod of time. The second group eccentri-cally trained the hamstring musclethrough a full range of motion 4 times aweek for 6 weeks. The third group per-formed no flexibility training and servedas the control group. At the end of thestudy, the control group had gained anaverage of 1.17° of motion over the 6-week period, while the static stretch andeccentric training groups gained 12.04°and 12.79° respectively. Posttest mea-sures indicated no significant differ-ences between the static stretch and ec-centric training groups, but there was asignificant difference between thegroups performing flexibility trainingand the control group. The authors feltthat if you combine the benefits of aneccentric training program (strengthgains, possible reduction of injury rates,and specificity of training) with range ofmotion gains equal to that of staticstretching, compelling evidence exists toincorporate eccentric training into anexercise program.

Proposed Benefits of Stretching As indicated in the previous section, avariety of types of stretching techniquesexist for increasing flexibility. The rea-son that so much time and energy hasbeen allotted to researching the appro-priate stretching technique is that it hasbeen suggested that an effective stretch-ing program can warm the muscles, de-crease pain, increase stretch tolerance,assist in returning the body to a moresteady state, reduce the risk of injury,and improve athletic performance (34).Previous research examining each ofthese claims will now be examined.

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Increase Temperature of the MuscleAs muscle temperature rises, the meta-bolic processes increase and viscositythroughout the muscle decreases (29). Anincrease in the metabolic rate and a de-crease in viscosity lead to a smoother con-traction of the muscle and an increase inoxygen uptake; changes which result inimproved muscle function. Research hasfound that higher muscle temperaturesalso speed up the transmission of nerveimpulses (42), which may produce fasterand more forceful contractions (33).Blood traveling through a warmed mus-cle also increases in temperature. Asblood temperature rises, oxygen morereadily dissociates from hemoglobin andthus is delivered to the tissues more effi-ciently. This change makes more oxygenavailable to working muscles (4).

Murphy (34) argued that a typical flexi-bility program consisting of only staticstretching does nothing to warm themuscles, and the heating benefit to themuscle is not achieved. If a muscle is sta-tically stretched, no warming effect oc-curs. A more appropriate procedure forwarming is through active contractions,which is why Murphy (34) suggestedthat active or dynamic range of motionactivities were better to utilize in prepar-ing a muscle for activity.

Effect on Injury RatesThe reason most often given for incor-porating a stretching program into anyathletic endeavor is to reduce thechances of injury. Although several au-thors suggest that stretching will reduceinjuries (7, 10, 19, 20, 25, 31), empiri-cal evidence is lacking. Levine et al (32)sampled stretching programs of inter-collegiate athletes to determine tenden-cies in stretching practices. The studyfound that the hamstrings were amongthe muscle groups stretched by mostathletes (92%). The study also statedthat hamstring strains were one of themost reported injuries. Cross and Wor-rell (13) incorporated a flexibility pro-gram for a football team and reported a

decrease in the number of lower extrem-ity injuries. However, no data was pro-vided indicating whether or not theplayers made gains in the amount offlexibility after incorporating this pro-gram. The authors concluded that theybelieved many factors were involved inthe reduction in the number of injuries.

Jonhagen et al (27) compared 11 sprint-ers with a history of a previous hamstringinjury with 9 uninjured runners. Mea-surements compared in each group wereflexibility, concentric torque, and eccen-tric torque of the quadriceps and ham-string muscles at different velocities. Theauthors found that the sprinters with ahistory of a previous injury had signifi-cantly tighter hamstrings than the unin-jured sprinters. The uninjured sprintershad significantly higher eccentric ham-string torques at all velocities and hadsignificantly higher torques concentri-cally in the quadriceps and hamstringswhen tested at 30º per second. The au-thors concluded that the sprinters with ahistory of hamstring injury differed fromtheir counterparts in that they wereweaker at all speeds eccentrically and atlow speeds concentrically, and they alsowere significantly less flexible.

Contrary to popular public opinion, sev-eral authors have found that stretchingdoes not reduce the risk of injury (1, 24,40, 43, 47, 49). Hubley-Kozey and Stan-ish (24) performed a literature reviewand, although the authors concluded thata stretching program should become anintegral part of an athlete’s trainingregime, they also stated that no proof ex-ists that stretching (static, ballistic, orPNF) can reduce the risk of injury. In areview of the literature, Agre (1) reportedthat the most commonly cited cause ofhamstring strains was weakness in thehamstring muscles. But, in the studiescited, the author did not find a signifi-cant relationship between hamstring flex-ibility and hamstring strain injuries. VanMechelen et al (47) found that, while ahealth education intervention was effec-tive in improving specific knowledge of

warm-up and cool-down techniques, theintervention was not effective in reducingthe number of running injuries.

Shrier (43) reviewed 5 studies and gaveseveral reasons as to why stretching be-fore exercise would not prevent injuries.First, stretching before exercise shouldhave no effect for activities in which ex-cessive muscle length is not an issue. Ac-tivities such as long distance runningand cycling do not require a great deal ofrange of motion. If the activity per-formed does not require a great deal ofhamstring flexibility, it is not necessaryto spend a great deal of time stretchingthe hamstrings. Second, stretching willnot affect muscle compliance during ec-centric activities, when most strains arebelieved to occur. If most injuries occurduring the eccentric phase of activity,the rate of injury would be more effec-tively reduced by being activity specificand performing eccentric activities.Third, stretching can produce damage atthe cytoskeleton level. According toShrier (43), the passive force placed onthe muscle causes microtrauma in themuscle being stretched. Continued mi-crotrauma to a muscle will weaken andpredispose the muscle to injury. Fourth,stretching appears to mask pain in hu-mans. The increase in stretch tolerancemay mask the pain that is necessary forthe muscle to react to prevent an injury.

A study by Worrell et al (49) examinedathletes participating in high-risk sport-ing activities and compared noninjuredathletes with athletes who had sustaineda hamstring injury in the past 18months. The athletes were tested isoki-netically, and the flexibility of each ath-lete was measured. Isokinetically thestrength values were similar for bothgroups. The researchers did find thatthose athletes with a history of a ham-string injury had a lack of flexibilitycompared with their uninjured counter-parts. The authors stated that the lack offlexibility following a hamstring injuryneeded to be at the top of the priority listas far as rehabilitation is concerned (49).

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The authors took this particular study astep further and included having eachathlete fill out a questionnaire. One ofthe most interesting findings in the ques-tionnaire was that 81% of the athleteswith hamstring injuries had performedsome type of hamstring stretching tech-nique before they were injured.

Pope et al (40) performed a study on theeffect of muscle stretching during warm-up on the risk of exercise related in-juries. The authors followed 1,538 maleArmy recruits and concluded that a typi-cal muscle-stretching protocol per-formed during pre-exercise warm upsdid not produce clinically meaningfulreductions in risk of exercise related in-jury in Army recruits.

Effect on Athletic PerformanceAnderson and Burke (3) stated that opti-mal flexibility aids in athletic perfor-mance, but they do not support thisclaim with any evidence. Dintiman (15)performed a study related to sprint train-ing by dividing athletes into 5 groups.The first group underwent sprint train-ing combined with a static stretchingprogram. A second group underwent aconventional sprint training programcombined with a weight-training pro-gram. A third group combined sprinttraining, a weight-training program, anda static-stretching program. The fourthgroup underwent sprint training only,and the fifth group was a control. Thetraining involved 145 subjects and lasted8 weeks. The results indicated that nodifference existed in improvement ofrunning speed between the group thatunderwent sprint training combinedwith static stretching and the group thatunderwent sprint training alone. Thegroups incorporating a weight-trainingprogram as well as a flexibility programwith the sprint training made significant-ly more improvements than the sprint-training program alone. The group sup-plementing the sprint training with aweight program did not improve signifi-cantly more than the group only per-forming sprint training.

The following studies have actuallyfound a decrease in athletic performanceas a result of static stretching. Avela et al(5) had 20 healthy male subjects partici-pate in a study in which they underwentrepeated passive stretching of the calfmuscles. The authors found a clear dete-rioration of the muscle function follow-ing the stretching program, as indicatedby a 23.2% decrease in torque. The au-thors suggested that these changes wereassociated with “a clear immediate re-duction in the reflex sensitivity,” result-ing from the reduced sensitivity of themuscle spindles to repeated stretch.

Behm et al (9) measured isometric maxi-mum voluntary contraction force of thequadriceps and hamstring muscles in 18subjects. Six subjects were placed in acontrol group, and 12 subjects in thestudy group had the same measurementstaken 5 to 10 minutes after a 20-minutebout of static stretching. The authorsfound that a significant decrement(12%) occurred in maximum voluntarycontraction force after stretching in the12 subjects performing the staticstretching. No significant changes werefound in the control group.

A study by Young and Behm (51) exam-ined the effects of submaximal running,static stretching of the quadriceps andgluteal muscles, and practice jumps onvertical jump height. The authors foundthat 4 minutes of submaximal runningand practice jumps provided significant-ly greater vertical jump height than stat-ic stretching. Young and Behm (51) con-cluded that “stretching produced anegative effect on performance and amore realistic athletic warm-up wouldbe beneficial”.

ConclusionA lack of definitive research makes fordifficulty in making recommendationsregarding effective flexibility programs.As indicated in this literature review, themost commonly used form of flexibilitytraining for increasing flexibility is staticstretching, but questions exist as to

whether static stretching can reduce in-jury rates and improve athletic perfor-mance. The search continues for an ac-tivity that will increase flexibility as wellas static stretching does. If an activity isfound that will accomplish this task,other avenues of research will be open todetermine if gains are made in strength,injury reduction, and performance im-provement.

Two activities of interest as an alterna-tive to the static stretch for increasingflexibility of a muscle are PNF and ec-centric training. One limitation of PNFtraining is the need for a trained personto assist with the activity. The assistanceneeded with PNF may cause that formof flexibility training to be used lessoften, even though the research proves itto be a very good alternative to staticstretching. As indicated in the literature,training a muscle eccentrically has beenreported to strengthen the muscle, aswell as provide neuromuscular adapta-tions which may also reduce the chancesof injury in the hamstring muscles.More research is needed to determinewhether the eccentric range of motionactivity can actually improve strengthwhile improving flexibility. ♦

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Winegardner. Effect of hamstringstretching on hamstring muscle per-formance. J. Orthop. Sports Phys. Ther.20:154–159. 1994.

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AAcckknnoowwlleeddggmmeenntt:: This feature was writ-ten in partial fulfillment of a PhD at theUniversity of Central Arkansas.

Russell Nelson is the director of physicaltherapy at Orthopedic Specialists ofTexarkana in Texarkana, Texas. He is teamtrainer for Arkansas High School andtraining consultant for Texarkana CollegeAthletics.

William Bandy is a Professor in the De-partment of Physical Therapy at the Uni-versity of Central Arkansas in Conway,Arkansas.

16 February 2005 • Strength and Conditioning Journal

Nelson

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