The Warm-up Procedure: To Stretch or-~ot to Stretch. A Brief Review

Transcription

1 L I T E R A T U R E R E V I E W The Warm-up Procedure: To Stretch or-~ot to Stretch. A Brief Review Craig A. Smith, BScl A n unwritten law of exercise among elite athletes and social exercisers is that warm-up prior to exercising is essential Sol- any program to be successful. Stretching is widely regarded as an important preexercise warm-up and a necessity for fitness, flexibility, and injury prevention. Warm-up exercises should be specific to the sport involved. They should promote flexibility and suppleness; exert sufficient effort on the musculoskeletal system to raise the body temperature; and warm or prime the muscles, tendons, and connective tissues. The warm-up should also stimulate the circulatory system, enhance coordination, and promote freer and easier movement due to a more compliant locomotor system. Inadequate warm-up exercises have been shown to be associated with strains to muscles and tendons (20). Muscle tightness is also thought to predispose athletes to certain injuries (13). It is generally accepted that warming up prior to exercise can reduce this incidence of injury (12,18,22). In vitro work by Safran et al (38) showed that warming up muscles with isometric exercise prior to stretch testing resulted in the conditioned muscles enduring more force until failure. They could be stretched to a greater limit before failing, and they showed relative increases in elasticity when compared with their contralateral muscles, which were not preconditioned with a warm-up. Further research has shown that even passively warming Stretching exercises are either performed alone or with other exercises as part of the athlete's warm-up. The warm-up is designed to increased muscle/tendon suppleness, stimulate blood flow to the periphery, increase body temperature, and enhance free, coordinated movement. The purpose of this paper is to review the literature regarding stretching, with the aim of defining its role during the warm-up. implications of stretching on muscle/tendon flexibility, minimizing injury, enhancing athletic performance, and generally preparing the athlete for exercise are discussed. Physiology applied to stretching is also discussed together with different related techniques and practical aspects. A proposed model stretching regime is presented based on the literature reviewed. Key Words: warm-up, stretching, flexibility ' Physiotherapist, private practice, 12A Chamberlain Street, Woodstock, Cape Town, South Africa 7925; Physiotherapist, South African National Cricket Team. At the time of this study, Mr. Smith was a senior clinical physiotherapist at UCT Sports Injuries Clinic, University of Cape Town, Cape Town, South Africa. the muscles increases the extensibility of the muscle/tendon unit (42) and affects joint flexibility (47). This may also help reduce athletic injury susceptibilitv. Beaulieu (2) suggests that a mild warm-up period should precede the stretching exercises. He adds that warmer muscles are more extensible, leading to less injury when stretched as well as increased gains in flexibility. This rationale has further supporting evidence (45,46). Work bv Henricson et al (2 I), although demonstrating that heat alone did not cause an increase in hip range of motion (ROM), showed that stretching resulted in two movements being increased, while heat and stretching combined resulted in the greatest increase in flexibility. Recordings of external rotation after stretching and flexion and abduction after heat and stretching were still increased after 30 minutes. Various studies have been undertaken to determine which exercises are best indicated for the warmup procedure. A study by Williford et al (50) showed that flexibility improved in a group of athletes who warmed up onlv with jogging followed by stretching and a group who warmed up only with stretching when testing shoulder, trunk, hamstring, and ankle flexibilitv. The results showed that the jogging followed by stretching group had significantly greater gains in ankle ROM than the stretching onlv group, while the stretching only group demonstrated better flexibility in the trunk region. The results did not show that warming up the muscles prior to stretching bv jogging was a superior method of warm-up, yet the authors concluded that both methods were effective in improving flexibilitv, with gains varied according to the body area. Hubley et al (23) compared the effects of 15 minutes of static stretching exercises and cycling on hip ROM (flexion and extension) and showed that both forms of exercise resulted in gains in ROM with no significant difference between the two exercises. Second measurements \'olume 19 Number I January 1994 JOSPT

2 after a further 15 minutes of either cycling or rest did not show significant differences from the initial gains of stretching. From their results, they concluded that both stretching and cycling were equally effective in increasing hip ROM and retaining this increase 15 minutes after the exercises. However, in a study to determine an effective method of improving ROM or flexibility (48). results showed that stretching, which consisted of an isometric contraction followed by relaxation and then passive extension (stretch) of the muscle, was superior to 15 minutes of warm-up cycling or 6-15 minutes of massage in increasing hip, knee, and ankle ROM. Furthermore, combining massage and warm-up did not show an improvement in ROM. The authors surmised that stretching was the best method of improving flexibility. STRETCHING BENEFITS The literature reports that stretching exercises benefit the athlete in several ways. First, stretching improves athletic flexibility (2,6,7,33, 39,48,50) by increasing muscle/tendon unit length transiently and the surrounding connective tissue length permanently (24). Perhaps the most well-known reason for stretching is injury prevention (2,5,6,12,14, 18,22,33,39), with some studies reporting decreased incidence of musculoskeletal injuries when their subjects embarked on a program of stretching exercises during their competitive season (14,29, 30,33). Flexibility imbalances (25) or reduced flexibility may be associated with certain injuries (1 2), and an adequate amount of flexibility gained from stretching may be helpful in the quest for superior athletic performance. Stretching may also influence running economy (1 7,19,45), enhance athletic performance (1,7,1 1,33), and improve joint ROM and athletic function during the rehabilitative phase of injury treatment (29.35). Finally, stretching is recommended as a method to alleviate muscle soreness following strenuous or prolonged activity (8.33) and has even been postulated as a way to enhance one's well-being (2). Ekstrand et al (1 4) studied a group of soccer players and showed that a test group that performed a 20-minute warm-up period, including 10 minutes of stretching exercises, had only 75% of the injuries of the control group of players. Stretching can also be part of the rehabilitative treatment program to prevent injury recurrence. Millar (29) found only a 1 % injury recurrence rate in patients who injured their calf muscles and were rehabilitated with a program comprising pain relief modalities, strengthening exercises, and a stretching routine Heat and stretching combined resulted in the greatest increase in flexibility. designed to return extensibility to the injured muscles. One of the consequences of limited flexibility is diminished efficiency of exercise (45). Could an athlete perform better when flexible or in a state of suppleness? A study by Godges et al (1 9) showed comparable results when evaluating two hip stretching techniques (static stretching and soft tissue mobilization with proprioceptive neuromuscular facilitation) on gait economy. The results suggested that both techniques effectively improved gait economy at 60% of V02 max. However, static stretching was more effective because it also demonstrated improvements at 40 and 80% of VO2 max. The authors ascribed the improvement in gait economy to increased hip ROM and suggested that stretching improved gait economy by applying the stretch to the muscles in the same plane in which they were going to be used. This philosophy seems to be in agreement with Cureton (7), who observed at the 1932 Olympic games that more flexible athletes were better performers. However, a study by De Vries (9) showed that acute increases in flexibility with stretching had little or no effect on the economy of exercise or energy expenditure for running a 100-m sprint. The results from the work of Gleim et al (1 7) contrast this effect even more. They studied the influence of stretching and gross flexibility on exercise economy and found that tighter subjects were significantly more economical fast walkers and joggers than looser, flexible subjects as tighter subjects demonstrated better oxygen consumption for treadmill walking and jogging. Furthermore, DeVries showed that individuals who possessed tightness in the trunk and lower extremities were more efficient at every treadmill speed tested. Therefore, there appear to be contradicting views in the literature concerning the influences of stretching and improved flexibility on the economy of exercise. The fact that only a few papers have been published on this topic implies that one cannot simply assume stretching will improve the economy of exercise; rather, it appears more work is needed to clarify this area before such statements or concepts can be accepted. Stretching has also been shown to effectively alleviate symptoms associated with delayed onset muscle soreness (DOMS) (36). In this study, DOMS was treated with a combination of heat or cryotherapy and stretching. Results showed that the combination of cryotherapy and static stretching was superior to that of cryotherapy and proprioceptive neuromuscular facilitation (PNF) stretching, or heat and static or PNF stretching. In another study where JOSPT \'olume 19 Number I ~Januav 1994

3 cryotherapy alone was used to treat DOMS, the results suggested that it was futile in alleviating the associated symptoms (5 1). Thus, the authors proposed that stretching might have been necessary to alleviate the muscle soreness. While many advocate stretching as a means of preexercise warm-up, some authors and athletes believe that stretching can do more harm than good, even leading to injury ( ). Knapic et al (25) found that female athletes whose hip extensors had a 15% greater ROM on the right side were 2.6 times more likely to be injured than those with less than a 15% imbalance. Subjects with greater ROM on the left side were only 1.7 times more likely to be injured. From these results, Knapic et al inferred that flexibility imbalances on either side of the body may predispose the athlete to injury. The interesting point is that the flexible sides were most likely to be injured. Although this may be true in part, one cannot emphatically declare that stretching is the direct cause of injury. Rather, it may be an erroneous technique (2) or overstretching into pain that causes microscopic muscle fiber tears, resulting in injury (1). APPLIED PHYSIOLOGY OF STRETCHING The musculoskeletal system has an inherent, built-in protective device made up of the muscle spindle and Golgi tendon organ, which are highly sensitive receptors acting to prevent overstretch of the passive joint structures and muscle/tendon unit, respectively. The muscle spindle is attached to intrafusal and extrafusal muscle fibers and is sensitive to active or passive stretch of the muscle. These receptors detect the degree of stretch applied to the muscle and control its dynamic length via the stretch reflex. The stretch receptors located in the tendons (Golgi tendon organs) are sensitive to tension and prevent overstretching in the opposite way to the stretch reflex. An increase in tension from either a large muscle contraction or overstretching activates the Golgi tendon organ receptors which, via the inverse stretch reflex, inhibit muscle contraction and induce relaxation. Thus, these receptors prevent the muscle from contracting in a way that damages itself. Recent evidence suggests that muscles and tendons also act viscoelastically in response to stretch (43). Elasticity implies that the change in muscle length is directly proportional to the applied load. Viscous properties are time- or rate-change dependent, where the rate of defor- There appear to be contradicting views in the literature concerning the influences of stretching and improved flextblli?, on the economy of exercise. mation is directly proportional to the applied force. The authors propose that flexibility of the muscle/tendon unit due to stretching occurs as a result of the viscoelastic nature of muscles. Therefore, stretching a muscle or group of muscles seems to induce muscle relaxation via either the inverse stretch reflex or the inherent viscoelastic property of the muscle (43), reducing tension in the muscle/ tendon unit and enabling the muscle to be stretched further (39.44). Immediate lengthening gained from stretching is mostly temporary and can be accredited to transitory sarcomeric lengthening (actin/myosin complex relaxation) (1 6). STRETCHING TECHNIQUES The three stretching techniques described in the literature are ballistic, static, and PNF. Proprioceptive neuromuscular facilitation normally requires assistance by a therapist and can thus be considered a combination active/passive stretch. Each procedure describes a type of stretch that can be applied to the muscle/ tendon unit, some more effectively and safely than others. Ballistic stretching involves repetitive bouncing movements in the muscle's lengthened position. It is considered less desirable and beneficial since more tension is created in the muscle (2,5) and the risk of injury is increased (32.33). Static stretching implies a slow stretch to the muscle held for 6-60 seconds (2,35.37). With the slow build-up in tension, the inverse stretch reflex is invoked, which induces relaxation in the muscle and enables further stretching (2,32,33) and increased flexibility (2). This method has the least associated injury risk and is believed to be the safest and most effective method of stretching (2.8.32). Proprioceptive neuromuscular facilitation, described by Knott and Voss (26), is a technique that when used to stretch a muscle applies the concepts of reflex activation and inhibition, ie., maximum contraction of the muscle leads to maximum relaxation of the same muscle. By this token of thinking, the muscle is first taken to its lengthened position and actively contracted against resistance such that when it relaxes through self-inhibition, it is stretched into the new available range. This procedure, referred to as contract relax, is commonly used when treating stiff and shortened tissues and is repeated a number of times, each time increasing the range of movement by Volume 19 Number 1 January 1994 JOSPT

4 stretching the muscle into its new lengthened range. Reciprocal relaxation, another technique also referred to in the PNF group, differs only slightly from contract relax. Contraction of the agonist muscle (for example, the quadriceps group) at the antagonist's end of range (hamstrings group) leads to reciprocal inhibition and relaxation of the antagonist muscle and the potential to stretch further. In his review of the literature on muscle stretching, Wilkinson (49) concluded that "the most effective stretching protocol for normal muscle was that of reciprocal relaxation." DeVries (lo) advocates static stretching as a superior technique to the ballistic method because there is less danger of exceeding tissue extensibility, the energy requirement is lower, and ballistic stretching often causes muscle soreness whereas static stretching is known to provide relief from muscle soreness. Sady et al (37) compared the effectiveness of ballistic, static, and PNF stretching on flexibility. They showed that PNF stretching was the only technique to cause significant increases in flexibility. However, these results were not demonstrated in a study comparing static stretching with soft tissue mobilization combined with PNF stretching for improving hip range of motion (1 9). The authors found both techniques of stretching to be equally effective. Starring et al (4 1) showed that cyclic stretching resulted in a greater gain in hip flexion ROM compared with static stretching of the hamstring muscles, although this finding was not statistically significant. Moore and Hutton (3 1) used electromyography in their study of static and PNF stretching techniques. They concluded that the PNF technique was the preferred method among subjects for achieving maximum gain in flexibility when subjects were experienced, motivated, and had sufficient time to practice, while the static technique seemed more desirable when comfort and limited training were the major factors. PRACTICAL ASPECTS OF STRETCHING: DURATION AND FREQUENCY From the literature, it is quite clear that stretching is regarded as an important component of any training routine of athletes, artists. or social exercisers. It is also evident that stretching plays an important part in improving flexibility, reducing the incidence of injury, and enhancing athletic performance. The mechanical strain imposed by stretching a contracted muscle is smaller in muscle with more slow-fwitch fibers than in muscle with more fast-twitch fibers. Therefore, the following question now needs to be addressed: what magnitude and duration of stretching is necessary in order to exert these beneficial effects? Tendons lengthen in proportion to the magnitude of the load applied to them (46), demonstrating best results with small loads over long periods as opposed to large loads over shorter periods (47). This model is true in theory but difficult in practical application. How does an athlete quantify a small load when performing a stretching routine? Furthermore, how long is a long period? How far does a muscle need to be stretched before it reaches its optimum stretched position? In a study by Taylor et al(43) on animal tendons, evidence suggests that the amount of stress relaxation occurring after the first seconds of stretching appears to be much less than the changes during the initial seconds of stretching. This would lead one to believe that there is a period during which the muscle/tendon unit maximally lengthens; stretching for a longer period will not result in significant increases in length. In a study by Bohannon (4) where subjects' hamstrings were maximally loaded for 8 minutes on 3 consecutive days in an attempt to improve straight-leg-raising (SLR) flexibility, results showed an insignificant 4.4" overall increase in SLR. Mean interim recordings after 15 seconds of loading on each day were greater than the day before, implying that the subjects maintained their flexibility from the previous day's stretching. Mean daily recordings after 8 minutes of loading and 10 minutes of rest were 3.7 and 2.6". Although these results suggest that muscle length was not overall sufficiently increased after 3 days, they do show the transient effect of short-term stretching. Further studies are needed to show whether stretching on a long-term basis will improve flexibility and how frequently and for how many days one needs to stretch to see results. Madding et al (28) compared three durations of a passive stretch (1 5 seconds, 45 seconds, and 2 minutes) on the ROM of hip abduction. They showed that hip abduction significantly increased and the resistance to abduction force significantly decreased for all three stretch groups. There were no significant differences of mean abduction between all three groups, except for the comparison of the 15- and 45- second groups. They attributed this difference to the small number of subjects in each group and from their study concluded that stretching for 15 seconds was just as effective as JOSPT Volume 19 Number I January 1994

5 stretching for 45 seconds or for 2 minutes. Wilkinson's (49) review on muscle stretching agrees with this viewpoint and also proposes that the stretch be held for approximately 15 seconds. The ideal number of stretches to perform during the routine is also debatable. Taylor et al (43). using rabbit extensor digitorurn longus and tibialis anterior muscle/tendon units, found that the greatest change in muscle/tendon length occurred in the first four stretches. Further stretching did not result in significant increases in length. Based on their study to determine the most effective method of improving joint flexibility, Wiktorsson-Moller et al (48) suggested that five to six repetitions are sufficient to increase hip, knee, and ankle ROM. The mechanical strain imposed by stretching a contracted muscle is smaller in muscle with more slowtwitch fibers than in muscle with more fast-twitch fibers (40). This implies that the elasticity of slow-twitch predominant muscle is greater than that of fast-twitch predominant muscle. Muscles that are composed of predominantly fast-twitch fibers are thought to be more susceptible to injury in humans (16). Thus, athletes who participate in high-intensity activities (such as sprinting and weight lifting) that utilize mainly fast-twitch fibers (32) might be required to stretch more frequently than endurance runners who utilize a greater proportion of slow-twitch fibers, as this type of muscle fiber has greater elastic properties and, thus, responds more favorably to stretching. PROPOSED STRETCHING ROUTINE In accordance with the majority of the authors, the following nine guidelines are proposed for stretching before or after exercise or at any time: I ) Develop a stretching program suitable to the needs of the sport (24). 2) The stretching program should be included as part of the warm-up and done at least minutes before exercising and again thereafter (2,14,24). Warm-up exercises before stretching also help to increase tissue extensibility (2,50). 3) Apply a slow static stretch (2,lO) and avoid bouncing (2.5) movements at the end of range to reduce the risk of injury (32,33). 4) Do not overstretch into pain but, rather, feel a stretch in the muscles (24) within one's level of tolerance (27). 5) Hold the stretch for seconds (2,4,43). 6) Each muscle group should be stretched three to five times for maximal benefit (43). 7) Stretch throughout the season and in the off-season to maintain flexibility. Improved flexibility can only be achieved through a longterm stretching program (4). 8) Always stretch agonists and antagonists and both limbs alternately (2). Avoid flexibility imbalance in muscle groups and limbs. 9) The art and activity of stretching should be enjoyed to derive maximum benefit so that it never becomes a burdensome task. SUMMARY Stretching to improve musculotendinous flexibility and joint suppleness is common during the warm-up routine of social exercisers and elite athletes. Its benefits and the rationale of stretching have been reviewed. Most authors agree that for each muscle group, three stretches each held for approximately 15 seconds will exert the best effect. Further clinical studies are needed to elucidate more information on this subject. JOSYI' REFERENCES 1. Anderson 6: Stretching, London: Pelham Books, 1988 Beaulieu le: Developing a stretching program. Phys Sportsmed 9:59-69, 1981 Benjamin 6, Roth P: Warm-up versus stretching. 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6 intercollegiate football players. Am I Sports Med 12(5): , Henricson AS, Fredriksson K, Persson I, Pereira R, Rostedt Y, Westlin NE: The effect of heat and stretching on range of hip motion. I Orthop Sports Phys Ther 6(2): , Hubley CL, Kozey lw: Can stretching prevent athletic injuries?/ Musculoskel Med 1 (9):25-32, Hubley CL, Kozey IW, Stanish WD: The effects of static stretching exercises and stationary cycling on range of motion + the hip joint. I Orthop Sports Phys Ther 6(2): , lacobson C, Speechley E: Soccer- Warming up and stretching. S Afr I Sports Med 5(3): 17-18, Knapic 11, Bauman CL, /ones BH, Harris lm, Vaughan L: Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes. Am I Sports Med 19:76-81, Knott M, Voss DE: Proprioceptive Neuromuscular Facilitation: Patterns and Techniques (2nd Ed), New York: Harper & Row, Kottke FI, Stillwell CK, Lehman IF: Therapeutic exercise to maintain mobility. In: Krussne's Handbook of Physical Medicine and Rehabilitation, pp Philadelphia: W.B. Saunders Company, Madding SW, Wong /C, Hallum A, Medeiros lm: Effects of duration ofpassive stretch on hip abduction range of motion. I Orthop Sports Phys Ther 8: , Millar AP: An early stretching routine of calf muscle strains. Med Sci Sports Exerc 8:39-42, Millar AP: Strains of the posterior calf musculature (tennis leg). Am I Sports Med 7: , Moore MA, Hutton RS: Electromyographic investigation of muscle stretching techniques. Med Sci Sports Exerc 12: , Noakes TD: Lore of Running, Cape Town, South Africa: Oxford University Press, Noakes TD, Granger 5: Running Injuries, Cape Town, South Africa: Oxford University Press, Osler 7: Serious Runners Handbook, Mountain View, CA: World Publications, Peterson L, Renstrom P: Sports Injuries. Their Prevention and Treatment, Cape Town, South Africa: luta, Prentice WE: An electromyographic analysis of the effectiveness of heat or cold and stretching for inducing relaxation in injured muscles. I Orthop Sports Phys Ther 3: , Sady SP, Wortman MA, Blanke D: Flexibility training. Ballistic, static or proprioceptive neuromuscular facilitation. Arch Phys Med Rehabil 63: , Safran MR, Carrett WE Ir, Seaber AV: The role of warm-up in muscular injury prevention. Am 1 Sports Med l6(2): , Schultz P: Flexibility: Day of the stretch. Phys Sportsmed 7: , Siff MC: Biomechanical issues in strength and flexibility conditioning. In: Proceedings of the Second South African Sports Medicine Association Congress, Cape Town, South Africa, April lohannesburg, South Africa: Medical News Tribune, Starring DT, Cossman MR, Nicholson CC Ir: Comparison of cyclic and sustained passive stretching using a me- chanical device to increase resting length of hamstring muscles. Phys Ther 68(3): , Strickler 7, Malone 7, Carrett WE: The effects of passive warming on muscle. Am I Sports Med 18: , Taylor DC, Dalton ID, Seaber AV, Carrett WE jr: Viscoelastic properties of muscle-tendon units: The biomechanical effects of stretching. Am I Sports Med 18: , Taylor DC, Seaber AV, Carrett WE jc Response of muscle tendon units to cyclic repetitive stretching. Trans Orthop Res Soc 1 O:84, Wadsworth IS, Smidt CL, lohnston RC: Gait characteristics ofsubjects with hip disease. Phys Ther 52: , Warren CG, Lehmann IF, KoblanskilN: Elongation of rat tail tendon: Effect of load and temperature. Arch Phys Med Rehabil5 l: , Warren CC, Lehmann IF, Koblanski IN: Heat and stretch procedures: An evaluation using rat tendon tail. Arch Phys Med Rehabil57: , Wiktorsson-Moller M, Oberg B, Ekstrand 1, Cillquist I: Effects of warming up, massage and stretching on range of motion and muscle strength in the lower extremity. Am / Sports Med 1 1: , Wilkinson A: Stretching the truth. A review on the literature on muscle stretching. Aust Physiother 38: , Williford HN, East IS, Smith FH: Evaluation of warm-up for improvement in flexibility. Am I Sports Med 14: , Yackzan L, Adams C, Francis KT: The effects of ice massage on delayed onset soreness. Am I Sports Med 12: , 1984 JOSPT Volume I9 Number I January 1994